Clean up the bindings APIs (#86438)

dev/benchmarks/complex_layout/test_memory/scroll_perf.dart

@@ -32,7 +32,7 @@ Future<void> main() async {
       child: ComplexLayoutApp(),
     ),
   ));
-  await SchedulerBinding.instance?.endOfFrame;
+  await SchedulerBinding.instance.endOfFrame;
 
   /// Wait 50ms to allow the raster thread to actually put up the frame. (The
   /// endOfFrame future ends when we send the data to the engine, before
@@ -50,9 +50,9 @@ Future<void> main() async {
       child: ComplexLayoutApp(),
     ),
   ));
-  await SchedulerBinding.instance?.endOfFrame;
+  await SchedulerBinding.instance.endOfFrame;
 
-  final WidgetController controller = LiveWidgetController(WidgetsBinding.instance!);
+  final WidgetController controller = LiveWidgetController(WidgetsBinding.instance);
 
   // Scroll down
   for (int iteration = 0; iteration < maxIterations; iteration += 1) {

dev/benchmarks/macrobenchmarks/lib/src/filtered_child_animation.dart

@@ -41,7 +41,7 @@ class _FilteredChildAnimationPageState extends State<FilteredChildAnimationPage>
     _filterType = widget.initialFilterType;
     _complexChild = widget.initialComplexChild;
     _useRepaintBoundary = widget.initialUseRepaintBoundary;
-    WidgetsBinding.instance!.addPostFrameCallback((_) {
+    WidgetsBinding.instance.addPostFrameCallback((_) {
       final RenderBox childBox = _childKey.currentContext!.findRenderObject()! as RenderBox;
       _childCenter = childBox.paintBounds.center;
     });

dev/benchmarks/macrobenchmarks/lib/src/large_images.dart

@@ -11,7 +11,7 @@ class LargeImagesPage extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final ImageCache imageCache = PaintingBinding.instance!.imageCache!;
+    final ImageCache imageCache = PaintingBinding.instance.imageCache;
     imageCache.maximumSize = 30;
     imageCache.maximumSizeBytes = 50 << 20;
     return GridView.builder(

dev/benchmarks/macrobenchmarks/lib/src/web/bench_mouse_region_grid_hover.dart

@@ -66,7 +66,7 @@ class BenchMouseRegionGridHover extends WidgetRecorder {
   void frameDidDraw() {
     if (!started) {
       started = true;
-      SchedulerBinding.instance!.addPostFrameCallback((Duration timeStamp) async {
+      SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) async {
         _tester.start();
         registerDidStop(_tester.stop);
       });
@@ -124,7 +124,7 @@ class _UntilNextFrame {
   static Future<void> wait() {
     if (_UntilNextFrame._completer == null) {
       _UntilNextFrame._completer = Completer<void>();
-      SchedulerBinding.instance!.addPostFrameCallback((_) {
+      SchedulerBinding.instance.addPostFrameCallback((_) {
         _UntilNextFrame._completer!.complete(null);
         _UntilNextFrame._completer = null;
       });
@@ -145,7 +145,7 @@ class _Tester {
   TestGesture get gesture {
     return _gesture ??= TestGesture(
       dispatcher: (PointerEvent event) async {
-        RendererBinding.instance!.handlePointerEvent(event);
+        RendererBinding.instance.handlePointerEvent(event);
       },
       kind: PointerDeviceKind.mouse,
     );

dev/benchmarks/macrobenchmarks/lib/src/web/bench_mouse_region_grid_scroll.dart

@@ -41,7 +41,7 @@ class BenchMouseRegionGridScroll extends WidgetRecorder {
   void frameDidDraw() {
     if (!started) {
       started = true;
-      SchedulerBinding.instance!.addPostFrameCallback((Duration timeStamp) async {
+      SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) async {
         _tester.start();
         registerDidStop(_tester.stop);
       });
@@ -96,7 +96,7 @@ class _UntilNextFrame {
   static Future<void> wait() {
     if (_UntilNextFrame._completer == null) {
       _UntilNextFrame._completer = Completer<void>();
-      SchedulerBinding.instance!.addPostFrameCallback((_) {
+      SchedulerBinding.instance.addPostFrameCallback((_) {
         _UntilNextFrame._completer!.complete(null);
         _UntilNextFrame._completer = null;
       });
@@ -117,7 +117,7 @@ class _Tester {
   TestGesture get gesture {
     return _gesture ??= TestGesture(
       dispatcher: (PointerEvent event) async {
-        RendererBinding.instance!.handlePointerEvent(event);
+        RendererBinding.instance.handlePointerEvent(event);
       },
       kind: PointerDeviceKind.mouse,
     );

dev/benchmarks/macrobenchmarks/lib/src/web/bench_mouse_region_mixed_grid_hover.dart

@@ -85,7 +85,7 @@ class BenchMouseRegionMixedGridHover extends WidgetRecorder {
   void frameDidDraw() {
     if (!started) {
       started = true;
-      SchedulerBinding.instance!.addPostFrameCallback((Duration timeStamp) async {
+      SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) async {
         _tester.start();
         registerDidStop(_tester.stop);
       });
@@ -146,7 +146,7 @@ class _UntilNextFrame {
   static Future<void> wait() {
     if (_UntilNextFrame._completer == null) {
       _UntilNextFrame._completer = Completer<void>();
-      SchedulerBinding.instance!.addPostFrameCallback((_) {
+      SchedulerBinding.instance.addPostFrameCallback((_) {
         _UntilNextFrame._completer!.complete(null);
         _UntilNextFrame._completer = null;
       });
@@ -167,7 +167,7 @@ class _Tester {
   TestGesture get gesture {
     return _gesture ??= TestGesture(
       dispatcher: (PointerEvent event) async {
-        RendererBinding.instance!.handlePointerEvent(event);
+        RendererBinding.instance.handlePointerEvent(event);
       },
       kind: PointerDeviceKind.mouse,
     );

dev/benchmarks/macrobenchmarks/lib/src/web/recorder.dart

@@ -935,7 +935,7 @@ double _computeAverage(String label, Iterable<double> values) {
 ///
 /// See also:
 ///
-/// * https://en.wikipedia.org/wiki/Standard_deviation
+///  * <https://en.wikipedia.org/wiki/Standard_deviation>
 double _computeStandardDeviationForPopulation(String label, Iterable<double> population) {
   if (population.isEmpty) {
     throw StateError('$label: attempted to compute the standard deviation of empty population.');
@@ -987,12 +987,32 @@ class _RecordingWidgetsBinding extends BindingBase
         SemanticsBinding,
         RendererBinding,
         WidgetsBinding {
-  /// Makes an instance of [_RecordingWidgetsBinding] the current binding.
+
+  @override
+  void initInstances() {
+    super.initInstances();
+    _instance = this;
+  }
+
+  /// The singleton instance of this object.
+  ///
+  /// Provides access to the features exposed by this class. The binding must
+  /// be initialized before using this getter; this is typically done by calling
+  /// [_RecordingWidgetsBinding.ensureInitialized].
+  static _RecordingWidgetsBinding get instance => BindingBase.checkInstance(_instance);
+  static _RecordingWidgetsBinding? _instance;
+
+  /// Returns an instance of the [_RecordingWidgetsBinding], creating and
+  /// initializing it if necessary.
+  ///
+  /// See also:
+  ///
+  ///  * [WidgetsFlutterBinding.ensureInitialized], the equivalent in the widgets framework.
   static _RecordingWidgetsBinding ensureInitialized() {
-    if (WidgetsBinding.instance == null) {
+    if (_instance == null) {
       _RecordingWidgetsBinding();
     }
-    return WidgetsBinding.instance! as _RecordingWidgetsBinding;
+    return instance;
   }
 
   FrameRecorder? _recorder;

dev/benchmarks/macrobenchmarks/test/frame_policy.dart

@@ -10,8 +10,7 @@ import 'package:integration_test/integration_test.dart';
 import 'package:macrobenchmarks/src/simple_scroll.dart';
 
 void main() {
-  final IntegrationTestWidgetsFlutterBinding binding =
+  final IntegrationTestWidgetsFlutterBinding binding = IntegrationTestWidgetsFlutterBinding.ensureInitialized();
-      IntegrationTestWidgetsFlutterBinding.ensureInitialized() as IntegrationTestWidgetsFlutterBinding;
   testWidgets(
     'Frame Counter and Input Delay for benchmarkLive',
     (WidgetTester tester) async {

dev/benchmarks/macrobenchmarks/test_memory/heavy_gridview.dart

@@ -10,8 +10,8 @@ import 'package:macrobenchmarks/main.dart';
 
 Future<void> endOfAnimation() async {
   do {
-    await SchedulerBinding.instance!.endOfFrame;
+    await SchedulerBinding.instance.endOfFrame;
-  } while (SchedulerBinding.instance!.hasScheduledFrame);
+  } while (SchedulerBinding.instance.hasScheduledFrame);
 }
 
 Future<void> main() async {

dev/benchmarks/macrobenchmarks/test_memory/large_images.dart

@@ -10,8 +10,8 @@ import 'package:macrobenchmarks/main.dart';
 
 Future<void> endOfAnimation() async {
   do {
-    await SchedulerBinding.instance!.endOfFrame;
+    await SchedulerBinding.instance.endOfFrame;
-  } while (SchedulerBinding.instance!.hasScheduledFrame);
+  } while (SchedulerBinding.instance.hasScheduledFrame);
 }
 
 Future<void> main() async {

dev/benchmarks/microbenchmarks/lib/foundation/all_elements_bench.dart

@@ -44,24 +44,24 @@ Future<void> main() async {
 
   // Wait for frame rendering to stabilize.
   for (int i = 0; i < 5; i++) {
-    await SchedulerBinding.instance?.endOfFrame;
+    await SchedulerBinding.instance.endOfFrame;
   }
 
   final Stopwatch watch = Stopwatch();
 
-  print('flutter_test allElements benchmark... (${WidgetsBinding.instance?.renderViewElement})');
+  print('flutter_test allElements benchmark... (${WidgetsBinding.instance.renderViewElement})');
   // Make sure we get enough elements to process for consistent benchmark runs
-  int elementCount = collectAllElementsFrom(WidgetsBinding.instance!.renderViewElement!, skipOffstage: false).length;
+  int elementCount = collectAllElementsFrom(WidgetsBinding.instance.renderViewElement!, skipOffstage: false).length;
   while (elementCount < 2458) {
     await Future<void>.delayed(Duration.zero);
-    elementCount = collectAllElementsFrom(WidgetsBinding.instance!.renderViewElement!, skipOffstage: false).length;
+    elementCount = collectAllElementsFrom(WidgetsBinding.instance.renderViewElement!, skipOffstage: false).length;
   }
   print('element count: $elementCount');
 
   watch.start();
   for (int i = 0; i < _kNumIters; i += 1) {
     final List<Element> allElements = collectAllElementsFrom(
-      WidgetsBinding.instance!.renderViewElement!,
+      WidgetsBinding.instance.renderViewElement!,
       skipOffstage: false,
     ).toList();
     allElements.clear();

dev/benchmarks/microbenchmarks/lib/stocks/animation_bench.dart

@@ -68,7 +68,7 @@ Future<void> main() async {
 
       // Time how long each frame takes
       cpuWatch.reset();
-      while (SchedulerBinding.instance!.hasScheduledFrame) {
+      while (SchedulerBinding.instance.hasScheduledFrame) {
         await tester.pump();
         totalSubsequentFramesIterationCount += 1;
       }

dev/benchmarks/microbenchmarks/lib/stocks/layout_bench.dart

@@ -33,18 +33,18 @@ Future<void> main() async {
 
     final TestViewConfiguration big = TestViewConfiguration(
       size: const Size(360.0, 640.0),
-      window: RendererBinding.instance?.window,
+      window: RendererBinding.instance.window,
     );
     final TestViewConfiguration small = TestViewConfiguration(
       size: const Size(355.0, 635.0),
-      window: RendererBinding.instance?.window,
+      window: RendererBinding.instance.window,
     );
-    final RenderView? renderView = WidgetsBinding.instance?.renderView;
+    final RenderView renderView = WidgetsBinding.instance.renderView;
     binding.framePolicy = LiveTestWidgetsFlutterBindingFramePolicy.benchmark;
 
     watch.start();
     while (watch.elapsed < kBenchmarkTime) {
-      renderView?.configuration = iterations.isEven ? big : small;
+      renderView.configuration = iterations.isEven ? big : small;
       await tester.pumpBenchmark(Duration(milliseconds: iterations * 16));
       iterations += 1;
     }

dev/integration_tests/abstract_method_smoke_test/lib/main.dart

@@ -42,7 +42,7 @@ class _HomePage extends State<HomePage> {
 
     // Trigger the second route.
     // https://github.com/flutter/flutter/issues/40126
-    WidgetsBinding.instance?.addPostFrameCallback((_) async {
+    WidgetsBinding.instance.addPostFrameCallback((_) async {
       Navigator.of(context).push(
           MaterialPageRoute<void>(builder: (_) => const SecondPage()));
     });

dev/integration_tests/flutter_gallery/test/calculator/smoke_test.dart

@@ -7,7 +7,7 @@ import 'package:flutter_gallery/demo/calculator_demo.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
-  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized() as TestWidgetsFlutterBinding;
+  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized();
   if (binding is LiveTestWidgetsFlutterBinding)
     binding.framePolicy = LiveTestWidgetsFlutterBindingFramePolicy.fullyLive;
 

dev/integration_tests/flutter_gallery/test/drawer_test.dart

@@ -8,7 +8,7 @@ import 'package:flutter_gallery/gallery/app.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
-  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized() as TestWidgetsFlutterBinding;
+  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized();
   if (binding is LiveTestWidgetsFlutterBinding)
     binding.framePolicy = LiveTestWidgetsFlutterBindingFramePolicy.fullyLive;
 

dev/integration_tests/flutter_gallery/test/example_code_display_test.dart

@@ -7,7 +7,7 @@ import 'package:flutter_gallery/gallery/app.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
-  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized() as TestWidgetsFlutterBinding;
+  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized();
   if (binding is LiveTestWidgetsFlutterBinding)
     binding.framePolicy = LiveTestWidgetsFlutterBindingFramePolicy.fullyLive;
 

dev/integration_tests/flutter_gallery/test/live_smoketest.dart

@@ -58,7 +58,7 @@ Future<void> main() async {
 
     print('Starting app...');
     runApp(const GalleryApp(testMode: true));
-    final _LiveWidgetController controller = _LiveWidgetController(WidgetsBinding.instance!);
+    final _LiveWidgetController controller = _LiveWidgetController(WidgetsBinding.instance);
     for (final GalleryDemoCategory category in kAllGalleryDemoCategories) {
       print('Tapping "${category.name}" section...');
       await controller.tap(find.text(category.name));
@@ -111,7 +111,7 @@ class _LiveWidgetController extends LiveWidgetController {
   Future<void> _waitUntilFrame(bool Function() condition, [Completer<void>? completer]) {
     completer ??= Completer<void>();
     if (!condition()) {
-      SchedulerBinding.instance!.addPostFrameCallback((Duration timestamp) {
+      SchedulerBinding.instance.addPostFrameCallback((Duration timestamp) {
         _waitUntilFrame(condition, completer);
       });
     } else {

dev/integration_tests/flutter_gallery/test/pesto_test.dart

@@ -7,7 +7,7 @@ import 'package:flutter_gallery/gallery/app.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
-  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized() as TestWidgetsFlutterBinding;
+  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized();
   if (binding is LiveTestWidgetsFlutterBinding)
     binding.framePolicy = LiveTestWidgetsFlutterBindingFramePolicy.fullyLive;
 

dev/integration_tests/flutter_gallery/test/simple_smoke_test.dart

@@ -7,7 +7,7 @@ import 'package:flutter_gallery/gallery/app.dart' show GalleryApp;
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
-  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized() as TestWidgetsFlutterBinding;
+  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized();
   if (binding is LiveTestWidgetsFlutterBinding)
     binding.framePolicy = LiveTestWidgetsFlutterBindingFramePolicy.fullyLive;
 

dev/integration_tests/flutter_gallery/test/smoke_test.dart

@@ -77,9 +77,9 @@ Future<void> smokeDemo(WidgetTester tester, GalleryDemo demo) async {
 
   // Verify that the dumps are pretty.
   final String routeName = demo.routeName;
-  verifyToStringOutput('debugDumpApp', routeName, WidgetsBinding.instance!.renderViewElement!.toStringDeep());
+  verifyToStringOutput('debugDumpApp', routeName, WidgetsBinding.instance.renderViewElement!.toStringDeep());
-  verifyToStringOutput('debugDumpRenderTree', routeName, RendererBinding.instance?.renderView.toStringDeep() ?? '');
+  verifyToStringOutput('debugDumpRenderTree', routeName, RendererBinding.instance.renderView.toStringDeep());
-  verifyToStringOutput('debugDumpLayerTree', routeName, RendererBinding.instance?.renderView.debugLayer?.toStringDeep() ?? '');
+  verifyToStringOutput('debugDumpLayerTree', routeName, RendererBinding.instance.renderView.debugLayer?.toStringDeep() ?? '');
 
   // Scroll the demo around a bit more.
   await tester.flingFrom(const Offset(400.0, 300.0), const Offset(0.0, 400.0), 1000.0);
@@ -179,8 +179,8 @@ void main() {
   testWidgets('Flutter Gallery app smoke test', smokeGallery);
 
   testWidgets('Flutter Gallery app smoke test with semantics', (WidgetTester tester) async {
-    RendererBinding.instance!.setSemanticsEnabled(true);
+    RendererBinding.instance.setSemanticsEnabled(true);
     await smokeGallery(tester);
-    RendererBinding.instance!.setSemanticsEnabled(false);
+    RendererBinding.instance.setSemanticsEnabled(false);
   });
 }

dev/integration_tests/flutter_gallery/test/update_test.dart

@@ -11,7 +11,7 @@ Future<String> mockUpdateUrlFetcher() {
 }
 
 void main() {
-  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized() as TestWidgetsFlutterBinding;
+  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized();
   if (binding is LiveTestWidgetsFlutterBinding)
     binding.framePolicy = LiveTestWidgetsFlutterBindingFramePolicy.fullyLive;
 

dev/integration_tests/flutter_gallery/test_driver/transitions_perf.dart

@@ -30,12 +30,12 @@ class _MessageHandler {
       case 'demoNames':
         return const JsonEncoder.withIndent('  ').convert(_allDemos);
       case 'profileDemos':
-        controller ??= LiveWidgetController(WidgetsBinding.instance!);
+        controller ??= LiveWidgetController(WidgetsBinding.instance);
         await runDemos(kProfiledDemos, controller!);
         _unTestedDemos.removeAll(kProfiledDemos);
         return const JsonEncoder.withIndent('  ').convert(kProfiledDemos);
       case 'restDemos':
-        controller ??= LiveWidgetController(WidgetsBinding.instance!);
+        controller ??= LiveWidgetController(WidgetsBinding.instance);
         final List<String> restDemos =  _unTestedDemos.toList();
         await runDemos(restDemos, controller!);
         return const JsonEncoder.withIndent('  ').convert(restDemos);

dev/integration_tests/flutter_gallery/test_driver/transitions_perf_e2e.dart

@@ -22,8 +22,7 @@ List<String> _allDemos = kAllGalleryDemos.map(
 
 void main([List<String> args = const <String>[]]) {
   final bool withSemantics = args.contains('--with_semantics');
-  final IntegrationTestWidgetsFlutterBinding binding =
+  final IntegrationTestWidgetsFlutterBinding binding = IntegrationTestWidgetsFlutterBinding.ensureInitialized();
-      IntegrationTestWidgetsFlutterBinding.ensureInitialized() as IntegrationTestWidgetsFlutterBinding;
   binding.framePolicy = LiveTestWidgetsFlutterBindingFramePolicy.fullyLive;
   group('flutter gallery transitions on e2e', () {
     testWidgets('find.bySemanticsLabel', (WidgetTester tester) async {

dev/integration_tests/flutter_gallery/test_memory/back_button.dart

@@ -11,8 +11,8 @@ import 'package:flutter_test/flutter_test.dart';
 
 Future<void> endOfAnimation() async {
   do {
-    await SchedulerBinding.instance!.endOfFrame;
+    await SchedulerBinding.instance.endOfFrame;
-  } while (SchedulerBinding.instance!.hasScheduledFrame);
+  } while (SchedulerBinding.instance.hasScheduledFrame);
 }
 
 int iteration = 0;
@@ -30,5 +30,5 @@ Future<void> main() async {
   await endOfAnimation();
   await Future<void>.delayed(const Duration(milliseconds: 50));
   debugPrint('==== MEMORY BENCHMARK ==== READY ====');
-  WidgetsBinding.instance!.addObserver(LifecycleObserver());
+  WidgetsBinding.instance.addObserver(LifecycleObserver());
 }

dev/integration_tests/flutter_gallery/test_memory/image_cache_memory.dart

@@ -38,7 +38,7 @@ Future<void> main() async {
     ),
   ));
 
-  await SchedulerBinding.instance!.endOfFrame;
+  await SchedulerBinding.instance.endOfFrame;
 
   // We are waiting for the GPU to rasterize a frame here. This makes this
   // flaky, we can rely on a more deterministic source such as
@@ -48,7 +48,7 @@ Future<void> main() async {
   debugPrint('==== MEMORY BENCHMARK ==== READY ====');
 
   final WidgetController controller =
-      LiveWidgetController(WidgetsBinding.instance!);
+      LiveWidgetController(WidgetsBinding.instance);
 
   debugPrint('Scrolling...');
   final Finder list = find.byKey(const Key('ImageList'));

dev/integration_tests/flutter_gallery/test_memory/memory_nav.dart

@@ -13,8 +13,8 @@ import 'package:flutter_test/flutter_test.dart';
 
 Future<void> endOfAnimation() async {
   do {
-    await SchedulerBinding.instance!.endOfFrame;
+    await SchedulerBinding.instance.endOfFrame;
-  } while (SchedulerBinding.instance!.hasScheduledFrame);
+  } while (SchedulerBinding.instance.hasScheduledFrame);
 }
 
 Rect boundsFor(WidgetController controller, Finder item) {
@@ -35,7 +35,7 @@ Future<void> main() async {
       child: GalleryApp(testMode: true),
     ),
   ));
-  await SchedulerBinding.instance!.endOfFrame;
+  await SchedulerBinding.instance.endOfFrame;
   await Future<void>.delayed(const Duration(milliseconds: 50));
   debugPrint('==== MEMORY BENCHMARK ==== READY ====');
 
@@ -49,9 +49,9 @@ Future<void> main() async {
       child: GalleryApp(testMode: true),
     ),
   ));
-  await SchedulerBinding.instance!.endOfFrame;
+  await SchedulerBinding.instance.endOfFrame;
 
-  final WidgetController controller = LiveWidgetController(WidgetsBinding.instance!);
+  final WidgetController controller = LiveWidgetController(WidgetsBinding.instance);
 
   debugPrint('Navigating...');
   await controller.tap(find.text('Material'));

dev/integration_tests/ios_add2app_life_cycle/flutterapp/lib/main.dart

@@ -16,7 +16,7 @@ void main() {
   // Disconnects semantics listener for testing purposes.
   originalSemanticsListener = ui.window.onSemanticsEnabledChanged;
   ui.window.onSemanticsEnabledChanged = null;
-  RendererBinding.instance?.setSemanticsEnabled(false);
+  RendererBinding.instance.setSemanticsEnabled(false);
   // If the test passes, LifeCycleSpy will rewire the semantics listener back.
   runApp(const LifeCycleSpy());
 }
@@ -46,15 +46,15 @@ class _LifeCycleSpyState extends State<LifeCycleSpy> with WidgetsBindingObserver
   @override
   void initState() {
     super.initState();
-    WidgetsBinding.instance?.addObserver(this);
+    WidgetsBinding.instance.addObserver(this);
     _actualLifeCycleSequence =  <AppLifecycleState?>[
-      ServicesBinding.instance?.lifecycleState
+      ServicesBinding.instance.lifecycleState
     ];
   }
 
   @override
   void dispose() {
-    WidgetsBinding.instance?.removeObserver(this);
+    WidgetsBinding.instance.removeObserver(this);
     super.dispose();
   }
 
@@ -70,7 +70,7 @@ class _LifeCycleSpyState extends State<LifeCycleSpy> with WidgetsBindingObserver
   Widget build(BuildContext context) {
     if (const ListEquality<AppLifecycleState?>().equals(_actualLifeCycleSequence, _expectedLifeCycleSequence)) {
       // Rewires the semantics harness if test passes.
-      RendererBinding.instance?.setSemanticsEnabled(true);
+      RendererBinding.instance.setSemanticsEnabled(true);
       ui.window.onSemanticsEnabledChanged = originalSemanticsListener;
     }
     return const MaterialApp(

dev/manual_tests/lib/text.dart

@@ -960,7 +960,7 @@ class _PaintingState extends State<Painting> with SingleTickerProviderStateMixin
       }
       _text = buffer.toString();
     });
-    SchedulerBinding.instance?.addPostFrameCallback((Duration duration) {
+    SchedulerBinding.instance.addPostFrameCallback((Duration duration) {
       if (mounted && intrinsicKey.currentContext?.size?.height != controlKey.currentContext?.size?.height) {
         debugPrint('Found some text that unexpectedly renders at different heights.');
         debugPrint('Text: $_text');

dev/tracing_tests/test/image_cache_tracing_test.dart

@@ -32,18 +32,18 @@ void main() {
   test('Image cache tracing', () async {
     final TestImageStreamCompleter completer1 = TestImageStreamCompleter();
     final TestImageStreamCompleter completer2 = TestImageStreamCompleter();
-    PaintingBinding.instance!.imageCache!.putIfAbsent(
+    PaintingBinding.instance.imageCache.putIfAbsent(
       'Test',
       () => completer1,
     );
-    PaintingBinding.instance!.imageCache!.clear();
+    PaintingBinding.instance.imageCache.clear();
 
     completer2.testSetImage(ImageInfo(image: await createTestImage()));
-    PaintingBinding.instance!.imageCache!.putIfAbsent(
+    PaintingBinding.instance.imageCache.putIfAbsent(
       'Test2',
       () => completer2,
     );
-    PaintingBinding.instance!.imageCache!.evict('Test2');
+    PaintingBinding.instance.imageCache.evict('Test2');
 
     final Timeline timeline = await vmService.getVMTimeline();
     _expectTimelineEvents(

examples/layers/services/lifecycle.dart

@@ -18,12 +18,12 @@ class _LifecycleWatcherState extends State<LifecycleWatcher>
   @override
   void initState() {
     super.initState();
-    WidgetsBinding.instance!.addObserver(this);
+    WidgetsBinding.instance.addObserver(this);
   }
 
   @override
   void dispose() {
-    WidgetsBinding.instance!.removeObserver(this);
+    WidgetsBinding.instance.removeObserver(this);
     super.dispose();
   }
 

examples/layers/test/smoketests/rendering/custom_coordinate_systems_test.dart

@@ -13,6 +13,6 @@ void main() {
   test('layers smoketest for rendering/custom_coordinate_systems.dart', () {
     FlutterError.onError = (FlutterErrorDetails details) { throw details.exception; };
     demo.main();
-    expect(SchedulerBinding.instance!.hasScheduledFrame, true);
+    expect(SchedulerBinding.instance.hasScheduledFrame, true);
   });
 }

examples/layers/test/smoketests/rendering/flex_layout_test.dart

@@ -13,6 +13,6 @@ void main() {
   test('layers smoketest for rendering/flex_layout.dart', () {
     FlutterError.onError = (FlutterErrorDetails details) { throw details.exception; };
     demo.main();
-    expect(SchedulerBinding.instance!.hasScheduledFrame, true);
+    expect(SchedulerBinding.instance.hasScheduledFrame, true);
   });
 }

examples/layers/test/smoketests/rendering/hello_world_test.dart

@@ -13,6 +13,6 @@ void main() {
   test('layers smoketest for rendering/hello_world.dart', () {
     FlutterError.onError = (FlutterErrorDetails details) { throw details.exception; };
     demo.main();
-    expect(SchedulerBinding.instance!.hasScheduledFrame, true);
+    expect(SchedulerBinding.instance.hasScheduledFrame, true);
   });
 }

examples/layers/test/smoketests/rendering/spinning_square_test.dart

@@ -13,6 +13,6 @@ void main() {
   test('layers smoketest for rendering/spinning_square.dart', () {
     FlutterError.onError = (FlutterErrorDetails details) { throw details.exception; };
     demo.main();
-    expect(SchedulerBinding.instance!.hasScheduledFrame, true);
+    expect(SchedulerBinding.instance.hasScheduledFrame, true);
   });
 }

examples/layers/test/smoketests/rendering/touch_input_test.dart

@@ -13,6 +13,6 @@ void main() {
   test('layers smoketest for rendering/touch_input.dart', () {
     FlutterError.onError = (FlutterErrorDetails details) { throw details.exception; };
     demo.main();
-    expect(SchedulerBinding.instance!.hasScheduledFrame, true);
+    expect(SchedulerBinding.instance.hasScheduledFrame, true);
   });
 }

examples/layers/widgets/spinning_mixed.dart

@@ -73,7 +73,7 @@ void attachWidgetTreeToRenderTree(RenderProxyBox container) {
         ),
       ),
     ),
-  ).attachToRenderTree(WidgetsBinding.instance!.buildOwner!, element);
+  ).attachToRenderTree(WidgetsBinding.instance.buildOwner!, element);
 }
 
 Duration? timeBase;
@@ -86,7 +86,7 @@ void rotate(Duration timeStamp) {
   transformBox.setIdentity();
   transformBox.rotateZ(delta);
 
-  WidgetsBinding.instance!.buildOwner!.buildScope(element!);
+  WidgetsBinding.instance.buildOwner!.buildScope(element!);
 }
 
 void main() {

packages/flutter/lib/src/animation/animation_controller.dart

@@ -567,7 +567,7 @@ class AnimationController extends Animation<double>
 
   TickerFuture _animateToInternal(double target, { Duration? duration, Curve curve = Curves.linear }) {
     double scale = 1.0;
-    if (SemanticsBinding.instance!.disableAnimations) {
+    if (SemanticsBinding.instance.disableAnimations) {
       switch (animationBehavior) {
         case AnimationBehavior.normal:
           // Since the framework cannot handle zero duration animations, we run it at 5% of the normal
@@ -688,7 +688,7 @@ class AnimationController extends Animation<double>
                                          : upperBound + _kFlingTolerance.distance;
     double scale = 1.0;
     final AnimationBehavior behavior = animationBehavior ?? this.animationBehavior;
-    if (SemanticsBinding.instance!.disableAnimations) {
+    if (SemanticsBinding.instance.disableAnimations) {
       switch (behavior) {
         case AnimationBehavior.normal:
           // TODO(jonahwilliams): determine a better process for setting velocity.

packages/flutter/lib/src/cupertino/context_menu.dart

@@ -315,7 +315,7 @@ class _CupertinoContextMenuState extends State<CupertinoContextMenu> with Ticker
         // because _ContextMenuRoute renders its first frame offscreen.
         // Otherwise there would be a visible flash when nothing is rendered for
         // one frame.
-        SchedulerBinding.instance!.addPostFrameCallback((Duration _) {
+        SchedulerBinding.instance.addPostFrameCallback((Duration _) {
           _lastOverlayEntry?.remove();
           _lastOverlayEntry = null;
           _openController.reset();
@@ -742,7 +742,7 @@ class _ContextMenuRoute<T> extends PopupRoute<T> {
 
     // Render one frame offstage in the final position so that we can take
     // measurements of its layout and then animate to them.
-    SchedulerBinding.instance!.addPostFrameCallback((Duration _) {
+    SchedulerBinding.instance.addPostFrameCallback((Duration _) {
       _updateTweenRects();
       _internalOffstage = false;
       _setOffstageInternally();

packages/flutter/lib/src/cupertino/date_picker.dart

@@ -585,7 +585,7 @@ class _CupertinoDatePickerDateTimeState extends State<CupertinoDatePicker> {
     minuteController = FixedExtentScrollController(initialItem: initialDateTime.minute ~/ widget.minuteInterval);
     dateController = FixedExtentScrollController(initialItem: 0);
 
-    PaintingBinding.instance!.systemFonts.addListener(_handleSystemFontsChange);
+    PaintingBinding.instance.systemFonts.addListener(_handleSystemFontsChange);
   }
 
   void _handleSystemFontsChange () {
@@ -604,7 +604,7 @@ class _CupertinoDatePickerDateTimeState extends State<CupertinoDatePicker> {
     minuteController.dispose();
     meridiemController.dispose();
 
-    PaintingBinding.instance!.systemFonts.removeListener(_handleSystemFontsChange);
+    PaintingBinding.instance.systemFonts.removeListener(_handleSystemFontsChange);
     super.dispose();
   }
 
@@ -930,7 +930,7 @@ class _CupertinoDatePickerDateTimeState extends State<CupertinoDatePicker> {
 
   void _scrollToDate(DateTime newDate, DateTime fromDate) {
     assert(newDate != null);
-    SchedulerBinding.instance!.addPostFrameCallback((Duration timestamp) {
+    SchedulerBinding.instance.addPostFrameCallback((Duration timestamp) {
       if (fromDate.year != newDate.year || fromDate.month != newDate.month || fromDate.day != newDate.day) {
         _animateColumnControllerToItem(dateController, selectedDayFromInitial);
       }
@@ -1104,7 +1104,7 @@ class _CupertinoDatePickerDateState extends State<CupertinoDatePicker> {
     monthController = FixedExtentScrollController(initialItem: selectedMonth - 1);
     yearController = FixedExtentScrollController(initialItem: selectedYear);
 
-    PaintingBinding.instance!.systemFonts.addListener(_handleSystemFontsChange);
+    PaintingBinding.instance.systemFonts.addListener(_handleSystemFontsChange);
   }
 
   void _handleSystemFontsChange() {
@@ -1120,7 +1120,7 @@ class _CupertinoDatePickerDateState extends State<CupertinoDatePicker> {
     monthController.dispose();
     yearController.dispose();
 
-    PaintingBinding.instance!.systemFonts.removeListener(_handleSystemFontsChange);
+    PaintingBinding.instance.systemFonts.removeListener(_handleSystemFontsChange);
     super.dispose();
   }
 
@@ -1326,7 +1326,7 @@ class _CupertinoDatePickerDateState extends State<CupertinoDatePicker> {
 
   void _scrollToDate(DateTime newDate) {
     assert(newDate != null);
-    SchedulerBinding.instance!.addPostFrameCallback((Duration timestamp) {
+    SchedulerBinding.instance.addPostFrameCallback((Duration timestamp) {
       if (selectedYear != newDate.year) {
         _animateColumnControllerToItem(yearController, newDate.year);
       }
@@ -1608,7 +1608,7 @@ class _CupertinoTimerPickerState extends State<CupertinoTimerPicker> {
     if (widget.mode != CupertinoTimerPickerMode.hm)
       selectedSecond = widget.initialTimerDuration.inSeconds % 60;
 
-    PaintingBinding.instance!.systemFonts.addListener(_handleSystemFontsChange);
+    PaintingBinding.instance.systemFonts.addListener(_handleSystemFontsChange);
   }
 
   void _handleSystemFontsChange() {
@@ -1621,7 +1621,7 @@ class _CupertinoTimerPickerState extends State<CupertinoTimerPicker> {
 
   @override
   void dispose() {
-    PaintingBinding.instance!.systemFonts.removeListener(_handleSystemFontsChange);
+    PaintingBinding.instance.systemFonts.removeListener(_handleSystemFontsChange);
     super.dispose();
   }
 

packages/flutter/lib/src/cupertino/refresh.dart

@@ -506,10 +506,10 @@ class _CupertinoSliverRefreshControlState extends State<CupertinoSliverRefreshCo
       nextState = RefreshIndicatorMode.done;
       // Either schedule the RenderSliver to re-layout on the next frame
       // when not currently in a frame or schedule it on the next frame.
-      if (SchedulerBinding.instance!.schedulerPhase == SchedulerPhase.idle) {
+      if (SchedulerBinding.instance.schedulerPhase == SchedulerPhase.idle) {
         setState(() => hasSliverLayoutExtent = false);
       } else {
-        SchedulerBinding.instance!.addPostFrameCallback((Duration timestamp) {
+        SchedulerBinding.instance.addPostFrameCallback((Duration timestamp) {
           setState(() => hasSliverLayoutExtent = false);
         });
       }
@@ -535,7 +535,7 @@ class _CupertinoSliverRefreshControlState extends State<CupertinoSliverRefreshCo
             // Call onRefresh after this frame finished since the function is
             // user supplied and we're always here in the middle of the sliver's
             // performLayout.
-            SchedulerBinding.instance!.addPostFrameCallback((Duration timestamp) {
+            SchedulerBinding.instance.addPostFrameCallback((Duration timestamp) {
               refreshTask = widget.onRefresh!()..whenComplete(() {
                 if (mounted) {
                   setState(() => refreshTask = null);

packages/flutter/lib/src/foundation/README.md

@@ -7,6 +7,11 @@ Currently they do depend on dart:ui, but only for `VoidCallback` and
 `hashValues` (and maybe one day `hashList` and `lerpDouble`), which
 are all intended to be moved out of `dart:ui` and into `dart:core`.
 
+There is currently also an unfortunate dependency on the platform
+dispatcher logic (SingletonFlutterWindow, Brightness,
+PlatformDispatcher, window), though that should probably move to the
+'services' library.
+
 See also:
 
  * https://github.com/dart-lang/sdk/issues/27791 (`VoidCallback`)

packages/flutter/lib/src/foundation/binding.dart

@@ -14,10 +14,14 @@ import 'assertions.dart';
 import 'basic_types.dart';
 import 'constants.dart';
 import 'debug.dart';
+import 'diagnostics.dart';
 import 'object.dart';
 import 'platform.dart';
 import 'print.dart';
 
+// Examples can assume:
+// mixin BarBinding on BindingBase { }
+
 /// Signature for service extensions.
 ///
 /// The returned map must not contain the keys "type" or "method", as
@@ -27,21 +31,101 @@ import 'print.dart';
 /// "method" key will be set to the full name of the method.
 typedef ServiceExtensionCallback = Future<Map<String, dynamic>> Function(Map<String, String> parameters);
 
-/// Base class for mixins that provide singleton services (also known as
+/// Base class for mixins that provide singleton services.
-/// "bindings").
 ///
-/// To use this class in an `on` clause of a mixin, inherit from it and implement
+/// The Flutter engine ([dart:ui]) exposes some low-level services,
-/// [initInstances()]. The mixin is guaranteed to only be constructed once in
+/// but these are typically not suitable for direct use, for example
-/// the lifetime of the app (more precisely, it will assert if constructed twice
+/// because they only provide a single callback which an application
-/// in checked mode).
+/// may wish to multiplex to allow multiple listeners.
 ///
-/// The top-most layer used to write the application will have a concrete class
+/// Bindings provide the glue between these low-level APIs and the
-/// that inherits from [BindingBase] and uses all the various [BindingBase]
+/// higher-level framework APIs. They _bind_ the two together, whence
-/// mixins (such as [ServicesBinding]). For example, the Widgets library in
+/// the name.
-/// Flutter introduces a binding called [WidgetsFlutterBinding]. The relevant
+///
-/// library defines how to create the binding. It could be implied (for example,
+/// ## Implementing a binding mixin
-/// [WidgetsFlutterBinding] is automatically started from [runApp]), or the
+///
-/// application might be required to explicitly call the constructor.
+/// A library would typically create a new binding mixin to expose a
+/// feature in [dart:ui]. This is rare in general, but it is something
+/// that an alternative framework would do, e.g. if a framework were
+/// to replace the [widgets] library with an alternative API but still
+/// wished to leverage the [services] and [foundation] libraries.
+///
+/// To create a binding mixin, declare a mixin `on` the [BindingBase] class
+/// and whatever other bindings the concrete binding must implement for
+/// this binding mixin to be useful.
+///
+/// The mixin is guaranteed to only be constructed once in the
+/// lifetime of the app; this is handled by [initInstances].
+///
+/// A binding mixin must at a minimum implement the following features:
+///
+/// * The [initInstances] method, which must call `super.initInstances` and
+///   set an `_instance` static field to `this`.
+/// * An `instance` static getter, which must return that field using [checkInstance].
+///
+/// In addition, it should implement whatever singleton features the library needs.
+///
+/// As a general rule, the less can be placed in the binding, the
+/// better. Prefer having APIs that takes objects rather than having
+/// them refer to global singletons. Bindings are best limited to
+/// exposing features that literally only exist once, for example, the
+/// APIs in [dart:ui].
+///
+/// {@tool snippet}
+///
+/// Here is a basic example of a binding that implements these features. It relies on
+/// another fictional binding called `BarBinding`.
+///
+/// ```dart
+/// mixin FooBinding on BindingBase, BarBinding {
+///   @override
+///   void initInstances() {
+///     super.initInstances();
+///     _instance = this;
+///     // ...binding initialization...
+///   }
+///
+///   static FooBinding get instance => BindingBase.checkInstance(_instance);
+///   static FooBinding? _instance;
+///
+///   // ...binding features...
+/// }
+/// ```
+/// {@end-tool}
+///
+/// ## Implementing a binding class
+///
+/// The top-most layer used to write the application (e.g. the Flutter
+/// [widgets] library) will have a concrete class that inherits from
+/// [BindingBase] and uses all the various [BindingBase] mixins (such
+/// as [ServicesBinding]). The [widgets] library in Flutter introduces
+/// a binding called [WidgetsFlutterBinding].
+///
+/// A binding _class_ should mix in the relevant bindings from each
+/// layer that it wishes to expose, and should have an
+/// `ensureInitialized` method that constructs the class if that
+/// layer's mixin's `_instance` field is null. This allows the binding
+/// to be overriden by developers who have more specific needs, while
+/// still allowing other code to call `ensureInitialized` when a binding
+/// is needed.
+///
+/// {@tool snippet}
+///
+/// A typical binding class is shown below. The `ensureInitialized` method's
+/// return type is the library's binding mixin, rather than the concrete
+/// class.
+///
+/// ```dart
+/// class FooLibraryBinding extends BindingBase with BarBinding, FooBinding {
+///   static FooBinding ensureInitialized() {
+///     if (FooBinding._instance == null) {
+///       FooLibraryBinding();
+///     }
+///     return FooBinding.instance;
+///   }
+/// }
+/// /// ```
+/// {@end-tool}
 abstract class BindingBase {
   /// Default abstract constructor for bindings.
   ///
@@ -51,6 +135,10 @@ abstract class BindingBase {
   /// observatory service extensions, if any.
   BindingBase() {
     developer.Timeline.startSync('Framework initialization');
+    assert(() {
+      _debugConstructed = true;
+      return true;
+    }());
 
     assert(!_debugInitialized);
     initInstances();
@@ -65,6 +153,7 @@ abstract class BindingBase {
     developer.Timeline.finishSync();
   }
 
+  bool _debugConstructed = false;
   static bool _debugInitialized = false;
   static bool _debugServiceExtensionsRegistered = false;
 
@@ -131,10 +220,39 @@ abstract class BindingBase {
   /// the platform and otherwise configure their services. Subclasses must call
   /// "super.initInstances()".
   ///
-  /// By convention, if the service is to be provided as a singleton, it should
+  /// The binding is not fully initialized when this method runs (for
-  /// be exposed as `MixinClassName.instance`, a static getter that returns
+  /// example, other binding mixins may not yet have run their
+  /// [initInstances] method). For this reason, code in this method
+  /// should avoid invoking callbacks or synchronously triggering any
+  /// code that would normally assume that the bindings are ready.
+  ///
+  /// {@tool snippet}
+  ///
+  /// By convention, if the service is to be provided as a singleton,
+  /// it should be exposed as `MixinClassName.instance`, a static
+  /// getter with a non-nullable return type that returns
   /// `MixinClassName._instance`, a static field that is set by
-  /// `initInstances()`.
+  /// `initInstances()`. To improve the developer experience, the
+  /// return value should actually be
+  /// `BindingBase.checkInstance(_instance)` (see [checkInstance]), as
+  /// in the example below.
+  ///
+  /// ```dart
+  /// mixin BazBinding on BindingBase {
+  ///   @override
+  ///   void initInstances() {
+  ///     super.initInstances();
+  ///     _instance = this;
+  ///     // ...binding initialization...
+  ///   }
+  ///
+  ///   static BazBinding get instance => BindingBase.checkInstance(_instance);
+  ///   static BazBinding? _instance;
+  ///
+  ///   // ...binding features...
+  /// }
+  /// ```
+  /// {@end-tool}
   @protected
   @mustCallSuper
   void initInstances() {
@@ -145,6 +263,100 @@ abstract class BindingBase {
     }());
   }
 
+  /// A method that shows a useful error message if the given binding
+  /// instance is not initialized.
+  ///
+  /// See [initInstances] for advice on using this method.
+  ///
+  /// This method either returns the argument or throws an exception.
+  /// In release mode it always returns the argument.
+  ///
+  /// The type argument `T` should be the kind of binding mixin (e.g.
+  /// `SchedulerBinding`) that is calling the method. It is used in
+  /// error messages.
+  @protected
+  static T checkInstance<T extends BindingBase>(T? instance) {
+    assert(() {
+      if (!_debugInitialized && instance == null) {
+        throw FlutterError.fromParts(<DiagnosticsNode>[
+          ErrorSummary('Binding has not yet been initialized.'),
+          ErrorDescription('The "instance" getter on the $T binding mixin is only available once that binding has been initialized.'),
+          ErrorHint(
+            'Typically, this is done by calling "WidgetsFlutterBinding.ensureInitialized()" or "runApp()" (the '
+            'latter calls the former). Typically this call is done in the "void main()" method. The "ensureInitialized" method '
+            'is idempotent; calling it multiple times is not harmful. After calling that method, the "instance" getter will '
+            'return the binding.',
+          ),
+          ErrorHint(
+            'In a test, one can call "TestWidgetsFlutterBinding.ensureInitialized()" as the first line in the test\'s "main()" method '
+            'to initialize the binding.',
+          ),
+          ErrorHint(
+            'If $T is a custom binding mixin, there must also be a custom binding class, like WidgetsFlutterBinding, '
+            'but that mixes in the selected binding, and that is the class that must be constructed before using the "instance" getter.',
+          ),
+        ]);
+      }
+      if (instance == null) {
+        assert(_debugInitialized);
+        throw FlutterError.fromParts(<DiagnosticsNode>[
+          ErrorSummary('Binding mixin instance is null but bindings are already initialized.'),
+          ErrorDescription(
+            'The "instance" property of the $T binding mixin was accessed, but that binding was not initialized when '
+            'the "initInstances()" method was called.'
+          ),
+          ErrorHint(
+            'This probably indicates that the $T mixin was not mixed into the class that was used to initialize the binding. '
+            'If this is a custom binding mixin, there must also be a custom binding class, like WidgetsFlutterBinding, '
+            'but that mixes in the selected binding. If this is a test binding, check that the binding being initialized '
+            'is the same as the one into which the test binding is mixed.'
+          ),
+        ]);
+      }
+      try {
+        assert(instance != null);
+        if (instance._debugConstructed && !_debugInitialized) {
+          throw FlutterError.fromParts(<DiagnosticsNode>[
+            ErrorSummary('Binding initialized without calling initInstances.'),
+            ErrorDescription('An instance of $T is non-null, but BindingBase.initInstances() has not yet been called.'),
+            ErrorHint(
+              'This could happen because a binding mixin was somehow used outside of the normal binding mechanisms, or because '
+              'the binding\'s initInstances() method did not call "super.initInstances()".'
+            ),
+            ErrorHint(
+              'This could also happen if some code was invoked that used the binding while the binding was initializing, '
+              'for example if the "initInstances" method invokes a callback. Bindings should not invoke callbacks before '
+              '"initInstances" has completed.'
+            ),
+          ]);
+        }
+        if (!instance._debugConstructed) {
+          // The state of _debugInitialized doesn't matter in this failure mode.
+          throw FlutterError.fromParts(<DiagnosticsNode>[
+            ErrorSummary('Binding did not complete initialization.'),
+            ErrorDescription('An instance of $T is non-null, but the BindingBase() constructor has not yet been called.'),
+            ErrorHint(
+              'This could also happen if some code was invoked that used the binding while the binding was initializing, '
+              "for example if the binding's constructor itself invokes a callback. Bindings should not invoke callbacks "
+              'before "initInstances" has completed.'
+            ),
+          ]);
+        }
+      } on NoSuchMethodError {
+        throw FlutterError.fromParts(<DiagnosticsNode>[
+          ErrorSummary('Binding does not extend BindingBase'),
+          ErrorDescription('An instance of $T was created but the BindingBase constructor was not called.'),
+          ErrorHint(
+            'This could happen because the binding was implemented using "implements" rather than "extends" or "with". '
+            'Concrete binding classes must extend or mix in BindingBase.'
+          ),
+        ]);
+      }
+      return true;
+    }());
+    return instance!;
+  }
+
   /// Called when the binding is initialized, to register service
   /// extensions.
   ///
@@ -555,7 +767,7 @@ abstract class BindingBase {
   /// available in debug and profile mode.
   ///
   /// ```dart
-  /// void myRegistrationFunction() {
+  /// void myOtherRegistrationFunction() {
   ///   // kReleaseMode is defined in the 'flutter/foundation.dart' package.
   ///   if (!kReleaseMode) {
   ///     // Register your service extension here.

packages/flutter/lib/src/gestures/binding.dart

@@ -73,7 +73,7 @@ class _Resampler {
   // Add `event` for resampling or dispatch it directly if
   // not a touch event.
   void addOrDispatch(PointerEvent event) {
-    final SchedulerBinding? scheduler = SchedulerBinding.instance;
+    final SchedulerBinding scheduler = SchedulerBinding.instance;
     assert(scheduler != null);
     // Add touch event to resampler or dispatch pointer event directly.
     if (event.kind == PointerDeviceKind.touch) {
@@ -94,9 +94,10 @@ class _Resampler {
   //
   // The `samplingOffset` is relative to the current frame time, which
   // can be in the past when we're not actively resampling.
+  //
   // The `samplingClock` is the clock used to determine frame time age.
   void sample(Duration samplingOffset, SamplingClock clock) {
-    final SchedulerBinding? scheduler = SchedulerBinding.instance;
+    final SchedulerBinding scheduler = SchedulerBinding.instance;
     assert(scheduler != null);
 
     // Initialize `_frameTime` if needed. This will be used for periodic
@@ -156,7 +157,7 @@ class _Resampler {
       // Add a post frame callback as this avoids producing unnecessary
       // frames but ensures that sampling phase is adjusted to frame
       // time when frames are produced.
-      scheduler?.addPostFrameCallback((_) {
+      scheduler.addPostFrameCallback((_) {
         _frameCallbackScheduled = false;
         // We use `currentSystemFrameTimeStamp` here as it's critical that
         // sample time is in the same clock as the event time stamps, and
@@ -259,16 +260,20 @@ mixin GestureBinding on BindingBase implements HitTestable, HitTestDispatcher, H
     window.onPointerDataPacket = _handlePointerDataPacket;
   }
 
+  /// The singleton instance of this object.
+  ///
+  /// Provides access to the features exposed by this mixin. The binding must
+  /// be initialized before using this getter; this is typically done by calling
+  /// [runApp] or [WidgetsFlutterBinding.ensureInitialized].
+  static GestureBinding get instance => BindingBase.checkInstance(_instance);
+  static GestureBinding? _instance;
+
   @override
   void unlocked() {
     super.unlocked();
     _flushPointerEventQueue();
   }
 
-  /// The singleton instance of this object.
-  static GestureBinding? get instance => _instance;
-  static GestureBinding? _instance;
-
   final Queue<PointerEvent> _pendingPointerEvents = Queue<PointerEvent>();
 
   void _handlePointerDataPacket(ui.PointerDataPacket packet) {

packages/flutter/lib/src/gestures/multidrag.dart

@@ -231,8 +231,8 @@ abstract class MultiDragGestureRecognizer extends GestureRecognizer {
     assert(!_pointers!.containsKey(event.pointer));
     final MultiDragPointerState state = createNewPointerState(event);
     _pointers![event.pointer] = state;
-    GestureBinding.instance!.pointerRouter.addRoute(event.pointer, _handleEvent);
+    GestureBinding.instance.pointerRouter.addRoute(event.pointer, _handleEvent);
-    state._setArenaEntry(GestureBinding.instance!.gestureArena.add(event.pointer, this));
+    state._setArenaEntry(GestureBinding.instance.gestureArena.add(event.pointer, this));
   }
 
   /// Subclasses should override this method to create per-pointer state
@@ -312,7 +312,7 @@ abstract class MultiDragGestureRecognizer extends GestureRecognizer {
       return;
     }
     assert(_pointers!.containsKey(pointer));
-    GestureBinding.instance!.pointerRouter.removeRoute(pointer, _handleEvent);
+    GestureBinding.instance.pointerRouter.removeRoute(pointer, _handleEvent);
     _pointers!.remove(pointer)!.dispose();
   }
 

packages/flutter/lib/src/gestures/multitap.dart

@@ -79,14 +79,14 @@ class _TapTracker {
   void startTrackingPointer(PointerRoute route, Matrix4? transform) {
     if (!_isTrackingPointer) {
       _isTrackingPointer = true;
-      GestureBinding.instance!.pointerRouter.addRoute(pointer, route, transform);
+      GestureBinding.instance.pointerRouter.addRoute(pointer, route, transform);
     }
   }
 
   void stopTrackingPointer(PointerRoute route) {
     if (_isTrackingPointer) {
       _isTrackingPointer = false;
-      GestureBinding.instance!.pointerRouter.removeRoute(pointer, route);
+      GestureBinding.instance.pointerRouter.removeRoute(pointer, route);
     }
   }
 
@@ -242,7 +242,7 @@ class DoubleTapGestureRecognizer extends GestureRecognizer {
     _stopDoubleTapTimer();
     final _TapTracker tracker = _TapTracker(
       event: event,
-      entry: GestureBinding.instance!.gestureArena.add(event.pointer, this),
+      entry: GestureBinding.instance.gestureArena.add(event.pointer, this),
       doubleTapMinTime: kDoubleTapMinTime,
     );
     _trackers[event.pointer] = tracker;
@@ -311,14 +311,14 @@ class DoubleTapGestureRecognizer extends GestureRecognizer {
       final _TapTracker tracker = _firstTap!;
       _firstTap = null;
       _reject(tracker);
-      GestureBinding.instance!.gestureArena.release(tracker.pointer);
+      GestureBinding.instance.gestureArena.release(tracker.pointer);
     }
     _clearTrackers();
   }
 
   void _registerFirstTap(_TapTracker tracker) {
     _startDoubleTapTimer();
-    GestureBinding.instance!.gestureArena.hold(tracker.pointer);
+    GestureBinding.instance.gestureArena.hold(tracker.pointer);
     // Note, order is important below in order for the clear -> reject logic to
     // work properly.
     _freezeTracker(tracker);
@@ -383,7 +383,7 @@ class _TapGesture extends _TapTracker {
   }) : _lastPosition = OffsetPair.fromEventPosition(event),
        super(
     event: event as PointerDownEvent,
-    entry: GestureBinding.instance!.gestureArena.add(event.pointer, gestureRecognizer),
+    entry: GestureBinding.instance.gestureArena.add(event.pointer, gestureRecognizer),
     doubleTapMinTime: kDoubleTapMinTime,
   ) {
     startTrackingPointer(handleEvent, event.transform);

packages/flutter/lib/src/gestures/pointer_signal_resolver.dart

@@ -30,7 +30,7 @@ bool _isSameEvent(PointerSignalEvent event1, PointerSignalEvent event2) {
 ///
 /// ```dart
 /// void handleSignalEvent(PointerSignalEvent event) {
-///   GestureBinding.instance!.pointerSignalResolver.register(event, (PointerSignalEvent event) {
+///   GestureBinding.instance.pointerSignalResolver.register(event, (PointerSignalEvent event) {
 ///     // handle the event...
 ///   });
 /// }
@@ -96,7 +96,7 @@ bool _isSameEvent(PointerSignalEvent event1, PointerSignalEvent event2) {
 ///       child: Listener(
 ///         onPointerSignal: (PointerSignalEvent event) {
 ///           if (widget.useResolver) {
-///             GestureBinding.instance!.pointerSignalResolver.register(event, (PointerSignalEvent event) {
+///             GestureBinding.instance.pointerSignalResolver.register(event, (PointerSignalEvent event) {
 ///               rotateColor();
 ///             });
 ///           } else {

packages/flutter/lib/src/gestures/recognizer.dart

@@ -317,7 +317,7 @@ abstract class OneSequenceGestureRecognizer extends GestureRecognizer {
   void dispose() {
     resolve(GestureDisposition.rejected);
     for (final int pointer in _trackedPointers)
-      GestureBinding.instance!.pointerRouter.removeRoute(pointer, handleEvent);
+      GestureBinding.instance.pointerRouter.removeRoute(pointer, handleEvent);
     _trackedPointers.clear();
     assert(_entries.isEmpty);
     super.dispose();
@@ -347,7 +347,7 @@ abstract class OneSequenceGestureRecognizer extends GestureRecognizer {
   GestureArenaEntry _addPointerToArena(int pointer) {
     if (_team != null)
       return _team!.add(pointer, this);
-    return GestureBinding.instance!.gestureArena.add(pointer, this);
+    return GestureBinding.instance.gestureArena.add(pointer, this);
   }
 
   /// Causes events related to the given pointer ID to be routed to this recognizer.
@@ -366,7 +366,7 @@ abstract class OneSequenceGestureRecognizer extends GestureRecognizer {
   /// This is called by [OneSequenceGestureRecognizer.addAllowedPointer].
   @protected
   void startTrackingPointer(int pointer, [Matrix4? transform]) {
-    GestureBinding.instance!.pointerRouter.addRoute(pointer, handleEvent, transform);
+    GestureBinding.instance.pointerRouter.addRoute(pointer, handleEvent, transform);
     _trackedPointers.add(pointer);
     assert(!_entries.containsValue(pointer));
     _entries[pointer] = _addPointerToArena(pointer);
@@ -381,7 +381,7 @@ abstract class OneSequenceGestureRecognizer extends GestureRecognizer {
   @protected
   void stopTrackingPointer(int pointer) {
     if (_trackedPointers.contains(pointer)) {
-      GestureBinding.instance!.pointerRouter.removeRoute(pointer, handleEvent);
+      GestureBinding.instance.pointerRouter.removeRoute(pointer, handleEvent);
       _trackedPointers.remove(pointer);
       if (_trackedPointers.isEmpty)
         didStopTrackingLastPointer(pointer);

packages/flutter/lib/src/gestures/team.dart

@@ -61,7 +61,7 @@ class _CombiningGestureArenaMember extends GestureArenaMember {
     assert(!_resolved);
     assert(_pointer == pointer);
     _members.add(member);
-    _entry ??= GestureBinding.instance!.gestureArena.add(pointer, this);
+    _entry ??= GestureBinding.instance.gestureArena.add(pointer, this);
     return _CombiningGestureArenaEntry(this, member);
   }
 

packages/flutter/lib/src/material/about.dart

@@ -844,7 +844,7 @@ class _PackageLicensePageState extends State<_PackageLicensePage> {
         return true;
       }());
       final List<LicenseParagraph> paragraphs =
-        await SchedulerBinding.instance!.scheduleTask<List<LicenseParagraph>>(
+        await SchedulerBinding.instance.scheduleTask<List<LicenseParagraph>>(
           license.paragraphs.toList,
           Priority.animation,
           debugLabel: 'License',
@@ -1507,15 +1507,13 @@ class _MasterDetailScaffoldState extends State<_MasterDetailScaffold>
 
   @override
   void openDetailPage(Object arguments) {
-    SchedulerBinding.instance!
+    SchedulerBinding.instance.addPostFrameCallback((_) => _detailArguments.value = arguments);
-        .addPostFrameCallback((_) => _detailArguments.value = arguments);
     _MasterDetailFlow.of(context)!.openDetailPage(arguments);
   }
 
   @override
   void setInitialDetailPage(Object arguments) {
-    SchedulerBinding.instance!
+    SchedulerBinding.instance.addPostFrameCallback((_) => _detailArguments.value = arguments);
-        .addPostFrameCallback((_) => _detailArguments.value = arguments);
     _MasterDetailFlow.of(context)!.setInitialDetailPage(arguments);
   }
 

packages/flutter/lib/src/material/autocomplete.dart

@@ -301,7 +301,7 @@ class _AutocompleteOptions<T extends Object> extends StatelessWidget {
                   builder: (BuildContext context) {
                     final bool highlight = AutocompleteHighlightedOption.of(context) == index;
                     if (highlight) {
-                      SchedulerBinding.instance!.addPostFrameCallback((Duration timeStamp) {
+                      SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) {
                         Scrollable.ensureVisible(context, alignment: 0.5);
                       });
                     }

packages/flutter/lib/src/material/calendar_date_picker.dart

@@ -533,7 +533,7 @@ class _MonthPickerState extends State<_MonthPicker> {
     super.didUpdateWidget(oldWidget);
     if (widget.initialMonth != oldWidget.initialMonth && widget.initialMonth != _currentMonth) {
       // We can't interrupt this widget build with a scroll, so do it next frame
-      WidgetsBinding.instance!.addPostFrameCallback(
+      WidgetsBinding.instance.addPostFrameCallback(
         (Duration timeStamp) => _showMonth(widget.initialMonth, jump: true),
       );
     }

packages/flutter/lib/src/material/dropdown.dart

@@ -1237,16 +1237,16 @@ class _DropdownButtonState<T> extends State<DropdownButton<T>> with WidgetsBindi
       ),
     };
     focusNode!.addListener(_handleFocusChanged);
-    final FocusManager focusManager = WidgetsBinding.instance!.focusManager;
+    final FocusManager focusManager = WidgetsBinding.instance.focusManager;
     _focusHighlightMode = focusManager.highlightMode;
     focusManager.addHighlightModeListener(_handleFocusHighlightModeChange);
   }
 
   @override
   void dispose() {
-    WidgetsBinding.instance!.removeObserver(this);
+    WidgetsBinding.instance.removeObserver(this);
     _removeDropdownRoute();
-    WidgetsBinding.instance!.focusManager.removeHighlightModeListener(_handleFocusHighlightModeChange);
+    WidgetsBinding.instance.focusManager.removeHighlightModeListener(_handleFocusHighlightModeChange);
     focusNode!.removeListener(_handleFocusChanged);
     _internalNode?.dispose();
     super.dispose();

packages/flutter/lib/src/material/input_date_picker_form_field.dart

@@ -161,7 +161,7 @@ class _InputDatePickerFormFieldState extends State<InputDatePickerFormField> {
     super.didUpdateWidget(oldWidget);
     if (widget.initialDate != oldWidget.initialDate) {
       // Can't update the form field in the middle of a build, so do it next frame
-      WidgetsBinding.instance!.addPostFrameCallback((Duration timeStamp) {
+      WidgetsBinding.instance.addPostFrameCallback((Duration timeStamp) {
         setState(() {
           _selectedDate = widget.initialDate;
           _updateValueForSelectedDate();

packages/flutter/lib/src/material/time_picker.dart

@@ -833,7 +833,7 @@ class _DialPainter extends CustomPainter {
     required this.theta,
     required this.textDirection,
     required this.selectedValue,
-  }) : super(repaint: PaintingBinding.instance!.systemFonts);
+  }) : super(repaint: PaintingBinding.instance.systemFonts);
 
   final List<_TappableLabel> primaryLabels;
   final List<_TappableLabel> secondaryLabels;

packages/flutter/lib/src/material/tooltip.dart

@@ -269,7 +269,7 @@ class _TooltipState extends State<Tooltip> with SingleTickerProviderStateMixin {
   @override
   void initState() {
     super.initState();
-    _mouseIsConnected = RendererBinding.instance!.mouseTracker.mouseIsConnected;
+    _mouseIsConnected = RendererBinding.instance.mouseTracker.mouseIsConnected;
     _controller = AnimationController(
       duration: _fadeInDuration,
       reverseDuration: _fadeOutDuration,
@@ -277,10 +277,10 @@ class _TooltipState extends State<Tooltip> with SingleTickerProviderStateMixin {
     )
       ..addStatusListener(_handleStatusChanged);
     // Listen to see when a mouse is added.
-    RendererBinding.instance!.mouseTracker.addListener(_handleMouseTrackerChange);
+    RendererBinding.instance.mouseTracker.addListener(_handleMouseTrackerChange);
     // Listen to global pointer events so that we can hide a tooltip immediately
     // if some other control is clicked on.
-    GestureBinding.instance!.pointerRouter.addGlobalRoute(_handlePointerEvent);
+    GestureBinding.instance.pointerRouter.addGlobalRoute(_handlePointerEvent);
   }
 
   // https://material.io/components/tooltips#specs
@@ -325,7 +325,7 @@ class _TooltipState extends State<Tooltip> with SingleTickerProviderStateMixin {
     if (!mounted) {
       return;
     }
-    final bool mouseIsConnected = RendererBinding.instance!.mouseTracker.mouseIsConnected;
+    final bool mouseIsConnected = RendererBinding.instance.mouseTracker.mouseIsConnected;
     if (mouseIsConnected != _mouseIsConnected) {
       setState(() {
         _mouseIsConnected = mouseIsConnected;
@@ -456,8 +456,8 @@ class _TooltipState extends State<Tooltip> with SingleTickerProviderStateMixin {
 
   @override
   void dispose() {
-    GestureBinding.instance!.pointerRouter.removeGlobalRoute(_handlePointerEvent);
+    GestureBinding.instance.pointerRouter.removeGlobalRoute(_handlePointerEvent);
-    RendererBinding.instance!.mouseTracker.removeListener(_handleMouseTrackerChange);
+    RendererBinding.instance.mouseTracker.removeListener(_handleMouseTrackerChange);
     _removeEntry();
     _controller.dispose();
     super.dispose();

packages/flutter/lib/src/painting/_network_image_io.dart

@@ -118,7 +118,7 @@ class NetworkImage extends image_provider.ImageProvider<image_provider.NetworkIm
       // have had a chance to track the key in the cache at all.
       // Schedule a microtask to give the cache a chance to add the key.
       scheduleMicrotask(() {
-        PaintingBinding.instance!.imageCache!.evict(key);
+        PaintingBinding.instance.imageCache.evict(key);
       });
       rethrow;
     } finally {

packages/flutter/lib/src/painting/binding.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-
 import 'dart:typed_data' show Uint8List;
 import 'dart:ui' as ui show instantiateImageCodec, Codec;
 import 'package:flutter/foundation.dart';
@@ -26,7 +25,11 @@ mixin PaintingBinding on BindingBase, ServicesBinding {
   }
 
   /// The current [PaintingBinding], if one has been created.
-  static PaintingBinding? get instance => _instance;
+  ///
+  /// Provides access to the features exposed by this mixin. The binding must
+  /// be initialized before using this getter; this is typically done by calling
+  /// [runApp] or [WidgetsFlutterBinding.ensureInitialized].
+  static PaintingBinding get instance => BindingBase.checkInstance(_instance);
   static PaintingBinding? _instance;
 
   /// [ShaderWarmUp] instance to be executed during [initInstances].
@@ -67,8 +70,8 @@ mixin PaintingBinding on BindingBase, ServicesBinding {
   ///
   /// The image cache is created during startup by the [createImageCache]
   /// method.
-  ImageCache? get imageCache => _imageCache;
+  ImageCache get imageCache => _imageCache;
-  ImageCache? _imageCache;
+  late ImageCache _imageCache;
 
   /// Creates the [ImageCache] singleton (accessible via [imageCache]).
   ///
@@ -114,14 +117,14 @@ mixin PaintingBinding on BindingBase, ServicesBinding {
   @override
   void evict(String asset) {
     super.evict(asset);
-    imageCache!.clear();
+    imageCache.clear();
-    imageCache!.clearLiveImages();
+    imageCache.clearLiveImages();
   }
 
   @override
   void handleMemoryPressure() {
     super.handleMemoryPressure();
-    imageCache?.clear();
+    imageCache.clear();
   }
 
   /// Listenable that notifies when the available fonts on the system have
@@ -176,4 +179,4 @@ class _SystemFontsNotifier extends Listenable {
 ///
 /// The image cache is created during startup by the [PaintingBinding]'s
 /// [PaintingBinding.createImageCache] method.
-ImageCache? get imageCache => PaintingBinding.instance!.imageCache;
+ImageCache get imageCache => PaintingBinding.instance.imageCache;

packages/flutter/lib/src/painting/decoration_image.dart

@@ -539,7 +539,7 @@ void paintImage({
         _pendingImageSizeInfo[sizeInfo.source!] = sizeInfo;
       }
       debugOnPaintImage?.call(sizeInfo);
-      SchedulerBinding.instance!.addPostFrameCallback((Duration timeStamp) {
+      SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) {
         _lastFrameImageSizeInfo = _pendingImageSizeInfo.values.toSet();
         if (_pendingImageSizeInfo.isEmpty) {
           return;

packages/flutter/lib/src/painting/image_cache.dart

@@ -622,7 +622,7 @@ abstract class _CachedImageBase {
     assert(handle != null);
     // Give any interested parties a chance to listen to the stream before we
     // potentially dispose it.
-    SchedulerBinding.instance!.addPostFrameCallback((Duration timeStamp) {
+    SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) {
       assert(handle != null);
       handle?.dispose();
       handle = null;

packages/flutter/lib/src/painting/image_decoder.dart

@@ -21,7 +21,7 @@ import 'binding.dart';
 /// [PaintingBinding.instantiateImageCodec], and therefore can be mocked in
 /// tests.
 Future<ui.Image> decodeImageFromList(Uint8List bytes) async {
-  final ui.Codec codec = await PaintingBinding.instance!.instantiateImageCodec(bytes);
+  final ui.Codec codec = await PaintingBinding.instance.instantiateImageCodec(bytes);
   final ui.FrameInfo frameInfo = await codec.getNextFrame();
   return frameInfo.image;
 }

packages/flutter/lib/src/painting/image_provider.dart

@@ -387,7 +387,7 @@ abstract class ImageProvider<T extends Object> {
     _createErrorHandlerAndKey(
       configuration,
       (T key, ImageErrorListener innerHandleError) {
-        completer.complete(PaintingBinding.instance!.imageCache!.statusForKey(key));
+        completer.complete(PaintingBinding.instance.imageCache.statusForKey(key));
       },
       (T? key, Object exception, StackTrace? stack) async {
         if (handleError != null) {
@@ -492,7 +492,7 @@ abstract class ImageProvider<T extends Object> {
     // the image we want before getting to this method. We should avoid calling
     // load again, but still update the image cache with LRU information.
     if (stream.completer != null) {
-      final ImageStreamCompleter? completer = PaintingBinding.instance!.imageCache!.putIfAbsent(
+      final ImageStreamCompleter? completer = PaintingBinding.instance.imageCache.putIfAbsent(
         key,
         () => stream.completer!,
         onError: handleError,
@@ -500,9 +500,9 @@ abstract class ImageProvider<T extends Object> {
       assert(identical(completer, stream.completer));
       return;
     }
-    final ImageStreamCompleter? completer = PaintingBinding.instance!.imageCache!.putIfAbsent(
+    final ImageStreamCompleter? completer = PaintingBinding.instance.imageCache.putIfAbsent(
       key,
-      () => load(key, PaintingBinding.instance!.instantiateImageCodec),
+      () => load(key, PaintingBinding.instance.instantiateImageCodec),
       onError: handleError,
     );
     if (completer != null) {
@@ -557,7 +557,7 @@ abstract class ImageProvider<T extends Object> {
   Future<bool> evict({ ImageCache? cache, ImageConfiguration configuration = ImageConfiguration.empty }) async {
     cache ??= imageCache;
     final T key = await obtainKey(configuration);
-    return cache!.evict(key);
+    return cache.evict(key);
   }
 
   /// Converts an ImageProvider's settings plus an ImageConfiguration to a key
@@ -674,11 +674,11 @@ abstract class AssetBundleImageProvider extends ImageProvider<AssetBundleImageKe
     try {
       data = await key.bundle.load(key.name);
     } on FlutterError {
-      PaintingBinding.instance!.imageCache!.evict(key);
+      PaintingBinding.instance.imageCache.evict(key);
       rethrow;
     }
     if (data == null) {
-      PaintingBinding.instance!.imageCache!.evict(key);
+      PaintingBinding.instance.imageCache.evict(key);
       throw StateError('Unable to read data');
     }
     return decode(data.buffer.asUint8List());
@@ -891,7 +891,7 @@ class FileImage extends ImageProvider<FileImage> {
 
     if (bytes.lengthInBytes == 0) {
       // The file may become available later.
-      PaintingBinding.instance!.imageCache!.evict(key);
+      PaintingBinding.instance.imageCache.evict(key);
       throw StateError('$file is empty and cannot be loaded as an image.');
     }
 

packages/flutter/lib/src/painting/image_stream.dart

@@ -964,7 +964,7 @@ class MultiFrameImageStreamCompleter extends ImageStreamCompleter {
       return;
     }
     _frameCallbackScheduled = true;
-    SchedulerBinding.instance!.scheduleFrameCallback(_handleAppFrame);
+    SchedulerBinding.instance.scheduleFrameCallback(_handleAppFrame);
   }
 
   void _emitFrame(ImageInfo imageInfo) {

packages/flutter/lib/src/rendering/binding.dart

@@ -49,7 +49,11 @@ mixin RendererBinding on BindingBase, ServicesBinding, SchedulerBinding, Gesture
   }
 
   /// The current [RendererBinding], if one has been created.
-  static RendererBinding? get instance => _instance;
+  ///
+  /// Provides access to the features exposed by this mixin. The binding must
+  /// be initialized before using this getter; this is typically done by calling
+  /// [runApp] or [WidgetsFlutterBinding.ensureInitialized].
+  static RendererBinding get instance => BindingBase.checkInstance(_instance);
   static RendererBinding? _instance;
 
   @override
@@ -114,7 +118,7 @@ mixin RendererBinding on BindingBase, ServicesBinding, SchedulerBinding, Gesture
       registerServiceExtension(
         name: 'debugDumpLayerTree',
         callback: (Map<String, String> parameters) async {
-          final String data = RendererBinding.instance?.renderView.debugLayer?.toStringDeep() ?? 'Layer tree unavailable.';
+          final String data = RendererBinding.instance.renderView.debugLayer?.toStringDeep() ?? 'Layer tree unavailable.';
           return <String, Object>{
             'data': data,
           };
@@ -128,7 +132,7 @@ mixin RendererBinding on BindingBase, ServicesBinding, SchedulerBinding, Gesture
       registerServiceExtension(
         name: 'debugDumpRenderTree',
         callback: (Map<String, String> parameters) async {
-          final String data = RendererBinding.instance?.renderView.toStringDeep() ?? 'Render tree unavailable.';
+          final String data = RendererBinding.instance.renderView.toStringDeep();
           return <String, Object>{
             'data': data,
           };
@@ -138,7 +142,7 @@ mixin RendererBinding on BindingBase, ServicesBinding, SchedulerBinding, Gesture
       registerServiceExtension(
         name: 'debugDumpSemanticsTreeInTraversalOrder',
         callback: (Map<String, String> parameters) async {
-          final String data = RendererBinding.instance?.renderView.debugSemantics
+          final String data = RendererBinding.instance.renderView.debugSemantics
             ?.toStringDeep(childOrder: DebugSemanticsDumpOrder.traversalOrder) ?? 'Semantics not collected.';
           return <String, Object>{
             'data': data,
@@ -149,7 +153,7 @@ mixin RendererBinding on BindingBase, ServicesBinding, SchedulerBinding, Gesture
       registerServiceExtension(
         name: 'debugDumpSemanticsTreeInInverseHitTestOrder',
         callback: (Map<String, String> parameters) async {
-          final String data = RendererBinding.instance?.renderView.debugSemantics
+          final String data = RendererBinding.instance.renderView.debugSemantics
             ?.toStringDeep(childOrder: DebugSemanticsDumpOrder.inverseHitTest) ?? 'Semantics not collected.';
           return <String, Object>{
             'data': data,
@@ -229,7 +233,7 @@ mixin RendererBinding on BindingBase, ServicesBinding, SchedulerBinding, Gesture
   /// Querying [PlatformDispatcher.platformBrightness].
   ///
   /// ```dart
-  /// final Brightness brightness = WidgetsBinding.instance!.platformDispatcher.platformBrightness;
+  /// final Brightness brightness = WidgetsBinding.instance.platformDispatcher.platformBrightness;
   /// ```
   /// {@end-tool}
   ///
@@ -338,7 +342,7 @@ mixin RendererBinding on BindingBase, ServicesBinding, SchedulerBinding, Gesture
       _debugMouseTrackerUpdateScheduled = true;
       return true;
     }());
-    SchedulerBinding.instance!.addPostFrameCallback((Duration duration) {
+    SchedulerBinding.instance.addPostFrameCallback((Duration duration) {
       assert(_debugMouseTrackerUpdateScheduled);
       assert(() {
         _debugMouseTrackerUpdateScheduled = false;
@@ -501,19 +505,19 @@ mixin RendererBinding on BindingBase, ServicesBinding, SchedulerBinding, Gesture
       child.markNeedsPaint();
       child.visitChildren(visitor);
     };
-    instance?.renderView.visitChildren(visitor);
+    instance.renderView.visitChildren(visitor);
     return endOfFrame;
   }
 }
 
 /// Prints a textual representation of the entire render tree.
 void debugDumpRenderTree() {
-  debugPrint(RendererBinding.instance?.renderView.toStringDeep() ?? 'Render tree unavailable.');
+  debugPrint(RendererBinding.instance.renderView.toStringDeep());
 }
 
 /// Prints a textual representation of the entire layer tree.
 void debugDumpLayerTree() {
-  debugPrint(RendererBinding.instance?.renderView.debugLayer?.toStringDeep() ?? 'Layer tree unavailable.');
+  debugPrint(RendererBinding.instance.renderView.debugLayer?.toStringDeep());
 }
 
 /// Prints a textual representation of the entire semantics tree.
@@ -523,16 +527,27 @@ void debugDumpLayerTree() {
 /// The order in which the children of a [SemanticsNode] will be printed is
 /// controlled by the [childOrder] parameter.
 void debugDumpSemanticsTree(DebugSemanticsDumpOrder childOrder) {
-  debugPrint(RendererBinding.instance?.renderView.debugSemantics?.toStringDeep(childOrder: childOrder) ?? 'Semantics not collected.');
+  debugPrint(RendererBinding.instance.renderView.debugSemantics?.toStringDeep(childOrder: childOrder) ?? 'Semantics not collected.');
 }
 
 /// A concrete binding for applications that use the Rendering framework
 /// directly. This is the glue that binds the framework to the Flutter engine.
 ///
+/// When using the rendering framework directly, this binding, or one that
+/// implements the same interfaces, must be used. The following
+/// mixins are used to implement this binding:
+///
+/// * [GestureBinding], which implements the basics of hit testing.
+/// * [SchedulerBinding], which introduces the concepts of frames.
+/// * [ServicesBinding], which provides access to the plugin subsystem.
+/// * [SemanticsBinding], which supports accessibility.
+/// * [PaintingBinding], which enables decoding images.
+/// * [RendererBinding], which handles the render tree.
+///
 /// You would only use this binding if you are writing to the
 /// rendering layer directly. If you are writing to a higher-level
 /// library, such as the Flutter Widgets library, then you would use
-/// that layer's binding.
+/// that layer's binding (see [WidgetsFlutterBinding]).
 class RenderingFlutterBinding extends BindingBase with GestureBinding, SchedulerBinding, ServicesBinding, SemanticsBinding, PaintingBinding, RendererBinding {
   /// Creates a binding for the rendering layer.
   ///
@@ -545,4 +560,18 @@ class RenderingFlutterBinding extends BindingBase with GestureBinding, Scheduler
     assert(renderView != null);
     renderView.child = root;
   }
+
+  /// Returns an instance of the binding that implements
+  /// [RendererBinding]. If no binding has yet been initialized, the
+  /// [RenderingFlutterBinding] class is used to create and initialize
+  /// one.
+  ///
+  /// You need to call this method before using the rendering framework
+  /// if you are using it directly. If you are using the widgets framework,
+  /// see [WidgetsFlutterBinding.ensureInitialized].
+  static RendererBinding ensureInitialized() {
+    if (RendererBinding._instance == null)
+      RenderingFlutterBinding();
+    return RendererBinding.instance;
+  }
 }

packages/flutter/lib/src/rendering/object.dart

@@ -3498,12 +3498,12 @@ mixin RelayoutWhenSystemFontsChangeMixin on RenderObject {
   @override
   void attach(covariant PipelineOwner owner) {
     super.attach(owner);
-    PaintingBinding.instance!.systemFonts.addListener(systemFontsDidChange);
+    PaintingBinding.instance.systemFonts.addListener(systemFontsDidChange);
   }
 
   @override
   void detach() {
-    PaintingBinding.instance!.systemFonts.removeListener(systemFontsDidChange);
+    PaintingBinding.instance.systemFonts.removeListener(systemFontsDidChange);
     super.detach();
   }
 }

packages/flutter/lib/src/rendering/platform_view.dart

@@ -408,12 +408,12 @@ class RenderUiKitView extends RenderBox {
   @override
   void attach(PipelineOwner owner) {
     super.attach(owner);
-    GestureBinding.instance!.pointerRouter.addGlobalRoute(_handleGlobalPointerEvent);
+    GestureBinding.instance.pointerRouter.addGlobalRoute(_handleGlobalPointerEvent);
   }
 
   @override
   void detach() {
-    GestureBinding.instance!.pointerRouter.removeGlobalRoute(_handleGlobalPointerEvent);
+    GestureBinding.instance.pointerRouter.removeGlobalRoute(_handleGlobalPointerEvent);
     _gestureRecognizer!.reset();
     super.detach();
   }

packages/flutter/lib/src/scheduler/binding.dart

@@ -18,16 +18,18 @@ export 'dart:ui' show AppLifecycleState, VoidCallback, FrameTiming;
 /// Slows down animations by this factor to help in development.
 double get timeDilation => _timeDilation;
 double _timeDilation = 1.0;
-/// Setting the time dilation automatically calls [SchedulerBinding.resetEpoch]
+/// If the [SchedulerBinding] has been initialized, setting the time dilation
-/// to ensure that time stamps seen by consumers of the scheduler binding are
+/// automatically calls [SchedulerBinding.resetEpoch] to ensure that time stamps
-/// always increasing.
+/// seen by consumers of the scheduler binding are always increasing.
+///
+/// It is safe to set this before initializing the binding.
 set timeDilation(double value) {
   assert(value > 0.0);
   if (_timeDilation == value)
     return;
-  // We need to resetEpoch first so that we capture start of the epoch with the
+  // If the binding has been created, we need to resetEpoch first so that we
-  // current time dilation.
+  // capture start of the epoch with the current time dilation.
-  SchedulerBinding.instance?.resetEpoch();
+  SchedulerBinding._instance?.resetEpoch();
   _timeDilation = value;
 }
 
@@ -208,6 +210,14 @@ mixin SchedulerBinding on BindingBase {
     }
   }
 
+  /// The current [SchedulerBinding], if one has been created.
+  ///
+  /// Provides access to the features exposed by this mixin. The binding must
+  /// be initialized before using this getter; this is typically done by calling
+  /// [runApp] or [WidgetsFlutterBinding.ensureInitialized].
+  static SchedulerBinding get instance => BindingBase.checkInstance(_instance);
+  static SchedulerBinding? _instance;
+
   final List<TimingsCallback> _timingsCallbacks = <TimingsCallback>[];
 
   /// Add a [TimingsCallback] that receives [FrameTiming] sent from
@@ -307,10 +317,6 @@ mixin SchedulerBinding on BindingBase {
     }
   }
 
-  /// The current [SchedulerBinding], if one has been created.
-  static SchedulerBinding? get instance => _instance;
-  static SchedulerBinding? _instance;
-
   @override
   void initServiceExtensions() {
     super.initServiceExtensions();

packages/flutter/lib/src/scheduler/ticker.dart

@@ -113,9 +113,9 @@ class Ticker {
       return false;
     if (muted)
       return false;
-    if (SchedulerBinding.instance!.framesEnabled)
+    if (SchedulerBinding.instance.framesEnabled)
       return true;
-    if (SchedulerBinding.instance!.schedulerPhase != SchedulerPhase.idle)
+    if (SchedulerBinding.instance.schedulerPhase != SchedulerPhase.idle)
       return true; // for example, we might be in a warm-up frame or forced frame
     return false;
   }
@@ -161,9 +161,9 @@ class Ticker {
     if (shouldScheduleTick) {
       scheduleTick();
     }
-    if (SchedulerBinding.instance!.schedulerPhase.index > SchedulerPhase.idle.index &&
+    if (SchedulerBinding.instance.schedulerPhase.index > SchedulerPhase.idle.index &&
-        SchedulerBinding.instance!.schedulerPhase.index < SchedulerPhase.postFrameCallbacks.index)
+        SchedulerBinding.instance.schedulerPhase.index < SchedulerPhase.postFrameCallbacks.index)
-      _startTime = SchedulerBinding.instance!.currentFrameTimeStamp;
+      _startTime = SchedulerBinding.instance.currentFrameTimeStamp;
     return _future!;
   }
 
@@ -250,7 +250,7 @@ class Ticker {
   void scheduleTick({ bool rescheduling = false }) {
     assert(!scheduled);
     assert(shouldScheduleTick);
-    _animationId = SchedulerBinding.instance!.scheduleFrameCallback(_tick, rescheduling: rescheduling);
+    _animationId = SchedulerBinding.instance.scheduleFrameCallback(_tick, rescheduling: rescheduling);
   }
 
   /// Cancels the frame callback that was requested by [scheduleTick], if any.
@@ -262,7 +262,7 @@ class Ticker {
   @protected
   void unscheduleTick() {
     if (scheduled) {
-      SchedulerBinding.instance!.cancelFrameCallbackWithId(_animationId!);
+      SchedulerBinding.instance.cancelFrameCallbackWithId(_animationId!);
       _animationId = null;
     }
     assert(!shouldScheduleTick);

packages/flutter/lib/src/semantics/binding.dart

@@ -13,10 +13,6 @@ export 'dart:ui' show AccessibilityFeatures;
 /// The glue between the semantics layer and the Flutter engine.
 // TODO(jonahwilliams): move the remaining semantic related bindings here.
 mixin SemanticsBinding on BindingBase {
-  /// The current [SemanticsBinding], if one has been created.
-  static SemanticsBinding? get instance => _instance;
-  static SemanticsBinding? _instance;
-
   @override
   void initInstances() {
     super.initInstances();
@@ -24,6 +20,14 @@ mixin SemanticsBinding on BindingBase {
     _accessibilityFeatures = window.accessibilityFeatures;
   }
 
+  /// The current [SemanticsBinding], if one has been created.
+  ///
+  /// Provides access to the features exposed by this mixin. The binding must
+  /// be initialized before using this getter; this is typically done by calling
+  /// [runApp] or [WidgetsFlutterBinding.ensureInitialized].
+  static SemanticsBinding get instance => BindingBase.checkInstance(_instance);
+  static SemanticsBinding? _instance;
+
   /// Called when the platform accessibility features change.
   ///
   /// See [dart:ui.PlatformDispatcher.onAccessibilityFeaturesChanged].

packages/flutter/lib/src/semantics/semantics.dart

@@ -2938,7 +2938,7 @@ class SemanticsOwner extends ChangeNotifier {
       }
     }
     visitedNodes.sort((SemanticsNode a, SemanticsNode b) => a.depth - b.depth);
-    final ui.SemanticsUpdateBuilder builder = SemanticsBinding.instance!.createSemanticsUpdateBuilder();
+    final ui.SemanticsUpdateBuilder builder = SemanticsBinding.instance.createSemanticsUpdateBuilder();
     for (final SemanticsNode node in visitedNodes) {
       assert(node.parent?._dirty != true); // could be null (no parent) or false (not dirty)
       // The _serialize() method marks the node as not dirty, and
@@ -2959,7 +2959,7 @@ class SemanticsOwner extends ChangeNotifier {
       final CustomSemanticsAction action = CustomSemanticsAction.getAction(actionId)!;
       builder.updateCustomAction(id: actionId, label: action.label, hint: action.hint, overrideId: action.action?.index ?? -1);
     }
-    SemanticsBinding.instance!.window.updateSemantics(builder.build());
+    SemanticsBinding.instance.window.updateSemantics(builder.build());
     notifyListeners();
   }
 

packages/flutter/lib/src/services/asset_bundle.dart

@@ -219,7 +219,7 @@ class PlatformAssetBundle extends CachingAssetBundle {
   Future<ByteData> load(String key) async {
     final Uint8List encoded = utf8.encoder.convert(Uri(path: Uri.encodeFull(key)).path);
     final ByteData? asset =
-        await ServicesBinding.instance!.defaultBinaryMessenger.send('flutter/assets', encoded.buffer.asByteData());
+        await ServicesBinding.instance.defaultBinaryMessenger.send('flutter/assets', encoded.buffer.asByteData());
     if (asset == null)
       throw FlutterError('Unable to load asset: $key');
     return asset;

packages/flutter/lib/src/services/binding.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
@@ -39,7 +38,11 @@ mixin ServicesBinding on BindingBase, SchedulerBinding {
   }
 
   /// The current [ServicesBinding], if one has been created.
-  static ServicesBinding? get instance => _instance;
+  ///
+  /// Provides access to the features exposed by this mixin. The binding must
+  /// be initialized before using this getter; this is typically done by calling
+  /// [runApp] or [WidgetsFlutterBinding.ensureInitialized].
+  static ServicesBinding get instance => BindingBase.checkInstance(_instance);
   static ServicesBinding? _instance;
 
   /// The default instance of [BinaryMessenger].

packages/flutter/lib/src/services/platform_channel.dart

@@ -45,7 +45,7 @@ class BasicMessageChannel<T> {
   final MessageCodec<T> codec;
 
   /// The messenger which sends the bytes for this channel, not null.
-  BinaryMessenger get binaryMessenger => _binaryMessenger ?? ServicesBinding.instance!.defaultBinaryMessenger;
+  BinaryMessenger get binaryMessenger => _binaryMessenger ?? ServicesBinding.instance.defaultBinaryMessenger;
   final BinaryMessenger? _binaryMessenger;
 
   /// Sends the specified [message] to the platform plugins on this channel.
@@ -118,7 +118,7 @@ class MethodChannel {
   /// The messenger used by this channel to send platform messages.
   ///
   /// The messenger may not be null.
-  BinaryMessenger get binaryMessenger => _binaryMessenger ?? ServicesBinding.instance!.defaultBinaryMessenger;
+  BinaryMessenger get binaryMessenger => _binaryMessenger ?? ServicesBinding.instance.defaultBinaryMessenger;
   final BinaryMessenger? _binaryMessenger;
 
   /// Backend implementation of [invokeMethod].
@@ -450,7 +450,7 @@ class EventChannel {
   final MethodCodec codec;
 
   /// The messenger used by this channel to send platform messages, not null.
-  BinaryMessenger get binaryMessenger => _binaryMessenger ?? ServicesBinding.instance!.defaultBinaryMessenger;
+  BinaryMessenger get binaryMessenger => _binaryMessenger ?? ServicesBinding.instance.defaultBinaryMessenger;
   final BinaryMessenger? _binaryMessenger;
 
   /// Sets up a broadcast stream for receiving events on this channel.

packages/flutter/lib/src/services/restoration.dart

@@ -264,7 +264,7 @@ class RestorationManager extends ChangeNotifier {
 
     _isReplacing = _rootBucketIsValid && enabled;
     if (_isReplacing) {
-      SchedulerBinding.instance!.addPostFrameCallback((Duration _) {
+      SchedulerBinding.instance.addPostFrameCallback((Duration _) {
         _isReplacing = false;
       });
     }
@@ -350,7 +350,7 @@ class RestorationManager extends ChangeNotifier {
     _bucketsNeedingSerialization.add(bucket);
     if (!_serializationScheduled) {
       _serializationScheduled = true;
-      SchedulerBinding.instance!.addPostFrameCallback((Duration _) => _doSerialization());
+      SchedulerBinding.instance.addPostFrameCallback((Duration _) => _doSerialization());
     }
   }
 
@@ -413,7 +413,7 @@ class RestorationManager extends ChangeNotifier {
   /// current restoration data is directly sent to the engine.
   void flushData() {
     assert(!_debugDoingUpdate);
-    if (SchedulerBinding.instance!.hasScheduledFrame) {
+    if (SchedulerBinding.instance.hasScheduledFrame) {
       return;
     }
     _doSerialization();

packages/flutter/lib/src/services/system_chrome.dart

@@ -502,7 +502,7 @@ class SystemChrome {
   /// [SystemUiMode.leanBack].
   ///
   static Future<void> setSystemUIChangeCallback(SystemUiChangeCallback? callback) async {
-    ServicesBinding.instance!.setSystemUiChangeCallback(callback);
+    ServicesBinding.instance.setSystemUiChangeCallback(callback);
     // Skip setting up the listener if there is no callback.
     if (callback != null) {
       await SystemChannels.platform.invokeMethod<void>(

packages/flutter/lib/src/widgets/actions.dart

@@ -1324,7 +1324,7 @@ class _FocusableActionDetectorState extends State<FocusableActionDetector> {
   @override
   void initState() {
     super.initState();
-    SchedulerBinding.instance!.addPostFrameCallback((Duration duration) {
+    SchedulerBinding.instance.addPostFrameCallback((Duration duration) {
       _updateHighlightMode(FocusManager.instance.highlightMode);
     });
     FocusManager.instance.addHighlightModeListener(_handleFocusHighlightModeChange);
@@ -1413,7 +1413,7 @@ class _FocusableActionDetectorState extends State<FocusableActionDetector> {
       return _focused && _canShowHighlight && canRequestFocus(target);
     }
 
-    assert(SchedulerBinding.instance!.schedulerPhase != SchedulerPhase.persistentCallbacks);
+    assert(SchedulerBinding.instance.schedulerPhase != SchedulerPhase.persistentCallbacks);
     final FocusableActionDetector oldTarget = oldWidget ?? widget;
     final bool didShowHoverHighlight = shouldShowHoverHighlight(oldTarget);
     final bool didShowFocusHighlight = shouldShowFocusHighlight(oldTarget);
@@ -1434,7 +1434,7 @@ class _FocusableActionDetectorState extends State<FocusableActionDetector> {
   void didUpdateWidget(FocusableActionDetector oldWidget) {
     super.didUpdateWidget(oldWidget);
     if (widget.enabled != oldWidget.enabled) {
-      SchedulerBinding.instance!.addPostFrameCallback((Duration duration) {
+      SchedulerBinding.instance.addPostFrameCallback((Duration duration) {
         _mayTriggerCallback(oldWidget: oldWidget);
       });
     }

packages/flutter/lib/src/widgets/app.dart

@@ -1257,16 +1257,16 @@ class _WidgetsAppState extends State<WidgetsApp> with WidgetsBindingObserver {
   // If window.defaultRouteName isn't '/', we should assume it was set
   // intentionally via `setInitialRoute`, and should override whatever is in
   // [widget.initialRoute].
-  String get _initialRouteName => WidgetsBinding.instance!.window.defaultRouteName != Navigator.defaultRouteName
+  String get _initialRouteName => WidgetsBinding.instance.window.defaultRouteName != Navigator.defaultRouteName
-    ? WidgetsBinding.instance!.window.defaultRouteName
+    ? WidgetsBinding.instance.window.defaultRouteName
-    : widget.initialRoute ?? WidgetsBinding.instance!.window.defaultRouteName;
+    : widget.initialRoute ?? WidgetsBinding.instance.window.defaultRouteName;
 
   @override
   void initState() {
     super.initState();
     _updateRouting();
-    _locale = _resolveLocales(WidgetsBinding.instance!.window.locales, widget.supportedLocales);
+    _locale = _resolveLocales(WidgetsBinding.instance.window.locales, widget.supportedLocales);
-    WidgetsBinding.instance!.addObserver(this);
+    WidgetsBinding.instance.addObserver(this);
   }
 
   @override
@@ -1277,7 +1277,7 @@ class _WidgetsAppState extends State<WidgetsApp> with WidgetsBindingObserver {
 
   @override
   void dispose() {
-    WidgetsBinding.instance!.removeObserver(this);
+    WidgetsBinding.instance.removeObserver(this);
     _defaultRouteInformationProvider?.dispose();
     super.dispose();
   }
@@ -1681,7 +1681,7 @@ class _MediaQueryFromWindowsState extends State<_MediaQueryFromWindow> with Widg
   @override
   void initState() {
     super.initState();
-    WidgetsBinding.instance!.addObserver(this);
+    WidgetsBinding.instance.addObserver(this);
   }
 
   // ACCESSIBILITY
@@ -1725,7 +1725,7 @@ class _MediaQueryFromWindowsState extends State<_MediaQueryFromWindow> with Widg
 
   @override
   Widget build(BuildContext context) {
-    MediaQueryData data = MediaQueryData.fromWindow(WidgetsBinding.instance!.window);
+    MediaQueryData data = MediaQueryData.fromWindow(WidgetsBinding.instance.window);
     if (!kReleaseMode) {
       data = data.copyWith(platformBrightness: debugBrightnessOverride);
     }
@@ -1737,7 +1737,7 @@ class _MediaQueryFromWindowsState extends State<_MediaQueryFromWindow> with Widg
 
   @override
   void dispose() {
-    WidgetsBinding.instance!.removeObserver(this);
+    WidgetsBinding.instance.removeObserver(this);
     super.dispose();
   }
 }

packages/flutter/lib/src/widgets/autocomplete.dart

@@ -893,7 +893,7 @@ class _RawAutocompleteState<T extends Object> extends State<RawAutocomplete<T>>
       AutocompletePreviousOptionIntent: _previousOptionAction,
       AutocompleteNextOptionIntent: _nextOptionAction,
     };
-    SchedulerBinding.instance!.addPostFrameCallback((Duration _) {
+    SchedulerBinding.instance.addPostFrameCallback((Duration _) {
       _updateOverlay();
     });
   }
@@ -906,7 +906,7 @@ class _RawAutocompleteState<T extends Object> extends State<RawAutocomplete<T>>
       widget.textEditingController,
     );
     _updateFocusNode(oldWidget.focusNode, widget.focusNode);
-    SchedulerBinding.instance!.addPostFrameCallback((Duration _) {
+    SchedulerBinding.instance.addPostFrameCallback((Duration _) {
       _updateOverlay();
     });
   }

packages/flutter/lib/src/widgets/automatic_keep_alive.dart

@@ -89,7 +89,7 @@ class _AutomaticKeepAliveState extends State<AutomaticKeepAlive> {
         // If the child doesn't exist yet, we got called during the very first
         // build of this subtree. Wait until the end of the frame to update
         // the child when the child is guaranteed to be present.
-        SchedulerBinding.instance!.addPostFrameCallback((Duration timeStamp) {
+        SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) {
           if (!mounted) {
             return;
           }
@@ -155,7 +155,7 @@ class _AutomaticKeepAliveState extends State<AutomaticKeepAlive> {
       }());
       _handles!.remove(handle);
       if (_handles!.isEmpty) {
-        if (SchedulerBinding.instance!.schedulerPhase.index < SchedulerPhase.persistentCallbacks.index) {
+        if (SchedulerBinding.instance.schedulerPhase.index < SchedulerPhase.persistentCallbacks.index) {
           // Build/layout haven't started yet so let's just schedule this for
           // the next frame.
           setState(() { _keepingAlive = false; });

packages/flutter/lib/src/widgets/banner.dart

@@ -69,7 +69,7 @@ class BannerPainter extends CustomPainter {
        assert(location != null),
        assert(color != null),
        assert(textStyle != null),
-       super(repaint: PaintingBinding.instance!.systemFonts);
+       super(repaint: PaintingBinding.instance.systemFonts);
 
   /// The message to show in the banner.
   final String message;

packages/flutter/lib/src/widgets/binding.dart

@@ -50,12 +50,12 @@ export 'dart:ui' show AppLifecycleState, Locale;
 ///   @override
 ///   void initState() {
 ///     super.initState();
-///     WidgetsBinding.instance!.addObserver(this);
+///     WidgetsBinding.instance.addObserver(this);
 ///   }
 ///
 ///   @override
 ///   void dispose() {
-///     WidgetsBinding.instance!.removeObserver(this);
+///     WidgetsBinding.instance.removeObserver(this);
 ///     super.dispose();
 ///   }
 ///
@@ -147,19 +147,19 @@ abstract class WidgetsBindingObserver {
   ///   @override
   ///   void initState() {
   ///     super.initState();
-  ///     _lastSize = WidgetsBinding.instance!.window.physicalSize;
+  ///     _lastSize = WidgetsBinding.instance.window.physicalSize;
-  ///     WidgetsBinding.instance!.addObserver(this);
+  ///     WidgetsBinding.instance.addObserver(this);
   ///   }
   ///
   ///   @override
   ///   void dispose() {
-  ///     WidgetsBinding.instance!.removeObserver(this);
+  ///     WidgetsBinding.instance.removeObserver(this);
   ///     super.dispose();
   ///   }
   ///
   ///   @override
   ///   void didChangeMetrics() {
-  ///     setState(() { _lastSize = WidgetsBinding.instance!.window.physicalSize; });
+  ///     setState(() { _lastSize = WidgetsBinding.instance.window.physicalSize; });
   ///   }
   ///
   ///   @override
@@ -203,12 +203,12 @@ abstract class WidgetsBindingObserver {
   ///   @override
   ///   void initState() {
   ///     super.initState();
-  ///     WidgetsBinding.instance!.addObserver(this);
+  ///     WidgetsBinding.instance.addObserver(this);
   ///   }
   ///
   ///   @override
   ///   void dispose() {
-  ///     WidgetsBinding.instance!.removeObserver(this);
+  ///     WidgetsBinding.instance.removeObserver(this);
   ///     super.dispose();
   ///   }
   ///
@@ -216,7 +216,7 @@ abstract class WidgetsBindingObserver {
   ///
   ///   @override
   ///   void didChangeTextScaleFactor() {
-  ///     setState(() { _lastTextScaleFactor = WidgetsBinding.instance!.window.textScaleFactor; });
+  ///     setState(() { _lastTextScaleFactor = WidgetsBinding.instance.window.textScaleFactor; });
   ///   }
   ///
   ///   @override
@@ -296,6 +296,14 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
     }());
   }
 
+  /// The current [WidgetsBinding], if one has been created.
+  ///
+  /// Provides access to the features exposed by this mixin. The binding must
+  /// be initialized before using this getter; this is typically done by calling
+  /// [runApp] or [WidgetsFlutterBinding.ensureInitialized].
+  static WidgetsBinding get instance => BindingBase.checkInstance(_instance);
+  static WidgetsBinding? _instance;
+
   void _debugAddStackFilters() {
     const PartialStackFrame elementInflateWidget = PartialStackFrame(package: 'package:flutter/src/widgets/framework.dart', className: 'Element', method: 'inflateWidget');
     const PartialStackFrame elementUpdateChild = PartialStackFrame(package: 'package:flutter/src/widgets/framework.dart', className: 'Element', method: 'updateChild');
@@ -377,14 +385,6 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
     ));
   }
 
-  /// The current [WidgetsBinding], if one has been created.
-  ///
-  /// If you need the binding to be constructed before calling [runApp],
-  /// you can ensure a Widget binding has been constructed by calling the
-  /// `WidgetsFlutterBinding.ensureInitialized()` function.
-  static WidgetsBinding? get instance => _instance;
-  static WidgetsBinding? _instance;
-
   @override
   void initServiceExtensions() {
     super.initServiceExtensions();
@@ -862,14 +862,14 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
           developer.Timeline.instantSync('Rasterized first useful frame');
           developer.postEvent('Flutter.FirstFrame', <String, dynamic>{});
         }
-        SchedulerBinding.instance!.removeTimingsCallback(firstFrameCallback!);
+        SchedulerBinding.instance.removeTimingsCallback(firstFrameCallback!);
         firstFrameCallback = null;
         _firstFrameCompleter.complete();
       };
       // Callback is only invoked when FlutterView.render is called. When
       // sendFramesToEngine is set to false during the frame, it will not be
       // called and we need to remove the callback (see below).
-      SchedulerBinding.instance!.addTimingsCallback(firstFrameCallback!);
+      SchedulerBinding.instance.addTimingsCallback(firstFrameCallback!);
     }
 
     try {
@@ -893,7 +893,7 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
       // This frame is deferred and not the first frame sent to the engine that
       // should be reported.
       _needToReportFirstFrame = true;
-      SchedulerBinding.instance!.removeTimingsCallback(firstFrameCallback!);
+      SchedulerBinding.instance.removeTimingsCallback(firstFrameCallback!);
     }
   }
 
@@ -938,7 +938,7 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
       child: rootWidget,
     ).attachToRenderTree(buildOwner!, renderViewElement as RenderObjectToWidgetElement<RenderBox>?);
     if (isBootstrapFrame) {
-      SchedulerBinding.instance!.ensureVisualUpdate();
+      SchedulerBinding.instance.ensureVisualUpdate();
     }
   }
 
@@ -1033,12 +1033,11 @@ void runApp(Widget app) {
 }
 
 String _debugDumpAppString() {
-  assert(WidgetsBinding.instance != null);
+  const String mode = kDebugMode ? 'DEBUG MODE' : kReleaseMode ? 'RELEASE MODE' : 'PROFILE MODE';
-  const String mode = kDebugMode ? 'DEBUG MODE' : 'PROFILE MODE';
   final StringBuffer buffer = StringBuffer();
   buffer.writeln('${WidgetsBinding.instance.runtimeType} - $mode');
-  if (WidgetsBinding.instance!.renderViewElement != null) {
+  if (WidgetsBinding.instance.renderViewElement != null) {
-    buffer.writeln(WidgetsBinding.instance!.renderViewElement!.toStringDeep());
+    buffer.writeln(WidgetsBinding.instance.renderViewElement!.toStringDeep());
   } else {
     buffer.writeln('<no tree currently mounted>');
   }
@@ -1047,8 +1046,7 @@ String _debugDumpAppString() {
 
 /// Print a string representation of the currently running app.
 void debugDumpApp() {
-  final String value = _debugDumpAppString();
+  debugPrint(_debugDumpAppString());
-  debugPrint(value);
 }
 
 /// A bridge from a [RenderObject] to an [Element] tree.
@@ -1229,22 +1227,34 @@ class RenderObjectToWidgetElement<T extends RenderObject> extends RootRenderObje
 /// A concrete binding for applications based on the Widgets framework.
 ///
 /// This is the glue that binds the framework to the Flutter engine.
+///
+/// When using the widgets framework, this binding, or one that
+/// implements the same interfaces, must be used. The following
+/// mixins are used to implement this binding:
+///
+/// * [GestureBinding], which implements the basics of hit testing.
+/// * [SchedulerBinding], which introduces the concepts of frames.
+/// * [ServicesBinding], which provides access to the plugin subsystem.
+/// * [PaintingBinding], which enables decoding images.
+/// * [SemanticsBinding], which supports accessibility.
+/// * [RendererBinding], which handles the render tree.
+/// * [WidgetsBinding], which handles the widget tree.
 class WidgetsFlutterBinding extends BindingBase with GestureBinding, SchedulerBinding, ServicesBinding, PaintingBinding, SemanticsBinding, RendererBinding, WidgetsBinding {
-
+  /// Returns an instance of the binding that implements
-  /// Returns an instance of the [WidgetsBinding], creating and
+  /// [WidgetsBinding]. If no binding has yet been initialized, the
-  /// initializing it if necessary. If one is created, it will be a
+  /// [WidgetsFlutterBinding] class is used to create and initialize
-  /// [WidgetsFlutterBinding]. If one was previously initialized, then
+  /// one.
-  /// it will at least implement [WidgetsBinding].
   ///
   /// You only need to call this method if you need the binding to be
   /// initialized before calling [runApp].
   ///
   /// In the `flutter_test` framework, [testWidgets] initializes the
   /// binding instance to a [TestWidgetsFlutterBinding], not a
-  /// [WidgetsFlutterBinding].
+  /// [WidgetsFlutterBinding]. See
+  /// [TestWidgetsFlutterBinding.ensureInitialized].
   static WidgetsBinding ensureInitialized() {
-    if (WidgetsBinding.instance == null)
+    if (WidgetsBinding._instance == null)
       WidgetsFlutterBinding();
-    return WidgetsBinding.instance!;
+    return WidgetsBinding.instance;
   }
 }

packages/flutter/lib/src/widgets/drag_target.dart

@@ -919,7 +919,7 @@ class _DragAvatar<T extends Object> extends Drag {
     _lastOffset = globalPosition - dragStartPoint;
     _entry!.markNeedsBuild();
     final HitTestResult result = HitTestResult();
-    WidgetsBinding.instance!.hitTest(result, globalPosition + feedbackOffset);
+    WidgetsBinding.instance.hitTest(result, globalPosition + feedbackOffset);
 
     final List<_DragTargetState<Object>> targets = _getDragTargets(result.path).toList();
 

packages/flutter/lib/src/widgets/editable_text.dart

@@ -1625,7 +1625,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
 
     if (!_didAutoFocus && widget.autofocus) {
       _didAutoFocus = true;
-      SchedulerBinding.instance!.addPostFrameCallback((_) {
+      SchedulerBinding.instance.addPostFrameCallback((_) {
         if (mounted) {
           FocusScope.of(context).autofocus(widget.focusNode);
         }
@@ -1700,7 +1700,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
     _selectionOverlay = null;
     _focusAttachment!.detach();
     widget.focusNode.removeListener(_handleFocusChanged);
-    WidgetsBinding.instance!.removeObserver(this);
+    WidgetsBinding.instance.removeObserver(this);
     _clipboardStatus?.removeListener(_onChangedClipboardStatus);
     _clipboardStatus?.dispose();
     super.dispose();
@@ -2219,7 +2219,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
       return;
     }
     _showCaretOnScreenScheduled = true;
-    SchedulerBinding.instance!.addPostFrameCallback((Duration _) {
+    SchedulerBinding.instance.addPostFrameCallback((Duration _) {
       _showCaretOnScreenScheduled = false;
       if (_currentCaretRect == null || !_scrollController!.hasClients) {
         return;
@@ -2272,10 +2272,10 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
 
   @override
   void didChangeMetrics() {
-    if (_lastBottomViewInset < WidgetsBinding.instance!.window.viewInsets.bottom) {
+    if (_lastBottomViewInset < WidgetsBinding.instance.window.viewInsets.bottom) {
       _scheduleShowCaretOnScreen();
     }
-    _lastBottomViewInset = WidgetsBinding.instance!.window.viewInsets.bottom;
+    _lastBottomViewInset = WidgetsBinding.instance.window.viewInsets.bottom;
   }
 
   @pragma('vm:notify-debugger-on-exception')
@@ -2432,8 +2432,8 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
     _updateOrDisposeSelectionOverlayIfNeeded();
     if (_hasFocus) {
       // Listen for changing viewInsets, which indicates keyboard showing up.
-      WidgetsBinding.instance!.addObserver(this);
+      WidgetsBinding.instance.addObserver(this);
-      _lastBottomViewInset = WidgetsBinding.instance!.window.viewInsets.bottom;
+      _lastBottomViewInset = WidgetsBinding.instance.window.viewInsets.bottom;
       if (!widget.readOnly) {
         _scheduleShowCaretOnScreen();
       }
@@ -2442,7 +2442,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
         _handleSelectionChanged(TextSelection.collapsed(offset: _value.text.length), null);
       }
     } else {
-      WidgetsBinding.instance!.removeObserver(this);
+      WidgetsBinding.instance.removeObserver(this);
       // Clear the selection and composition state if this widget lost focus.
       _value = TextEditingValue(text: _value.text);
       _currentPromptRectRange = null;
@@ -2455,8 +2455,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
       final Size size = renderEditable.size;
       final Matrix4 transform = renderEditable.getTransformTo(null);
       _textInputConnection!.setEditableSizeAndTransform(size, transform);
-      SchedulerBinding.instance!
+      SchedulerBinding.instance.addPostFrameCallback((Duration _) => _updateSizeAndTransform());
-          .addPostFrameCallback((Duration _) => _updateSizeAndTransform());
     }
   }
 
@@ -2478,8 +2477,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
       }
       assert(composingRect != null);
       _textInputConnection!.setComposingRect(composingRect);
-      SchedulerBinding.instance!
+      SchedulerBinding.instance.addPostFrameCallback((Duration _) => _updateComposingRectIfNeeded());
-          .addPostFrameCallback((Duration _) => _updateComposingRectIfNeeded());
     }
   }
 
@@ -2491,8 +2489,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
         final Rect caretRect = renderEditable.getLocalRectForCaret(currentTextPosition);
         _textInputConnection!.setCaretRect(caretRect);
       }
-      SchedulerBinding.instance!
+      SchedulerBinding.instance.addPostFrameCallback((Duration _) => _updateCaretRectIfNeeded());
-          .addPostFrameCallback((Duration _) => _updateCaretRectIfNeeded());
     }
   }
 

packages/flutter/lib/src/widgets/focus_manager.dart

@@ -1465,21 +1465,21 @@ class FocusManager with DiagnosticableTreeMixin, ChangeNotifier {
   void registerGlobalHandlers() {
     assert(RawKeyboard.instance.keyEventHandler == null);
     RawKeyboard.instance.keyEventHandler = _handleRawKeyEvent;
-    GestureBinding.instance!.pointerRouter.addGlobalRoute(_handlePointerEvent);
+    GestureBinding.instance.pointerRouter.addGlobalRoute(_handlePointerEvent);
   }
 
   @override
   void dispose() {
     if (RawKeyboard.instance.keyEventHandler == _handleRawKeyEvent) {
       RawKeyboard.instance.keyEventHandler = null;
-      GestureBinding.instance!.pointerRouter.removeGlobalRoute(_handlePointerEvent);
+      GestureBinding.instance.pointerRouter.removeGlobalRoute(_handlePointerEvent);
     }
     super.dispose();
   }
 
   /// Provides convenient access to the current [FocusManager] singleton from
   /// the [WidgetsBinding] instance.
-  static FocusManager get instance => WidgetsBinding.instance!.focusManager;
+  static FocusManager get instance => WidgetsBinding.instance.focusManager;
 
   /// Sets the strategy by which [highlightMode] is determined.
   ///
@@ -1522,7 +1522,7 @@ class FocusManager with DiagnosticableTreeMixin, ChangeNotifier {
       case TargetPlatform.android:
       case TargetPlatform.fuchsia:
       case TargetPlatform.iOS:
-        if (WidgetsBinding.instance!.mouseTracker.mouseIsConnected) {
+        if (WidgetsBinding.instance.mouseTracker.mouseIsConnected) {
           return FocusHighlightMode.traditional;
         }
         return FocusHighlightMode.touch;
@@ -1821,7 +1821,7 @@ class FocusManager with DiagnosticableTreeMixin, ChangeNotifier {
 
 /// Provides convenient access to the current [FocusManager.primaryFocus] from the
 /// [WidgetsBinding] instance.
-FocusNode? get primaryFocus => WidgetsBinding.instance!.focusManager.primaryFocus;
+FocusNode? get primaryFocus => WidgetsBinding.instance.focusManager.primaryFocus;
 
 /// Returns a text representation of the current focus tree, along with the
 /// current attributes on each node.

packages/flutter/lib/src/widgets/framework.dart

@@ -149,7 +149,7 @@ abstract class GlobalKey<T extends State<StatefulWidget>> extends Key {
   /// constructor.
   const GlobalKey.constructor() : super.empty();
 
-  Element? get _currentElement => WidgetsBinding.instance!.buildOwner!._globalKeyRegistry[this];
+  Element? get _currentElement => WidgetsBinding.instance.buildOwner!._globalKeyRegistry[this];
 
   /// The build context in which the widget with this key builds.
   ///

packages/flutter/lib/src/widgets/heroes.dart

@@ -930,7 +930,7 @@ class HeroController extends NavigatorObserver {
         // going to end up, and the `to` route will go back onstage.
         to.offstage = to.animation!.value == 0.0;
 
-        WidgetsBinding.instance!.addPostFrameCallback((Duration value) {
+        WidgetsBinding.instance.addPostFrameCallback((Duration value) {
           _startHeroTransition(from, to, animation, flightType, isUserGestureTransition);
         });
       }

packages/flutter/lib/src/widgets/image.dart

@@ -119,7 +119,7 @@ Future<void> precacheImage(
       // Give callers until at least the end of the frame to subscribe to the
       // image stream.
       // See ImageCache._liveImages
-      SchedulerBinding.instance!.addPostFrameCallback((Duration timeStamp) {
+      SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) {
         stream.removeListener(listener!);
       });
     },
@@ -1118,14 +1118,14 @@ class _ImageState extends State<Image> with WidgetsBindingObserver {
   @override
   void initState() {
     super.initState();
-    WidgetsBinding.instance!.addObserver(this);
+    WidgetsBinding.instance.addObserver(this);
     _scrollAwareContext = DisposableBuildContext<State<Image>>(this);
   }
 
   @override
   void dispose() {
     assert(_imageStream != null);
-    WidgetsBinding.instance!.removeObserver(this);
+    WidgetsBinding.instance.removeObserver(this);
     _stopListeningToStream();
     _completerHandle?.dispose();
     _scrollAwareContext.dispose();
@@ -1175,7 +1175,7 @@ class _ImageState extends State<Image> with WidgetsBindingObserver {
 
   void _updateInvertColors() {
     _invertColors = MediaQuery.maybeOf(context)?.invertColors
-        ?? SemanticsBinding.instance!.accessibilityFeatures.invertColors;
+        ?? SemanticsBinding.instance.accessibilityFeatures.invertColors;
   }
 
   void _resolveImage() {

packages/flutter/lib/src/widgets/list_wheel_scroll_view.dart

@@ -759,7 +759,7 @@ class _ListWheelScrollViewState extends State<ListWheelScrollView> {
     super.didUpdateWidget(oldWidget);
     if (widget.controller != null && widget.controller != scrollController) {
       final ScrollController? oldScrollController = scrollController;
-      SchedulerBinding.instance!.addPostFrameCallback((_) {
+      SchedulerBinding.instance.addPostFrameCallback((_) {
         oldScrollController!.dispose();
       });
       scrollController = widget.controller;

packages/flutter/lib/src/widgets/localizations.dart

@@ -543,7 +543,7 @@ class _LocalizationsState extends State<Localizations> {
       // have finished loading. Until then the old locale will continue to be used.
       // - If we're running at app startup time then defer reporting the first
       // "useful" frame until after the async load has completed.
-      RendererBinding.instance!.deferFirstFrame();
+      RendererBinding.instance.deferFirstFrame();
       typeToResourcesFuture.then<void>((Map<Type, dynamic> value) {
         if (mounted) {
           setState(() {
@@ -551,7 +551,7 @@ class _LocalizationsState extends State<Localizations> {
             _locale = locale;
           });
         }
-        RendererBinding.instance!.allowFirstFrame();
+        RendererBinding.instance.allowFirstFrame();
       });
     }
   }

packages/flutter/lib/src/widgets/navigator.dart

@@ -3513,7 +3513,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
           // controller at the end of the build.
           if (newHeroController.navigator != null) {
             final NavigatorState previousOwner = newHeroController.navigator!;
-            ServicesBinding.instance!.addPostFrameCallback((Duration timestamp) {
+            ServicesBinding.instance.addPostFrameCallback((Duration timestamp) {
               // We only check if this navigator still owns the hero controller.
               if (_heroControllerFromScope == newHeroController) {
                 final bool hasHeroControllerOwnerShip = _heroControllerFromScope!._navigator == this;
@@ -5319,7 +5319,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
 
   void _cancelActivePointers() {
     // TODO(abarth): This mechanism is far from perfect. See https://github.com/flutter/flutter/issues/4770
-    if (SchedulerBinding.instance!.schedulerPhase == SchedulerPhase.idle) {
+    if (SchedulerBinding.instance.schedulerPhase == SchedulerPhase.idle) {
       // If we're between frames (SchedulerPhase.idle) then absorb any
       // subsequent pointers from this frame. The absorbing flag will be
       // reset in the next frame, see build().
@@ -5330,7 +5330,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
         // to false on the next frame.
       });
     }
-    _activePointers.toList().forEach(WidgetsBinding.instance!.cancelPointer);
+    _activePointers.toList().forEach(WidgetsBinding.instance.cancelPointer);
   }
 
   @override

packages/flutter/lib/src/widgets/nested_scroll_view.dart

@@ -1332,7 +1332,7 @@ class _NestedScrollController extends ScrollController {
     // the position change notifications because those happen synchronously
     // during a frame, at a time where it's too late to call setState. Since the
     // result is usually animated, the lag incurred is no big deal.
-    SchedulerBinding.instance!.addPostFrameCallback(
+    SchedulerBinding.instance.addPostFrameCallback(
       (Duration timeStamp) {
         coordinator.updateShadow();
       },

packages/flutter/lib/src/widgets/overlay.dart

@@ -151,8 +151,8 @@ class OverlayEntry extends ChangeNotifier {
       return;
 
     overlay._entries.remove(this);
-    if (SchedulerBinding.instance!.schedulerPhase == SchedulerPhase.persistentCallbacks) {
+    if (SchedulerBinding.instance.schedulerPhase == SchedulerPhase.persistentCallbacks) {
-      SchedulerBinding.instance!.addPostFrameCallback((Duration duration) {
+      SchedulerBinding.instance.addPostFrameCallback((Duration duration) {
         overlay._markDirty();
       });
     } else {

packages/flutter/lib/src/widgets/reorderable_list.dart

@@ -627,7 +627,7 @@ class SliverReorderableListState extends State<SliverReorderableList> with Ticke
     item.dragging = true;
     item.rebuild();
     _dragStartTransitionComplete = false;
-    SchedulerBinding.instance!.addPostFrameCallback((Duration duration) {
+    SchedulerBinding.instance.addPostFrameCallback((Duration duration) {
       _dragStartTransitionComplete = true;
     });
 

packages/flutter/lib/src/widgets/restoration.dart

@@ -275,18 +275,18 @@ class _RootRestorationScopeState extends State<RootRestorationScope> {
   void _loadRootBucketIfNecessary() {
     if (_isWaitingForRootBucket && !_isLoadingRootBucket) {
       _isLoadingRootBucket = true;
-      RendererBinding.instance!.deferFirstFrame();
+      RendererBinding.instance.deferFirstFrame();
-      ServicesBinding.instance!.restorationManager.rootBucket.then((RestorationBucket? bucket) {
+      ServicesBinding.instance.restorationManager.rootBucket.then((RestorationBucket? bucket) {
         _isLoadingRootBucket = false;
         if (mounted) {
-          ServicesBinding.instance!.restorationManager.addListener(_replaceRootBucket);
+          ServicesBinding.instance.restorationManager.addListener(_replaceRootBucket);
           setState(() {
             _rootBucket = bucket;
             _rootBucketValid = true;
             _okToRenderBlankContainer = false;
           });
         }
-        RendererBinding.instance!.allowFirstFrame();
+        RendererBinding.instance.allowFirstFrame();
       });
     }
   }
@@ -294,7 +294,7 @@ class _RootRestorationScopeState extends State<RootRestorationScope> {
   void _replaceRootBucket() {
     _rootBucketValid = false;
     _rootBucket = null;
-    ServicesBinding.instance!.restorationManager.removeListener(_replaceRootBucket);
+    ServicesBinding.instance.restorationManager.removeListener(_replaceRootBucket);
     _loadRootBucketIfNecessary();
     assert(!_isWaitingForRootBucket); // Ensure that load finished synchronously.
   }
@@ -302,7 +302,7 @@ class _RootRestorationScopeState extends State<RootRestorationScope> {
   @override
   void dispose() {
     if (_rootBucketValid) {
-      ServicesBinding.instance!.restorationManager.removeListener(_replaceRootBucket);
+      ServicesBinding.instance.restorationManager.removeListener(_replaceRootBucket);
     }
     super.dispose();
   }

packages/flutter/lib/src/widgets/router.dart

@@ -504,7 +504,7 @@ class _RouterState<T> extends State<Router<T>> with RestorationMixin {
       return;
     assert(_currentIntentionToReport != _IntentionToReportRouteInformation.none);
     _routeInformationReportingTaskScheduled = true;
-    SchedulerBinding.instance!.addPostFrameCallback(_reportRouteInformation);
+    SchedulerBinding.instance.addPostFrameCallback(_reportRouteInformation);
   }
 
   void _reportRouteInformation(Duration timestamp) {
@@ -962,7 +962,7 @@ class RootBackButtonDispatcher extends BackButtonDispatcher with WidgetsBindingO
   @override
   void addCallback(ValueGetter<Future<bool>> callback) {
     if (!hasCallbacks)
-      WidgetsBinding.instance!.addObserver(this);
+      WidgetsBinding.instance.addObserver(this);
     super.addCallback(callback);
   }
 
@@ -970,7 +970,7 @@ class RootBackButtonDispatcher extends BackButtonDispatcher with WidgetsBindingO
   void removeCallback(ValueGetter<Future<bool>> callback) {
     super.removeCallback(callback);
     if (!hasCallbacks)
-      WidgetsBinding.instance!.removeObserver(this);
+      WidgetsBinding.instance.removeObserver(this);
   }
 
   @override
@@ -1356,7 +1356,7 @@ class PlatformRouteInformationProvider extends RouteInformationProvider with Wid
   @override
   void addListener(VoidCallback listener) {
     if (!hasListeners)
-      WidgetsBinding.instance!.addObserver(this);
+      WidgetsBinding.instance.addObserver(this);
     super.addListener(listener);
   }
 
@@ -1364,7 +1364,7 @@ class PlatformRouteInformationProvider extends RouteInformationProvider with Wid
   void removeListener(VoidCallback listener) {
     super.removeListener(listener);
     if (!hasListeners)
-      WidgetsBinding.instance!.removeObserver(this);
+      WidgetsBinding.instance.removeObserver(this);
   }
 
   @override
@@ -1374,7 +1374,7 @@ class PlatformRouteInformationProvider extends RouteInformationProvider with Wid
     // is no longer being used, there's no listener, and so it will get garbage
     // collected.
     if (hasListeners)
-      WidgetsBinding.instance!.removeObserver(this);
+      WidgetsBinding.instance.removeObserver(this);
     super.dispose();
   }
 

packages/flutter/lib/src/widgets/routes.dart

@@ -616,11 +616,11 @@ mixin LocalHistoryRoute<T> on Route<T> {
     entry._owner = null;
     entry._notifyRemoved();
     if (_localHistory!.isEmpty) {
-      if (SchedulerBinding.instance!.schedulerPhase == SchedulerPhase.persistentCallbacks) {
+      if (SchedulerBinding.instance.schedulerPhase == SchedulerPhase.persistentCallbacks) {
         // The local history might be removed as a result of disposing inactive
         // elements during finalizeTree. The state is locked at this moment, and
         // we can only notify state has changed in the next frame.
-        SchedulerBinding.instance!.addPostFrameCallback((Duration duration) {
+        SchedulerBinding.instance.addPostFrameCallback((Duration duration) {
           changedInternalState();
         });
       } else {

packages/flutter/lib/src/widgets/scroll_aware_image_provider.dart

@@ -83,7 +83,7 @@ class ScrollAwareImageProvider<T extends Object> extends ImageProvider<T> {
     // Do this before checking scrolling, so that if the bytes are available we
     // render them even though we're scrolling fast - there's no additional
     // allocations to do for texture memory, it's already there.
-    if (stream.completer != null || PaintingBinding.instance!.imageCache!.containsKey(key)) {
+    if (stream.completer != null || PaintingBinding.instance.imageCache.containsKey(key)) {
       imageProvider.resolveStreamForKey(configuration, stream, key, handleError);
       return;
     }
@@ -96,7 +96,7 @@ class ScrollAwareImageProvider<T extends Object> extends ImageProvider<T> {
     // Try to get to end of the frame callbacks of the next frame, and then
     // check again.
     if (Scrollable.recommendDeferredLoadingForContext(context.context!)) {
-      SchedulerBinding.instance!.scheduleFrameCallback((_) {
+      SchedulerBinding.instance.scheduleFrameCallback((Duration timeStamp) {
         scheduleMicrotask(() => resolveStreamForKey(configuration, stream, key, handleError));
       });
       return;

packages/flutter/lib/src/widgets/scroll_physics.dart

@@ -224,7 +224,7 @@ class ScrollPhysics {
     assert(metrics != null);
     assert(context != null);
     if (parent == null) {
-      final double maxPhysicalPixels = WidgetsBinding.instance!.window.physicalSize.longestSide;
+      final double maxPhysicalPixels = WidgetsBinding.instance.window.physicalSize.longestSide;
       return velocity.abs() > maxPhysicalPixels;
     }
     return parent!.recommendDeferredLoading(velocity, metrics, context);
@@ -356,8 +356,8 @@ class ScrollPhysics {
   static final Tolerance _kDefaultTolerance = Tolerance(
     // TODO(ianh): Handle the case of the device pixel ratio changing.
     // TODO(ianh): Get this from the local MediaQuery not dart:ui's window object.
-    velocity: 1.0 / (0.050 * WidgetsBinding.instance!.window.devicePixelRatio), // logical pixels per second
+    velocity: 1.0 / (0.050 * WidgetsBinding.instance.window.devicePixelRatio), // logical pixels per second
-    distance: 1.0 / WidgetsBinding.instance!.window.devicePixelRatio, // logical pixels
+    distance: 1.0 / WidgetsBinding.instance.window.devicePixelRatio, // logical pixels
   );
 
   /// The tolerance to use for ballistic simulations.

packages/flutter/lib/src/widgets/scroll_position.dart

@@ -254,7 +254,7 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
   /// If there is any overscroll, it is reported using [didOverscrollBy].
   double setPixels(double newPixels) {
     assert(hasPixels);
-    assert(SchedulerBinding.instance!.schedulerPhase != SchedulerPhase.persistentCallbacks, "A scrollable's position should not change during the build, layout, and paint phases, otherwise the rendering will be confused.");
+    assert(SchedulerBinding.instance.schedulerPhase != SchedulerPhase.persistentCallbacks, "A scrollable's position should not change during the build, layout, and paint phases, otherwise the rendering will be confused.");
     if (newPixels != pixels) {
       final double overscroll = applyBoundaryConditions(newPixels);
       assert(() {
@@ -375,7 +375,7 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
     _impliedVelocity = value - pixels;
     _pixels = value;
     notifyListeners();
-    SchedulerBinding.instance!.addPostFrameCallback((Duration timeStamp) {
+    SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) {
       _impliedVelocity = 0;
     });
   }

packages/flutter/lib/src/widgets/scrollable.dart

@@ -440,7 +440,7 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin, R
     _persistedScrollOffset.value = offset;
     // [saveOffset] is called after a scrolling ends and it is usually not
     // followed by a frame. Therefore, manually flush restoration data.
-    ServicesBinding.instance!.restorationManager.flushData();
+    ServicesBinding.instance.restorationManager.flushData();
   }
 
   @override
@@ -705,7 +705,7 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin, R
       final double targetScrollOffset = _targetScrollOffsetForPointerScroll(delta);
       // Only express interest in the event if it would actually result in a scroll.
       if (delta != 0.0 && targetScrollOffset != position.pixels) {
-        GestureBinding.instance!.pointerSignalResolver.register(event, _handlePointerScroll);
+        GestureBinding.instance.pointerSignalResolver.register(event, _handlePointerScroll);
       }
     }
   }