Add maybeOf for all the cases where of returns nullable. (#114120)

dev/integration_tests/flutter_gallery/lib/demo/material/expansion_panels_demo.dart

@@ -210,8 +210,8 @@ class _ExpansionPanelsDemoState extends State<ExpansionPanelsDemo> {
               builder: (BuildContext context) {
                 return CollapsibleBody(
                   margin: const EdgeInsets.symmetric(horizontal: 16.0),
-                  onSave: () { Form.of(context)!.save(); close(); },
+                  onSave: () { Form.of(context).save(); close(); },
-                  onCancel: () { Form.of(context)!.reset(); close(); },
+                  onCancel: () { Form.of(context).reset(); close(); },
                   child: Padding(
                     padding: const EdgeInsets.symmetric(horizontal: 16.0),
                     child: TextFormField(
@@ -244,8 +244,8 @@ class _ExpansionPanelsDemoState extends State<ExpansionPanelsDemo> {
             child: Builder(
               builder: (BuildContext context) {
                 return CollapsibleBody(
-                  onSave: () { Form.of(context)!.save(); close(); },
+                  onSave: () { Form.of(context).save(); close(); },
-                  onCancel: () { Form.of(context)!.reset(); close(); },
+                  onCancel: () { Form.of(context).reset(); close(); },
                   child: FormField<Location>(
                     initialValue: item.value,
                     onSaved: (Location? result) { item.value = result; },
@@ -298,8 +298,8 @@ class _ExpansionPanelsDemoState extends State<ExpansionPanelsDemo> {
             child: Builder(
               builder: (BuildContext context) {
                 return CollapsibleBody(
-                  onSave: () { Form.of(context)!.save(); close(); },
+                  onSave: () { Form.of(context).save(); close(); },
-                  onCancel: () { Form.of(context)!.reset(); close(); },
+                  onCancel: () { Form.of(context).reset(); close(); },
                   child: FormField<double>(
                     initialValue: item.value,
                     onSaved: (double? value) { item.value = value; },

dev/integration_tests/flutter_gallery/lib/demo/material/page_selector_demo.dart

@@ -12,7 +12,7 @@ class _PageSelector extends StatelessWidget {
   final List<Icon>? icons;
 
   void _handleArrowButtonPress(BuildContext context, int delta) {
-    final TabController controller = DefaultTabController.of(context)!;
+    final TabController controller = DefaultTabController.of(context);
     if (!controller.indexIsChanging) {
       controller.animateTo((controller.index + delta).clamp(0, icons!.length - 1));
     }
@@ -20,7 +20,7 @@ class _PageSelector extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final TabController? controller = DefaultTabController.of(context);
+    final TabController? controller = DefaultTabController.maybeOf(context);
     final Color color = Theme.of(context).colorScheme.secondary;
     return SafeArea(
       top: false,

dev/integration_tests/flutter_gallery/lib/gallery/demo.dart

@@ -63,7 +63,7 @@ class TabbedComponentDemoScaffold extends StatefulWidget {
 
 class _TabbedComponentDemoScaffoldState extends State<TabbedComponentDemoScaffold> {
   void _showExampleCode(BuildContext context) {
-    final String? tag = widget.demos![DefaultTabController.of(context)!.index].exampleCodeTag;
+    final String? tag = widget.demos![DefaultTabController.of(context).index].exampleCodeTag;
     if (tag != null) {
       Navigator.push(context, MaterialPageRoute<FullScreenCodeDialog>(
         builder: (BuildContext context) => FullScreenCodeDialog(exampleCodeTag: tag)
@@ -72,7 +72,7 @@ class _TabbedComponentDemoScaffoldState extends State<TabbedComponentDemoScaffol
   }
 
   Future<void> _showApiDocumentation(BuildContext context) async {
-    final String? url = widget.demos![DefaultTabController.of(context)!.index].documentationUrl;
+    final String? url = widget.demos![DefaultTabController.of(context).index].documentationUrl;
     if (url == null) {
       return;
     }

dev/manual_tests/lib/material_arc.dart

@@ -451,7 +451,7 @@ class _AnimationDemoState extends State<AnimationDemo> with TickerProviderStateM
             return FloatingActionButton(
               child: const Icon(Icons.refresh),
               onPressed: () {
-                _play(_allDemos[DefaultTabController.of(context)!.index]);
+                _play(_allDemos[DefaultTabController.of(context).index]);
               },
             );
           },

dev/manual_tests/lib/overlay_geometry.dart

@@ -172,8 +172,8 @@ class OverlayGeometryAppState extends State<OverlayGeometryApp> {
       markers[MarkerType.topLeft] = box!.localToGlobal(Offset.zero);
       final Size size = box.size;
       markers[MarkerType.bottomRight] = box.localToGlobal(Offset(size.width, size.height));
-      final ScrollableState? scrollable = Scrollable.of(target.currentContext!);
+      final ScrollableState scrollable = Scrollable.of(target.currentContext!);
-      markersScrollOffset = scrollable!.position.pixels;
+      markersScrollOffset = scrollable.position.pixels;
     });
   }
 

examples/api/lib/cupertino/text_form_field_row/cupertino_text_form_field_row.1.dart

@@ -34,7 +34,7 @@ class FromSectionExample extends StatelessWidget {
         child: Form(
           autovalidateMode: AutovalidateMode.always,
           onChanged: () {
-            Form.of(primaryFocus!.context!)?.save();
+            Form.maybeOf(primaryFocus!.context!)?.save();
           },
           child: CupertinoFormSection.insetGrouped(
             header: const Text('SECTION 1'),

examples/api/lib/material/tab_controller/tab_controller.1.dart

@@ -38,7 +38,7 @@ class MyStatelessWidget extends StatelessWidget {
       // The Builder widget is used to have a different BuildContext to access
       // closest DefaultTabController.
       child: Builder(builder: (BuildContext context) {
-        final TabController tabController = DefaultTabController.of(context)!;
+        final TabController tabController = DefaultTabController.of(context);
         tabController.addListener(() {
           if (!tabController.indexIsChanging) {
             // Your code goes here.

examples/api/lib/material/text_form_field/text_form_field.1.dart

@@ -44,7 +44,7 @@ class _MyStatefulWidgetState extends State<MyStatefulWidget> {
             child: Form(
               autovalidateMode: AutovalidateMode.always,
               onChanged: () {
-                Form.of(primaryFocus!.context!)!.save();
+                Form.of(primaryFocus!.context!).save();
               },
               child: Wrap(
                 children: List<Widget>.generate(5, (int index) {

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

@@ -90,7 +90,7 @@ class CupertinoPageScaffold extends StatefulWidget {
 class _CupertinoPageScaffoldState extends State<CupertinoPageScaffold> {
 
   void _handleStatusBarTap() {
-    final ScrollController? primaryScrollController = PrimaryScrollController.of(context);
+    final ScrollController? primaryScrollController = PrimaryScrollController.maybeOf(context);
     // Only act on the scroll controller if it has any attached scroll positions.
     if (primaryScrollController != null && primaryScrollController.hasClients) {
       primaryScrollController.animateTo(

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

@@ -602,7 +602,7 @@ class _PackagesViewState extends State<_PackagesView> {
     }
     final String packageName = data.packages[widget.selectedId.value ?? 0];
     final List<int> bindings = data.packageLicenseBindings[packageName]!;
-    _MasterDetailFlow.of(context)!.setInitialDetailPage(
+    _MasterDetailFlow.of(context).setInitialDetailPage(
       _DetailArguments(
         packageName,
         bindings.map((int i) => data.licenses[i]).toList(growable: false),
@@ -632,7 +632,7 @@ class _PackagesViewState extends State<_PackagesView> {
           numberLicenses: bindings.length,
           onTap: () {
             widget.selectedId.value = packageIndex;
-            _MasterDetailFlow.of(context)!.openDetailPage(_DetailArguments(
+            _MasterDetailFlow.of(context).openDetailPage(_DetailArguments(
               packageName,
               bindings.map((int i) => data.licenses[i]).toList(growable: false),
             ));
@@ -1073,7 +1073,7 @@ class _MasterDetailFlow extends StatefulWidget {
   // ```dart
   // _MasterDetailFlow.of(context).openDetailPage(arguments);
   // ```
-  static _MasterDetailFlowProxy? of(BuildContext context) {
+  static _MasterDetailFlowProxy of(BuildContext context) {
     _PageOpener? pageOpener = context.findAncestorStateOfType<_MasterDetailScaffoldState>();
     pageOpener ??= context.findAncestorStateOfType<_MasterDetailFlowState>();
     assert(() {
@@ -1086,7 +1086,7 @@ class _MasterDetailFlow extends StatefulWidget {
       }
       return true;
     }());
-    return pageOpener != null ? _MasterDetailFlowProxy._(pageOpener) : null;
+    return _MasterDetailFlowProxy._(pageOpener!);
   }
 }
 
@@ -1339,13 +1339,13 @@ class _MasterDetailScaffoldState extends State<_MasterDetailScaffold>
   @override
   void openDetailPage(Object arguments) {
     SchedulerBinding.instance.addPostFrameCallback((_) => _detailArguments.value = arguments);
-    _MasterDetailFlow.of(context)!.openDetailPage(arguments);
+    _MasterDetailFlow.of(context).openDetailPage(arguments);
   }
 
   @override
   void setInitialDetailPage(Object arguments) {
     SchedulerBinding.instance.addPostFrameCallback((_) => _detailArguments.value = arguments);
-    _MasterDetailFlow.of(context)!.setInitialDetailPage(arguments);
+    _MasterDetailFlow.of(context).setInitialDetailPage(arguments);
   }
 
   @override

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

@@ -820,13 +820,9 @@ class _AppBarState extends State<AppBar> {
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
-    if (_scrollNotificationObserver != null) {
+    _scrollNotificationObserver?.removeListener(_handleScrollNotification);
-      _scrollNotificationObserver!.removeListener(_handleScrollNotification);
+    _scrollNotificationObserver = ScrollNotificationObserver.maybeOf(context);
-    }
+    _scrollNotificationObserver?.addListener(_handleScrollNotification);
-    _scrollNotificationObserver = ScrollNotificationObserver.of(context);
-    if (_scrollNotificationObserver != null) {
-      _scrollNotificationObserver!.addListener(_handleScrollNotification);
-    }
   }
 
   @override

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

@@ -806,7 +806,7 @@ class _FocusedDate extends InheritedWidget {
     return !DateUtils.isSameDay(date, oldWidget.date);
   }
 
-  static DateTime? of(BuildContext context) {
+  static DateTime? maybeOf(BuildContext context) {
     final _FocusedDate? focusedDate = context.dependOnInheritedWidgetOfExactType<_FocusedDate>();
     return focusedDate?.date;
   }
@@ -887,7 +887,7 @@ class _DayPickerState extends State<_DayPicker> {
   void didChangeDependencies() {
     super.didChangeDependencies();
     // Check to see if the focused date is in this month, if so focus it.
-    final DateTime? focusedDate = _FocusedDate.of(context);
+    final DateTime? focusedDate = _FocusedDate.maybeOf(context);
     if (focusedDate != null && DateUtils.isSameMonth(widget.displayedMonth, focusedDate)) {
       _dayFocusNodes[focusedDate.day - 1].requestFocus();
     }

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

@@ -1940,12 +1940,11 @@ class _FocusedDate extends InheritedWidget {
     return !DateUtils.isSameDay(date, oldWidget.date) || scrollDirection != oldWidget.scrollDirection;
   }
 
-  static _FocusedDate? of(BuildContext context) {
+  static _FocusedDate? maybeOf(BuildContext context) {
     return context.dependOnInheritedWidgetOfExactType<_FocusedDate>();
   }
 }
 
-
 class _DayHeaders extends StatelessWidget {
   const _DayHeaders();
 
@@ -2217,7 +2216,7 @@ class _MonthItemState extends State<_MonthItem> {
   void didChangeDependencies() {
     super.didChangeDependencies();
     // Check to see if the focused date is in this month, if so focus it.
-    final DateTime? focusedDate = _FocusedDate.of(context)?.date;
+    final DateTime? focusedDate = _FocusedDate.maybeOf(context)?.date;
     if (focusedDate != null && DateUtils.isSameMonth(widget.displayedMonth, focusedDate)) {
       _dayFocusNodes[focusedDate.day - 1].requestFocus();
     }
@@ -2237,7 +2236,7 @@ class _MonthItemState extends State<_MonthItem> {
 
   void _dayFocusChanged(bool focused) {
     if (focused) {
-      final TraversalDirection? focusDirection = _FocusedDate.of(context)?.scrollDirection;
+      final TraversalDirection? focusDirection = _FocusedDate.maybeOf(context)?.scrollDirection;
       if (focusDirection != null) {
         ScrollPositionAlignmentPolicy policy = ScrollPositionAlignmentPolicy.explicit;
         switch (focusDirection) {

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

@@ -332,7 +332,7 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
     _iconColor = _controller.drive(_iconColorTween.chain(_easeInTween));
     _backgroundColor = _controller.drive(_backgroundColorTween.chain(_easeOutTween));
 
-    _isExpanded = PageStorage.of(context)?.readState(context) as bool? ?? widget.initiallyExpanded;
+    _isExpanded = PageStorage.maybeOf(context)?.readState(context) as bool? ?? widget.initiallyExpanded;
     if (_isExpanded) {
       _controller.value = 1.0;
     }
@@ -359,7 +359,7 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
           });
         });
       }
-      PageStorage.of(context)?.writeState(context, _isExpanded);
+      PageStorage.maybeOf(context)?.writeState(context, _isExpanded);
     });
     widget.onExpansionChanged?.call(_isExpanded);
   }

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

@@ -284,7 +284,7 @@ class _InkState extends State<Ink> {
       _ink = InkDecoration(
         decoration: widget.decoration,
         configuration: createLocalImageConfiguration(context),
-        controller: Material.of(context)!,
+        controller: Material.of(context),
         referenceBox: _boxKey.currentContext!.findRenderObject()! as RenderBox,
         onRemoved: _handleRemoved,
       );

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

@@ -197,7 +197,7 @@ class _ParentInkResponseProvider extends InheritedWidget {
   @override
   bool updateShouldNotify(_ParentInkResponseProvider oldWidget) => state != oldWidget.state;
 
-  static _ParentInkResponseState? of(BuildContext context) {
+  static _ParentInkResponseState? maybeOf(BuildContext context) {
     return context.dependOnInheritedWidgetOfExactType<_ParentInkResponseProvider>()?.state;
   }
 }
@@ -600,7 +600,7 @@ class InkResponse extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final _ParentInkResponseState? parentState = _ParentInkResponseProvider.of(context);
+    final _ParentInkResponseState? parentState = _ParentInkResponseProvider.maybeOf(context);
     return _InkResponseStateWidget(
       onTap: onTap,
       onTapDown: onTapDown,
@@ -916,7 +916,7 @@ class _InkResponseState extends State<_InkResponseStateWidget>
         }
         final RenderBox referenceBox = context.findRenderObject()! as RenderBox;
         _highlights[type] = InkHighlight(
-          controller: Material.of(context)!,
+          controller: Material.of(context),
           referenceBox: referenceBox,
           color: resolvedOverlayColor,
           shape: widget.highlightShape,
@@ -952,7 +952,7 @@ class _InkResponseState extends State<_InkResponseStateWidget>
   }
 
   InteractiveInkFeature _createInkFeature(Offset globalPosition) {
-    final MaterialInkController inkController = Material.of(context)!;
+    final MaterialInkController inkController = Material.of(context);
     final RenderBox referenceBox = context.findRenderObject()! as RenderBox;
     final Offset position = referenceBox.globalToLocal(globalPosition);
     final Color color =  widget.overlayColor?.resolve(statesController.value) ?? widget.splashColor ?? Theme.of(context).splashColor;

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

@@ -348,14 +348,55 @@ class Material extends StatefulWidget {
   /// Typical usage is as follows:
   ///
   /// ```dart
-  /// MaterialInkController? inkController = Material.of(context);
+  /// MaterialInkController? inkController = Material.maybeOf(context);
   /// ```
   ///
   /// This method can be expensive (it walks the element tree).
-  static MaterialInkController? of(BuildContext context) {
+  ///
+  /// See also:
+  ///
+  /// * [Material.of], which is similar to this method, but asserts if
+  ///   no [Material] ancestor is found.
+  static MaterialInkController? maybeOf(BuildContext context) {
     return context.findAncestorRenderObjectOfType<_RenderInkFeatures>();
   }
 
+  /// The ink controller from the closest instance of [Material] that encloses
+  /// the given context.
+  ///
+  /// If no [Material] widget ancestor can be found then this method will assert
+  /// in debug mode, and throw an exception in release mode.
+  ///
+  /// Typical usage is as follows:
+  ///
+  /// ```dart
+  /// MaterialInkController inkController = Material.of(context);
+  /// ```
+  ///
+  /// This method can be expensive (it walks the element tree).
+  ///
+  /// See also:
+  ///
+  /// * [Material.maybeOf], which is similar to this method, but returns null if
+  ///   no [Material] ancestor is found.
+  static MaterialInkController of(BuildContext context) {
+    final MaterialInkController? controller = maybeOf(context);
+    assert(() {
+      if (controller == null) {
+        throw FlutterError(
+          'Material.of() was called with a context that does not contain a Material widget.\n'
+          'No Material widget ancestor could be found starting from the context that was passed to '
+          'Material.of(). This can happen because you are using a widget that looks for a Material '
+          'ancestor, but no such ancestor exists.\n'
+          'The context used was:\n'
+          '  $context',
+        );
+      }
+      return true;
+    }());
+    return controller!;
+  }
+
   @override
   State<Material> createState() => _MaterialState();
 

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

@@ -305,7 +305,7 @@ class _MenuAnchorState extends State<MenuAnchor> {
     _parent = _MenuAnchorState._maybeOf(context);
     _parent?._addChild(this);
     _position?.isScrollingNotifier.removeListener(_handleScroll);
-    _position = Scrollable.of(context)?.position;
+    _position = Scrollable.maybeOf(context)?.position;
     _position?.isScrollingNotifier.addListener(_handleScroll);
     final Size newSize = MediaQuery.of(context).size;
     if (_viewSize != null && newSize != _viewSize) {

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

@@ -267,7 +267,7 @@ class PaginatedDataTableState extends State<PaginatedDataTable> {
   @override
   void initState() {
     super.initState();
-    _firstRowIndex = PageStorage.of(context)?.readState(context) as int? ?? widget.initialFirstRowIndex ?? 0;
+    _firstRowIndex = PageStorage.maybeOf(context)?.readState(context) as int? ?? widget.initialFirstRowIndex ?? 0;
     widget.source.addListener(_handleDataSourceChanged);
     _handleDataSourceChanged();
   }

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

@@ -2536,7 +2536,7 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin, Resto
   // top. We implement this by looking up the primary scroll controller and
   // scrolling it to the top when tapped.
   void _handleStatusBarTap() {
-    final ScrollController? primaryScrollController = PrimaryScrollController.of(context);
+    final ScrollController? primaryScrollController = PrimaryScrollController.maybeOf(context);
     if (primaryScrollController != null && primaryScrollController.hasClients) {
       primaryScrollController.animateTo(
         0.0,

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

@@ -375,18 +375,65 @@ class DefaultTabController extends StatefulWidget {
   /// {@macro flutter.widgets.ProxyWidget.child}
   final Widget child;
 
-  /// The closest instance of this class that encloses the given context.
+  /// The closest instance of [DefaultTabController] that encloses the given
+  /// context, or null if none is found.
   ///
-  /// {@tool snippet}
+  /// {@tool snippet} Typical usage is as follows:
-  /// Typical usage is as follows:
   ///
   /// ```dart
-  /// TabController controller = DefaultTabController.of(context)!;
+  /// TabController? controller = DefaultTabController.maybeOf(context);
   /// ```
   /// {@end-tool}
-  static TabController? of(BuildContext context) {
+  ///
-    final _TabControllerScope? scope = context.dependOnInheritedWidgetOfExactType<_TabControllerScope>();
+  /// Calling this method will create a dependency on the closest
-    return scope?.controller;
+  /// [DefaultTabController] in the [context], if there is one.
+  ///
+  /// See also:
+  ///
+  /// * [DefaultTabController.of], which is similar to this method, but asserts
+  ///   if no [DefaultTabController] ancestor is found.
+  static TabController? maybeOf(BuildContext context) {
+    return context.dependOnInheritedWidgetOfExactType<_TabControllerScope>()?.controller;
+  }
+
+  /// The closest instance of [DefaultTabController] that encloses the given
+  /// context.
+  ///
+  /// If no instance is found, this method will assert in debug mode and throw
+  /// an exception in release mode.
+  ///
+  /// Calling this method will create a dependency on the closest
+  /// [DefaultTabController] in the [context].
+  ///
+  /// {@tool snippet} Typical usage is as follows:
+  ///
+  /// ```dart
+  /// TabController controller = DefaultTabController.of(context);
+  /// ```
+  /// {@end-tool}
+  ///
+  /// See also:
+  ///
+  /// * [DefaultTabController.maybeOf], which is similar to this method, but
+  ///   returns null if no [DefaultTabController] ancestor is found.
+  static TabController of(BuildContext context) {
+    final TabController? controller = maybeOf(context);
+    assert(() {
+      if (controller == null) {
+        throw FlutterError(
+          'DefaultTabController.of() was called with a context that does not '
+          'contain a DefaultTabController widget.\n'
+          'No DefaultTabController widget ancestor could be found starting from '
+          'the context that was passed to DefaultTabController.of(). This can '
+          'happen because you are using a widget that looks for a DefaultTabController '
+          'ancestor, but no such ancestor exists.\n'
+          'The context used was:\n'
+          '  $context',
+        );
+      }
+      return true;
+    }());
+    return controller!;
   }
 
   @override

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

@@ -954,7 +954,7 @@ class _TabBarState extends State<TabBar> {
     // TODO(xu-baolin): Remove automatic adjustment to white color indicator
     // with a better long-term solution.
     // https://github.com/flutter/flutter/pull/68171#pullrequestreview-517753917
-    if (widget.automaticIndicatorColorAdjustment && color.value == Material.of(context)?.color?.value) {
+    if (widget.automaticIndicatorColorAdjustment && color.value == Material.maybeOf(context)?.color?.value) {
       color = Colors.white;
     }
 
@@ -972,7 +972,7 @@ class _TabBarState extends State<TabBar> {
   bool get _controllerIsValid => _controller?.animation != null;
 
   void _updateTabController() {
-    final TabController? newController = widget.controller ?? DefaultTabController.of(context);
+    final TabController? newController = widget.controller ?? DefaultTabController.maybeOf(context);
     assert(() {
       if (newController == null) {
         throw FlutterError(
@@ -1411,7 +1411,7 @@ class _TabBarViewState extends State<TabBarView> {
   bool get _controllerIsValid => _controller?.animation != null;
 
   void _updateTabController() {
-    final TabController? newController = widget.controller ?? DefaultTabController.of(context);
+    final TabController? newController = widget.controller ?? DefaultTabController.maybeOf(context);
     assert(() {
       if (newController == null) {
         throw FlutterError(
@@ -1768,7 +1768,7 @@ class TabPageSelector extends StatelessWidget {
     final Color fixSelectedColor = selectedColor ?? Theme.of(context).colorScheme.secondary;
     final ColorTween selectedColorTween = ColorTween(begin: fixColor, end: fixSelectedColor);
     final ColorTween previousColorTween = ColorTween(begin: fixSelectedColor, end: fixColor);
-    final TabController? tabController = controller ?? DefaultTabController.of(context);
+    final TabController? tabController = controller ?? DefaultTabController.maybeOf(context);
 	  final MaterialLocalizations localizations = MaterialLocalizations.of(context);
     assert(() {
       if (tabController == null) {

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

@@ -38,7 +38,12 @@ abstract class RenderAbstractViewport extends RenderObject {
   ///
   /// If the object does not have a [RenderAbstractViewport] as an ancestor,
   /// this function returns null.
-  static RenderAbstractViewport? of(RenderObject? object) {
+  ///
+  /// See also:
+  ///
+  /// * [RenderAbstractViewport.of], which is similar to this method, but
+  ///   asserts if no [RenderAbstractViewport] ancestor is found.
+  static RenderAbstractViewport? maybeOf(RenderObject? object) {
     while (object != null) {
       if (object is RenderAbstractViewport) {
         return object;
@@ -48,6 +53,35 @@ abstract class RenderAbstractViewport extends RenderObject {
     return null;
   }
 
+  /// Returns the [RenderAbstractViewport] that most tightly encloses the given
+  /// render object.
+  ///
+  /// If the object does not have a [RenderAbstractViewport] as an ancestor,
+  /// this function will assert in debug mode, and throw an exception in release
+  /// mode.
+  ///
+  /// See also:
+  ///
+  /// * [RenderAbstractViewport.maybeOf], which is similar to this method, but
+  ///   returns null if no [RenderAbstractViewport] ancestor is found.
+  static RenderAbstractViewport of(RenderObject? object) {
+    final RenderAbstractViewport? viewport = maybeOf(object);
+    assert(() {
+      if (viewport == null) {
+        throw FlutterError(
+          'RenderAbstractViewport.of() was called with a render object that was '
+          'not a descendant of a RenderAbstractViewport.\n'
+          'No RenderAbstractViewport render object ancestor could be found starting '
+          'from the object that was passed to RenderAbstractViewport.of().\n'
+          'The render object where the viewport search started was:\n'
+          '  $object',
+        );
+      }
+      return true;
+    }());
+    return viewport!;
+  }
+
   /// Returns the offset that would be needed to reveal the `target`
   /// [RenderObject].
   ///

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

@@ -72,19 +72,62 @@ class AutofillGroup extends StatefulWidget {
     this.onDisposeAction = AutofillContextAction.commit,
   }) : assert(child != null);
 
-  /// Returns the closest [AutofillGroupState] which encloses the given context.
+  /// Returns the [AutofillGroupState] of the closest [AutofillGroup] widget
+  /// which encloses the given context, or null if one cannot be found.
+  ///
+  /// Calling this method will create a dependency on the closest
+  /// [AutofillGroup] in the [context], if there is one.
   ///
   /// {@macro flutter.widgets.AutofillGroupState}
   ///
   /// See also:
   ///
+  /// * [AutofillGroup.of], which is similar to this method, but asserts if an
+  ///   [AutofillGroup] cannot be found.
   /// * [EditableTextState], where this method is used to retrieve the closest
   ///   [AutofillGroupState].
-  static AutofillGroupState? of(BuildContext context) {
+  static AutofillGroupState? maybeOf(BuildContext context) {
     final _AutofillScope? scope = context.dependOnInheritedWidgetOfExactType<_AutofillScope>();
     return scope?._scope;
   }
 
+  /// Returns the [AutofillGroupState] of the closest [AutofillGroup] widget
+  /// which encloses the given context.
+  ///
+  /// If no instance is found, this method will assert in debug mode and throw
+  /// an exception in release mode.
+  ///
+  /// Calling this method will create a dependency on the closest
+  /// [AutofillGroup] in the [context].
+  ///
+  /// {@macro flutter.widgets.AutofillGroupState}
+  ///
+  /// See also:
+  ///
+  /// * [AutofillGroup.maybeOf], which is similar to this method, but returns
+  ///   null if an [AutofillGroup] cannot be found.
+  /// * [EditableTextState], where this method is used to retrieve the closest
+  ///   [AutofillGroupState].
+  static AutofillGroupState of(BuildContext context) {
+    final AutofillGroupState? groupState = maybeOf(context);
+    assert(() {
+      if (groupState == null) {
+        throw FlutterError(
+          'AutofillGroup.of() was called with a context that does not contain an '
+          'AutofillGroup widget.\n'
+          'No AutofillGroup widget ancestor could be found starting from the '
+          'context that was passed to AutofillGroup.of(). This can happen '
+          'because you are using a widget that looks for an AutofillGroup '
+          'ancestor, but no such ancestor exists.\n'
+          'The context used was:\n'
+          '  $context',
+        );
+      }
+      return true;
+    }());
+    return groupState!;
+  }
+
   /// {@macro flutter.widgets.ProxyWidget.child}
   final Widget child;
 
@@ -171,7 +214,7 @@ class AutofillGroupState extends State<AutofillGroup> with AutofillScopeMixin {
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
-    _isTopmostAutofillGroup = AutofillGroup.of(context) == null;
+    _isTopmostAutofillGroup = AutofillGroup.maybeOf(context) == null;
   }
 
   @override

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

@@ -2373,7 +2373,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
   void didChangeDependencies() {
     super.didChangeDependencies();
 
-    final AutofillGroupState? newAutofillGroup = AutofillGroup.of(context);
+    final AutofillGroupState? newAutofillGroup = AutofillGroup.maybeOf(context);
     if (currentAutofillScope != newAutofillGroup) {
       _currentAutofillScope?.unregister(autofillId);
       _currentAutofillScope = newAutofillGroup;
@@ -3481,7 +3481,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
       textAlign: widget.textAlign,
       textDirection: _textDirection,
       textScaleFactor: widget.textScaleFactor ?? MediaQuery.textScaleFactorOf(context),
-      textHeightBehavior: widget.textHeightBehavior ?? DefaultTextHeightBehavior.of(context),
+      textHeightBehavior: widget.textHeightBehavior ?? DefaultTextHeightBehavior.maybeOf(context),
       locale: widget.locale,
       structStyle: widget.strutStyle,
       placeholder: _placeholderLocation,
@@ -4150,7 +4150,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
                           textAlign: widget.textAlign,
                           textDirection: _textDirection,
                           locale: widget.locale,
-                          textHeightBehavior: widget.textHeightBehavior ?? DefaultTextHeightBehavior.of(context),
+                          textHeightBehavior: widget.textHeightBehavior ?? DefaultTextHeightBehavior.maybeOf(context),
                           textWidthBasis: widget.textWidthBasis,
                           obscuringCharacter: widget.obscuringCharacter,
                           obscureText: widget.obscureText,

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

@@ -623,7 +623,7 @@ mixin DirectionalFocusTraversalPolicyMixin on FocusTraversalPolicy {
       // Returns true if successfully popped the history.
       bool popOrInvalidate(TraversalDirection direction) {
         final FocusNode lastNode = policyData.history.removeLast().node;
-        if (Scrollable.of(lastNode.context!) != Scrollable.of(primaryFocus!.context!)) {
+        if (Scrollable.maybeOf(lastNode.context!) != Scrollable.maybeOf(primaryFocus!.context!)) {
           invalidateScopeData(nearestScope);
           return false;
         }
@@ -741,7 +741,7 @@ mixin DirectionalFocusTraversalPolicyMixin on FocusTraversalPolicy {
       return true;
     }
     FocusNode? found;
-    final ScrollableState? focusedScrollable = Scrollable.of(focusedChild.context!);
+    final ScrollableState? focusedScrollable = Scrollable.maybeOf(focusedChild.context!);
     switch (direction) {
       case TraversalDirection.down:
       case TraversalDirection.up:
@@ -751,7 +751,7 @@ mixin DirectionalFocusTraversalPolicyMixin on FocusTraversalPolicy {
           nearestScope.traversalDescendants,
         );
         if (focusedScrollable != null && !focusedScrollable.position.atEdge) {
-          final Iterable<FocusNode> filteredEligibleNodes = eligibleNodes!.where((FocusNode node) => Scrollable.of(node.context!) == focusedScrollable);
+          final Iterable<FocusNode> filteredEligibleNodes = eligibleNodes!.where((FocusNode node) => Scrollable.maybeOf(node.context!) == focusedScrollable);
           if (filteredEligibleNodes.isNotEmpty) {
             eligibleNodes = filteredEligibleNodes;
           }
@@ -783,7 +783,7 @@ mixin DirectionalFocusTraversalPolicyMixin on FocusTraversalPolicy {
       case TraversalDirection.left:
         Iterable<FocusNode>? eligibleNodes = _sortAndFilterHorizontally(direction, focusedChild.rect, nearestScope);
         if (focusedScrollable != null && !focusedScrollable.position.atEdge) {
-          final Iterable<FocusNode> filteredEligibleNodes = eligibleNodes!.where((FocusNode node) => Scrollable.of(node.context!) == focusedScrollable);
+          final Iterable<FocusNode> filteredEligibleNodes = eligibleNodes!.where((FocusNode node) => Scrollable.maybeOf(node.context!) == focusedScrollable);
           if (filteredEligibleNodes.isNotEmpty) {
             eligibleNodes = filteredEligibleNodes;
           }

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

@@ -49,20 +49,66 @@ class Form extends StatefulWidget {
   }) : assert(child != null),
        autovalidateMode = autovalidateMode ?? AutovalidateMode.disabled;
 
-  /// Returns the closest [FormState] which encloses the given context,
+  /// Returns the [FormState] of the closest [Form] widget which encloses the
-  /// or null if there is no such form.
+  /// given context, or null if none is found.
   ///
   /// Typical usage is as follows:
   ///
   /// ```dart
-  /// FormState form = Form.of(context)!;
+  /// FormState? form = Form.maybeOf(context);
-  /// form.save();
+  /// form?.save();
   /// ```
-  static FormState? of(BuildContext context) {
+  ///
+  /// Calling this method will create a dependency on the closest [Form] in the
+  /// [context], if there is one.
+  ///
+  /// See also:
+  ///
+  /// * [Form.of], which is similar to this method, but asserts if no [Form]
+  ///   ancestor is found.
+  static FormState? maybeOf(BuildContext context) {
     final _FormScope? scope = context.dependOnInheritedWidgetOfExactType<_FormScope>();
     return scope?._formState;
   }
 
+  /// Returns the [FormState] of the closest [Form] widget which encloses the
+  /// given context.
+  ///
+  /// Typical usage is as follows:
+  ///
+  /// ```dart
+  /// FormState form = Form.of(context);
+  /// form.save();
+  /// ```
+  ///
+  /// If no [Form] ancestor is found, this will assert in debug mode, and throw
+  /// an exception in release mode.
+  ///
+  /// Calling this method will create a dependency on the closest [Form] in the
+  /// [context].
+  ///
+  /// See also:
+  ///
+  /// * [Form.maybeOf], which is similar to this method, but returns null if no
+  ///   [Form] ancestor is found.
+  static FormState of(BuildContext context) {
+    final FormState? formState = maybeOf(context);
+    assert(() {
+      if (formState == null) {
+        throw FlutterError(
+          'Form.of() was called with a context that does not contain a Form widget.\n'
+          'No Form widget ancestor could be found starting from the context that '
+          'was passed to Form.of(). This can happen because you are using a widget '
+          'that looks for a Form ancestor, but no such ancestor exists.\n'
+          'The context used was:\n'
+          '  $context',
+        );
+      }
+      return true;
+    }());
+    return formState!;
+  }
+
   /// The widget below this widget in the tree.
   ///
   /// This is the root of the widget hierarchy that contains this form.
@@ -380,7 +426,7 @@ class FormFieldState<T> extends State<FormField<T>> with RestorationMixin {
       _hasInteractedByUser.value = false;
       _errorText.value = null;
     });
-    Form.of(context)?._fieldDidChange();
+    Form.maybeOf(context)?._fieldDidChange();
   }
 
   /// Calls [FormField.validator] to set the [errorText]. Returns true if there
@@ -414,7 +460,7 @@ class FormFieldState<T> extends State<FormField<T>> with RestorationMixin {
       _value = value;
       _hasInteractedByUser.value = true;
     });
-    Form.of(context)?._fieldDidChange();
+    Form.maybeOf(context)?._fieldDidChange();
   }
 
   /// Sets the value associated with this form field.
@@ -441,7 +487,7 @@ class FormFieldState<T> extends State<FormField<T>> with RestorationMixin {
 
   @override
   void deactivate() {
-    Form.of(context)?._unregister(this);
+    Form.maybeOf(context)?._unregister(this);
     super.deactivate();
   }
 
@@ -461,7 +507,7 @@ class FormFieldState<T> extends State<FormField<T>> with RestorationMixin {
           break;
       }
     }
-    Form.of(context)?._register(this);
+    Form.maybeOf(context)?._register(this);
     return widget.builder(this);
   }
 }

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

@@ -1605,8 +1605,12 @@ abstract class ParentDataWidget<T extends ParentData> extends ProxyWidget {
 ///
 ///   final Color color;
 ///
+///   static FrogColor? maybeOf(BuildContext context) {
+///     return context.dependOnInheritedWidgetOfExactType<FrogColor>();
+///   }
+///
 ///   static FrogColor of(BuildContext context) {
-///     final FrogColor? result = context.dependOnInheritedWidgetOfExactType<FrogColor>();
+///     final FrogColor? result = maybeOf(context);
 ///     assert(result != null, 'No FrogColor found in context');
 ///     return result!;
 ///   }
@@ -1617,30 +1621,35 @@ abstract class ParentDataWidget<T extends ParentData> extends ProxyWidget {
 /// ```
 /// {@end-tool}
 ///
-/// ## Implementing the `of` method
+/// ## Implementing the `of` and `maybeOf` methods
 ///
-/// The convention is to provide a static method `of` on the [InheritedWidget]
+/// The convention is to provide two static methods, `of` and `maybeOf`, on the
-/// which does the call to [BuildContext.dependOnInheritedWidgetOfExactType]. This
+/// [InheritedWidget] which call
-/// allows the class to define its own fallback logic in case there isn't
+/// [BuildContext.dependOnInheritedWidgetOfExactType]. This allows the class to
-/// a widget in scope. In the example above, the value returned will be
+/// define its own fallback logic in case there isn't a widget in scope.
-/// null in that case, but it could also have defaulted to a value.
 ///
-/// Sometimes, the `of` method returns the data rather than the inherited
+/// The `of` method typically returns a non-nullable instance and asserts if the
-/// widget; for example, in this case it could have returned a [Color] instead
+/// [InheritedWidget] isn't found, and the `maybeOf` method returns a nullable
-/// of the `FrogColor` widget.
+/// instance, and returns null if the [InheritedWidget] isn't found. The `of`
+/// method is typically implemented by calling `maybeOf` internally.
+///
+/// Sometimes, the `of` and `maybeOf` methods return some data rather than the
+/// inherited widget itself; for example, in this case it could have returned a
+/// [Color] instead of the `FrogColor` widget.
 ///
 /// Occasionally, the inherited widget is an implementation detail of another
-/// class, and is therefore private. The `of` method in that case is typically
+/// class, and is therefore private. The `of` and `maybeOf` methods in that case
-/// put on the public class instead. For example, [Theme] is implemented as a
+/// are typically implemented on the public class instead. For example, [Theme]
-/// [StatelessWidget] that builds a private inherited widget; [Theme.of] looks
+/// is implemented as a [StatelessWidget] that builds a private inherited
-/// for that inherited widget using [BuildContext.dependOnInheritedWidgetOfExactType]
+/// widget; [Theme.of] looks for that private inherited widget using
-/// and then returns the [ThemeData].
+/// [BuildContext.dependOnInheritedWidgetOfExactType] and then returns the
+/// [ThemeData] inside it.
 ///
-/// ## Calling the `of` method
+/// ## Calling the `of` or `maybeOf` methods
 ///
-/// When using the `of` method, the `context` must be a descendant of the
+/// When using the `of` or `maybeOf` methods, the `context` must be a descendant
-/// [InheritedWidget], meaning it must be "below" the [InheritedWidget] in the
+/// of the [InheritedWidget], meaning it must be "below" the [InheritedWidget]
-/// tree.
+/// in the tree.
 ///
 /// {@tool snippet}
 ///
@@ -1674,8 +1683,9 @@ abstract class ParentDataWidget<T extends ParentData> extends ProxyWidget {
 ///
 /// {@tool snippet}
 ///
-/// In this example, the `context` used is the one from the `MyOtherPage` widget,
+/// In this example, the `context` used is the one from the `MyOtherPage`
-/// which is a parent of the `FrogColor` widget, so this does not work.
+/// widget, which is a parent of the `FrogColor` widget, so this does not work,
+/// and will assert when `FrogColor.of` is called.
 ///
 /// ```dart
 /// // continuing from previous example...
@@ -1697,21 +1707,20 @@ abstract class ParentDataWidget<T extends ParentData> extends ProxyWidget {
 ///   }
 /// }
 /// ```
-/// {@end-tool}
+/// {@end-tool} {@youtube 560 315 https://www.youtube.com/watch?v=1t-8rBCGBYw}
-/// {@youtube 560 315 https://www.youtube.com/watch?v=1t-8rBCGBYw}
 ///
 /// See also:
 ///
-///  * [StatefulWidget] and [State], for widgets that can build differently
+/// * [StatefulWidget] and [State], for widgets that can build differently
-///    several times over their lifetime.
+///   several times over their lifetime.
-///  * [StatelessWidget], for widgets that always build the same way given a
+/// * [StatelessWidget], for widgets that always build the same way given a
-///    particular configuration and ambient state.
+///   particular configuration and ambient state.
-///  * [Widget], for an overview of widgets in general.
+/// * [Widget], for an overview of widgets in general.
-///  * [InheritedNotifier], an inherited widget whose value can be a
+/// * [InheritedNotifier], an inherited widget whose value can be a
-///    [Listenable], and which will notify dependents whenever the value
+///   [Listenable], and which will notify dependents whenever the value sends
-///    sends notifications.
+///   notifications.
-///  * [InheritedModel], an inherited widget that allows clients to subscribe
+/// * [InheritedModel], an inherited widget that allows clients to subscribe to
-///    to changes for subparts of the value.
+///   changes for subparts of the value.
 abstract class InheritedWidget extends ProxyWidget {
   /// Abstract const constructor. This constructor enables subclasses to provide
   /// const constructors so that they can be used in const expressions.

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

@@ -6,53 +6,61 @@ import 'dart:collection';
 
 import 'framework.dart';
 
-/// An [InheritedWidget] that's intended to be used as the base class for
+/// An [InheritedWidget] that's intended to be used as the base class for models
-/// models whose dependents may only depend on one part or "aspect" of the
+/// whose dependents may only depend on one part or "aspect" of the overall
-/// overall model.
+/// model.
 ///
 /// An inherited widget's dependents are unconditionally rebuilt when the
-/// inherited widget changes per [InheritedWidget.updateShouldNotify].
+/// inherited widget changes per [InheritedWidget.updateShouldNotify]. This
-/// This widget is similar except that dependents aren't rebuilt
+/// widget is similar except that dependents aren't rebuilt unconditionally.
-/// unconditionally.
 ///
-/// Widgets that depend on an [InheritedModel] qualify their dependence
+/// Widgets that depend on an [InheritedModel] qualify their dependence with a
-/// with a value that indicates what "aspect" of the model they depend
+/// value that indicates what "aspect" of the model they depend on. When the
-/// on. When the model is rebuilt, dependents will also be rebuilt, but
+/// model is rebuilt, dependents will also be rebuilt, but only if there was a
-/// only if there was a change in the model that corresponds to the aspect
+/// change in the model that corresponds to the aspect they provided.
-/// they provided.
 ///
 /// The type parameter `T` is the type of the model aspect objects.
 ///
 /// {@youtube 560 315 https://www.youtube.com/watch?v=ml5uefGgkaA}
 ///
 /// Widgets create a dependency on an [InheritedModel] with a static method:
-/// [InheritedModel.inheritFrom]. This method's `context` parameter
+/// [InheritedModel.inheritFrom]. This method's `context` parameter defines the
-/// defines the subtree that will be rebuilt when the model changes.
+/// subtree that will be rebuilt when the model changes. Typically the
-/// Typically the `inheritFrom` method is called from a model-specific
+/// `inheritFrom` method is called from a model-specific static `maybeOf` or
-/// static `of` method. For example:
+/// `of` methods, a convention that is present in many Flutter framework classes
+/// which look things up. For example:
 ///
 /// ```dart
 /// class MyModel extends InheritedModel<String> {
 ///   const MyModel({super.key, required super.child});
+///
 ///   // ...
-///   static MyModel? of(BuildContext context, String aspect) {
+///   static MyModel? maybeOf(BuildContext context, [String? aspect]) {
 ///     return InheritedModel.inheritFrom<MyModel>(context, aspect: aspect);
 ///   }
+///
+///   // ...
+///   static MyModel of(BuildContext context, [String? aspect]) {
+///     final MyModel? result = maybeOf(context, aspect);
+///     assert(result != null, 'Unable to find an instance of MyModel...');
+///     return result!;
+///   }
 /// }
 /// ```
 ///
-/// Calling `MyModel.of(context, 'foo')` means that `context` should only
+/// Calling `MyModel.of(context, 'foo')` or `MyModel.maybeOf(context,
-/// be rebuilt when the `foo` aspect of `MyModel` changes. If the aspect
+/// 'foo')` means that `context` should only be rebuilt when the `foo` aspect of
-/// is null, then the model supports all aspects.
+/// `MyModel` changes. If the `aspect` is null, then the model supports all
+/// aspects.
 ///
 /// {@tool snippet}
 /// When the inherited model is rebuilt the [updateShouldNotify] and
-/// [updateShouldNotifyDependent] methods are used to decide what
+/// [updateShouldNotifyDependent] methods are used to decide what should be
-/// should be rebuilt. If [updateShouldNotify] returns true, then the
+/// rebuilt. If [updateShouldNotify] returns true, then the inherited model's
-/// inherited model's [updateShouldNotifyDependent] method is tested for
+/// [updateShouldNotifyDependent] method is tested for each dependent and the
-/// each dependent and the set of aspect objects it depends on.
+/// set of aspect objects it depends on. The [updateShouldNotifyDependent]
-/// The [updateShouldNotifyDependent] method must compare the set of aspect
+/// method must compare the set of aspect dependencies with the changes in the
-/// dependencies with the changes in the model itself. For example:
+/// model itself. For example:
 ///
 /// ```dart
 /// class ABModel extends InheritedModel<String> {
@@ -85,26 +93,26 @@ import 'framework.dart';
 /// In the previous example the dependencies checked by
 /// [updateShouldNotifyDependent] are just the aspect strings passed to
 /// `dependOnInheritedWidgetOfExactType`. They're represented as a [Set] because
-/// one Widget can depend on more than one aspect of the model.
+/// one Widget can depend on more than one aspect of the model. If a widget
-/// If a widget depends on the model but doesn't specify an aspect,
+/// depends on the model but doesn't specify an aspect, then changes in the
-/// then changes in the model will cause the widget to be rebuilt
+/// model will cause the widget to be rebuilt unconditionally.
-/// unconditionally.
 ///
 /// {@tool dartpad}
-/// This example shows how to implement [InheritedModel] to rebuild a
+/// This example shows how to implement [InheritedModel] to rebuild a widget
-/// widget based on a qualified dependence. When tapped on the "Resize Logo" button
+/// based on a qualified dependence. When tapped on the "Resize Logo" button
-/// only the logo widget is rebuilt while the background widget remains unaffected.
+/// only the logo widget is rebuilt while the background widget remains
+/// unaffected.
 ///
 /// ** See code in examples/api/lib/widgets/inherited_model/inherited_model.0.dart **
 /// {@end-tool}
 ///
 /// See also:
 ///
-///  * [InheritedWidget], an inherited widget that only notifies dependents
+/// * [InheritedWidget], an inherited widget that only notifies dependents when
-///    when its value is different.
+///   its value is different.
-///  * [InheritedNotifier], an inherited widget whose value can be a
+/// * [InheritedNotifier], an inherited widget whose value can be a
-///    [Listenable], and which will notify dependents whenever the value
+///   [Listenable], and which will notify dependents whenever the value sends
-///    sends notifications.
+///   notifications.
 abstract class InheritedModel<T> extends InheritedWidget {
   /// Creates an inherited widget that supports dependencies qualified by
   /// "aspects", i.e. a descendant widget can indicate that it should

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

@@ -689,12 +689,53 @@ class HeroControllerScope extends InheritedWidget {
   final HeroController? controller;
 
   /// Retrieves the [HeroController] from the closest [HeroControllerScope]
-  /// ancestor.
+  /// ancestor, or null if none exists.
-  static HeroController? of(BuildContext context) {
+  ///
+  /// Calling this method will create a dependency on the closest
+  /// [HeroControllerScope] in the [context], if there is one.
+  ///
+  /// See also:
+  ///
+  /// * [HeroControllerScope.of], which is similar to this method, but asserts
+  ///   if no [HeroControllerScope] ancestor is found.
+  static HeroController? maybeOf(BuildContext context) {
     final HeroControllerScope? host = context.dependOnInheritedWidgetOfExactType<HeroControllerScope>();
     return host?.controller;
   }
 
+  /// Retrieves the [HeroController] from the closest [HeroControllerScope]
+  /// ancestor.
+  ///
+  /// If no ancestor is found, this method will assert in debug mode, and throw
+  /// an exception in release mode.
+  ///
+  /// Calling this method will create a dependency on the closest
+  /// [HeroControllerScope] in the [context].
+  ///
+  /// See also:
+  ///
+  /// * [HeroControllerScope.maybeOf], which is similar to this method, but
+  ///   returns null if no [HeroControllerScope] ancestor is found.
+  static HeroController of(BuildContext context) {
+    final HeroController? controller = maybeOf(context);
+    assert(() {
+      if (controller == null) {
+        throw FlutterError(
+          'HeroControllerScope.of() was called with a context that does not contain a '
+          'HeroControllerScope widget.\n'
+          'No HeroControllerScope widget ancestor could be found starting from the '
+          'context that was passed to HeroControllerScope.of(). This can happen '
+          'because you are using a widget that looks for a HeroControllerScope '
+          'ancestor, but no such ancestor exists.\n'
+          'The context used was:\n'
+          '  $context',
+        );
+      }
+      return true;
+    }());
+    return controller!;
+  }
+
   @override
   bool updateShouldNotify(HeroControllerScope oldWidget) {
     return oldWidget.controller != controller;
@@ -3350,7 +3391,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
-    _updateHeroController(HeroControllerScope.of(context));
+    _updateHeroController(HeroControllerScope.maybeOf(context));
     for (final _RouteEntry entry in _history) {
       entry.route.changedExternalState();
     }

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

@@ -1088,7 +1088,7 @@ class _NestedScrollCoordinator implements ScrollActivityDelegate, ScrollHoldCont
 
   void updateParent() {
     _outerPosition?.setParent(
-      _parent ?? PrimaryScrollController.of(_state.context),
+      _parent ?? PrimaryScrollController.maybeOf(_state.context),
     );
   }
 

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

@@ -174,22 +174,66 @@ class PageStorage extends StatelessWidget {
   /// The page storage bucket to use for this subtree.
   final PageStorageBucket bucket;
 
-  /// The bucket from the closest instance of this class that encloses the given context.
+  /// The [PageStorageBucket] from the closest instance of a [PageStorage]
+  /// widget that encloses the given context.
   ///
   /// Returns null if none exists.
   ///
   /// Typical usage is as follows:
   ///
   /// ```dart
-  /// PageStorageBucket bucket = PageStorage.of(context)!;
+  /// PageStorageBucket? bucket = PageStorage.of(context);
   /// ```
   ///
   /// This method can be expensive (it walks the element tree).
-  static PageStorageBucket? of(BuildContext context) {
+  ///
+  /// See also:
+  ///
+  /// * [PageStorage.of], which is similar to this method, but
+  ///   asserts if no [PageStorage] ancestor is found.
+  static PageStorageBucket? maybeOf(BuildContext context) {
     final PageStorage? widget = context.findAncestorWidgetOfExactType<PageStorage>();
     return widget?.bucket;
   }
 
+  /// The [PageStorageBucket] from the closest instance of a [PageStorage]
+  /// widget that encloses the given context.
+  ///
+  /// If no ancestor is found, this method will assert in debug mode, and throw
+  /// an exception in release mode.
+  ///
+  /// Typical usage is as follows:
+  ///
+  /// ```dart
+  /// PageStorageBucket bucket = PageStorage.of(context);
+  /// ```
+  ///
+  /// This method can be expensive (it walks the element tree).
+  ///
+  /// See also:
+  ///
+  /// * [PageStorage.maybeOf], which is similar to this method, but
+  ///   returns null if no [PageStorage] ancestor is found.
+  static PageStorageBucket of(BuildContext context) {
+    final PageStorageBucket? bucket = maybeOf(context);
+    assert(() {
+      if (bucket == null) {
+        throw FlutterError(
+          'PageStorage.of() was called with a context that does not contain a '
+          'PageStorage widget.\n'
+          'No PageStorage widget ancestor could be found starting from the '
+          'context that was passed to PageStorage.of(). This can happen '
+          'because you are using a widget that looks for a PageStorage '
+          'ancestor, but no such ancestor exists.\n'
+          'The context used was:\n'
+          '  $context',
+        );
+      }
+      return true;
+    }());
+    return bucket!;
+  }
+
   @override
   Widget build(BuildContext context) => child;
 }

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

@@ -403,13 +403,13 @@ class _PagePosition extends ScrollPositionWithSingleContext implements PageMetri
 
   @override
   void saveScrollOffset() {
-    PageStorage.of(context.storageContext)?.writeState(context.storageContext, _cachedPage ?? getPageFromPixels(pixels, viewportDimension));
+    PageStorage.maybeOf(context.storageContext)?.writeState(context.storageContext, _cachedPage ?? getPageFromPixels(pixels, viewportDimension));
   }
 
   @override
   void restoreScrollOffset() {
     if (!hasPixels) {
-      final double? value = PageStorage.of(context.storageContext)?.readState(context.storageContext) as double?;
+      final double? value = PageStorage.maybeOf(context.storageContext)?.readState(context.storageContext) as double?;
       if (value != null) {
         _pageToUseOnStartup = value;
       }

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

@@ -125,11 +125,52 @@ class PrimaryScrollController extends InheritedWidget {
   ///
   /// Returns null if there is no [ScrollController] associated with the given
   /// context.
-  static ScrollController? of(BuildContext context) {
+  ///
+  /// Calling this method will create a dependency on the closest
+  /// [PrimaryScrollController] in the [context], if there is one.
+  ///
+  /// See also:
+  ///
+  /// * [PrimaryScrollController.maybeOf], which is similar to this method, but
+  ///   asserts if no [PrimaryScrollController] ancestor is found.
+  static ScrollController? maybeOf(BuildContext context) {
     final PrimaryScrollController? result = context.dependOnInheritedWidgetOfExactType<PrimaryScrollController>();
     return result?.controller;
   }
 
+  /// Returns the [ScrollController] most closely associated with the given
+  /// context.
+  ///
+  /// If no ancestor is found, this method will assert in debug mode, and throw
+  /// an exception in release mode.
+  ///
+  /// Calling this method will create a dependency on the closest
+  /// [PrimaryScrollController] in the [context].
+  ///
+  /// See also:
+  ///
+  /// * [PrimaryScrollController.maybeOf], which is similar to this method, but
+  ///   returns null if no [PrimaryScrollController] ancestor is found.
+  static ScrollController of(BuildContext context) {
+    final ScrollController? controller = maybeOf(context);
+    assert(() {
+      if (controller == null) {
+        throw FlutterError(
+          'PrimaryScrollController.of() was called with a context that does not contain a '
+          'PrimaryScrollController widget.\n'
+          'No PrimaryScrollController widget ancestor could be found starting from the '
+          'context that was passed to PrimaryScrollController.of(). This can happen '
+          'because you are using a widget that looks for a PrimaryScrollController '
+          'ancestor, but no such ancestor exists.\n'
+          'The context used was:\n'
+          '  $context',
+        );
+      }
+      return true;
+    }());
+    return controller!;
+  }
+
   @override
   bool updateShouldNotify(PrimaryScrollController oldWidget) => controller != oldWidget.controller;
 

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

@@ -609,7 +609,7 @@ class SliverReorderableListState extends State<SliverReorderableList> with Ticke
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
-    _scrollable = Scrollable.of(context)!;
+    _scrollable = Scrollable.of(context);
     if (_autoScroller?.scrollable != _scrollable) {
       _autoScroller?.stopAutoScroll();
       _autoScroller = EdgeDraggingAutoScroller(

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

@@ -65,18 +65,63 @@ class RestorationScope extends StatefulWidget {
   /// Returns the [RestorationBucket] inserted into the widget tree by the
   /// closest ancestor [RestorationScope] of `context`.
   ///
+  /// {@template flutter.widgets.restoration.RestorationScope.bucket_warning}
   /// To avoid accidentally overwriting data already stored in the bucket by its
   /// owner, data should not be stored directly in the bucket returned by this
   /// method. Instead, consider claiming a child bucket from the returned bucket
   /// (via [RestorationBucket.claimChild]) and store the restoration data in
   /// that child.
+  /// {@endtemplate}
   ///
   /// This method returns null if state restoration is turned off for this
   /// subtree.
-  static RestorationBucket? of(BuildContext context) {
+  ///
+  /// Calling this method will create a dependency on the closest
+  /// [RestorationScope] in the [context], if there is one.
+  ///
+  /// See also:
+  ///
+  /// * [RestorationScope.maybeOf], which is similar to this method, but asserts
+  ///   if no [RestorationScope] ancestor is found.
+  static RestorationBucket? maybeOf(BuildContext context) {
     return context.dependOnInheritedWidgetOfExactType<UnmanagedRestorationScope>()?.bucket;
   }
 
+  /// Returns the [RestorationBucket] inserted into the widget tree by the
+  /// closest ancestor [RestorationScope] of `context`.
+  ///
+  /// {@macro flutter.widgets.restoration.RestorationScope.bucket_warning}
+  ///
+  /// This method will assert in debug mode and throw an exception in release
+  /// mode if state restoration is turned off for this subtree.
+  ///
+  /// Calling this method will create a dependency on the closest
+  /// [RestorationScope] in the [context].
+  ///
+  /// See also:
+  ///
+  /// * [RestorationScope.maybeOf], which is similar to this method, but returns
+  ///   null if no [RestorationScope] ancestor is found.
+  static RestorationBucket of(BuildContext context) {
+    final RestorationBucket? bucket = maybeOf(context);
+    assert(() {
+      if (bucket == null) {
+        throw FlutterError(
+          'RestorationScope.of() was called with a context that does not contain a '
+          'RestorationScope widget.\n'
+          'No RestorationScope widget ancestor could be found starting from the '
+          'context that was passed to RestorationScope.of(). This can happen '
+          'because you are using a widget that looks for a RestorationScope '
+          'ancestor, but no such ancestor exists.\n'
+          'The context used was:\n'
+          '  $context',
+        );
+      }
+      return true;
+    }());
+    return bucket!;
+  }
+
   /// The widget below this widget in the tree.
   ///
   /// {@macro flutter.widgets.ProxyWidget.child}
@@ -250,7 +295,7 @@ class _RootRestorationScopeState extends State<RootRestorationScope> {
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
-    _ancestorBucket = RestorationScope.of(context);
+    _ancestorBucket = RestorationScope.maybeOf(context);
     _loadRootBucketIfNecessary();
     _okToRenderBlankContainer ??= widget.restorationId != null && _needsRootBucketInserted;
   }
@@ -834,7 +879,7 @@ mixin RestorationMixin<S extends StatefulWidget> on State<S> {
     if (restorationId == null) {
       return false;
     }
-    final RestorationBucket? potentialNewParent = RestorationScope.of(context);
+    final RestorationBucket? potentialNewParent = RestorationScope.maybeOf(context);
     return potentialNewParent != _currentParent && (potentialNewParent?.isReplacing ?? false);
   }
 
@@ -850,7 +895,7 @@ mixin RestorationMixin<S extends StatefulWidget> on State<S> {
 
     final RestorationBucket? oldBucket = _bucket;
     final bool needsRestore = restorePending;
-    _currentParent = RestorationScope.of(context);
+    _currentParent = RestorationScope.maybeOf(context);
 
     final bool didReplaceBucket = _updateBucketIfNecessary(parent: _currentParent, restorePending: needsRestore);
 

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

@@ -45,13 +45,13 @@ class _ListenerEntry extends LinkedListEntry<_ListenerEntry> {
 /// To add a listener to a [ScrollNotificationObserver] ancestor:
 ///
 /// ```dart
-/// ScrollNotificationObserver.of(context)!.addListener(_listener);
+/// ScrollNotificationObserver.of(context).addListener(_listener);
 /// ```
 ///
 /// To remove the listener from a [ScrollNotificationObserver] ancestor:
 ///
 /// ```dart
-/// ScrollNotificationObserver.of(context)!.removeListener(_listener);
+/// ScrollNotificationObserver.of(context).removeListener(_listener);
 /// ```
 ///
 /// Stateful widgets that share an ancestor [ScrollNotificationObserver] typically
@@ -85,11 +85,52 @@ class ScrollNotificationObserver extends StatefulWidget {
 
   /// The closest instance of this class that encloses the given context.
   ///
-  /// If there is no enclosing [ScrollNotificationObserver] widget, then null is returned.
+  /// If there is no enclosing [ScrollNotificationObserver] widget, then null is
-  static ScrollNotificationObserverState? of(BuildContext context) {
+  /// returned.
+  ///
+  /// Calling this method will create a dependency on the closest
+  /// [ScrollNotificationObserver] in the [context], if there is one.
+  ///
+  /// See also:
+  ///
+  /// * [ScrollNotificationObserver.of], which is similar to this method, but
+  ///   asserts if no [ScrollNotificationObserver] ancestor is found.
+  static ScrollNotificationObserverState? maybeOf(BuildContext context) {
     return context.dependOnInheritedWidgetOfExactType<_ScrollNotificationObserverScope>()?._scrollNotificationObserverState;
   }
 
+  /// The closest instance of this class that encloses the given context.
+  ///
+  /// If no ancestor is found, this method will assert in debug mode, and throw
+  /// an exception in release mode.
+  ///
+  /// Calling this method will create a dependency on the closest
+  /// [ScrollNotificationObserver] in the [context].
+  ///
+  /// See also:
+  ///
+  /// * [ScrollNotificationObserver.maybeOf], which is similar to this method,
+  ///   but returns null if no [ScrollNotificationObserver] ancestor is found.
+  static ScrollNotificationObserverState of(BuildContext context) {
+    final ScrollNotificationObserverState? observerState = maybeOf(context);
+    assert(() {
+      if (observerState == null) {
+        throw FlutterError(
+          'ScrollNotificationObserver.of() was called with a context that does not contain a '
+          'ScrollNotificationObserver widget.\n'
+          'No ScrollNotificationObserver widget ancestor could be found starting from the '
+          'context that was passed to ScrollNotificationObserver.of(). This can happen '
+          'because you are using a widget that looks for a ScrollNotificationObserver '
+          'ancestor, but no such ancestor exists.\n'
+          'The context used was:\n'
+          '  $context',
+        );
+      }
+      return true;
+    }());
+    return observerState!;
+  }
+
   @override
   ScrollNotificationObserverState createState() => ScrollNotificationObserverState();
 }

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

@@ -402,7 +402,7 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
   // TODO(goderbauer): Deprecate this when state restoration supports all features of PageStorage.
   @protected
   void saveScrollOffset() {
-    PageStorage.of(context.storageContext)?.writeState(context.storageContext, pixels);
+    PageStorage.maybeOf(context.storageContext)?.writeState(context.storageContext, pixels);
   }
 
   /// Called whenever the [ScrollPosition] is created, to restore the scroll
@@ -424,7 +424,7 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
   @protected
   void restoreScrollOffset() {
     if (!hasPixels) {
-      final double? value = PageStorage.of(context.storageContext)?.readState(context.storageContext) as double?;
+      final double? value = PageStorage.maybeOf(context.storageContext)?.readState(context.storageContext) as double?;
       if (value != null) {
         correctPixels(value);
       }
@@ -703,7 +703,7 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
   }) {
     assert(alignmentPolicy != null);
     assert(object.attached);
-    final RenderAbstractViewport viewport = RenderAbstractViewport.of(object)!;
+    final RenderAbstractViewport viewport = RenderAbstractViewport.of(object);
     assert(viewport != null);
 
     Rect? targetRect;

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

@@ -411,7 +411,7 @@ abstract class ScrollView extends StatelessWidget {
         ?? controller == null && PrimaryScrollController.shouldInherit(context, scrollDirection);
 
     final ScrollController? scrollController = effectivePrimary
-        ? PrimaryScrollController.of(context)
+        ? PrimaryScrollController.maybeOf(context)
         : controller;
 
     final Scrollable scrollable = Scrollable(

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

@@ -289,21 +289,66 @@ class Scrollable extends StatefulWidget {
     properties.add(StringProperty('restorationId', restorationId));
   }
 
-  /// The state from the closest instance of this class that encloses the given context.
+  /// The state from the closest instance of this class that encloses the given
+  /// context, or null if none is found.
   ///
   /// Typical usage is as follows:
   ///
   /// ```dart
-  /// ScrollableState scrollable = Scrollable.of(context)!;
+  /// ScrollableState? scrollable = Scrollable.maybeOf(context);
   /// ```
   ///
   /// Calling this method will create a dependency on the closest [Scrollable]
   /// in the [context], if there is one.
-  static ScrollableState? of(BuildContext context) {
+  ///
+  /// See also:
+  ///
+  /// * [Scrollable.of], which is similar to this method, but asserts
+  ///   if no [Scrollable] ancestor is found.
+  static ScrollableState? maybeOf(BuildContext context) {
     final _ScrollableScope? widget = context.dependOnInheritedWidgetOfExactType<_ScrollableScope>();
     return widget?.scrollable;
   }
 
+  /// The state from the closest instance of this class that encloses the given
+  /// context.
+  ///
+  /// Typical usage is as follows:
+  ///
+  /// ```dart
+  /// ScrollableState scrollable = Scrollable.of(context);
+  /// ```
+  ///
+  /// Calling this method will create a dependency on the closest [Scrollable]
+  /// in the [context].
+  ///
+  /// If no [Scrollable] ancestor is found, then this method will assert in
+  /// debug mode, and throw an exception in release mode.
+  ///
+  /// See also:
+  ///
+  /// * [Scrollable.maybeOf], which is similar to this method, but returns null
+  ///   if no [Scrollable] ancestor is found.
+  static ScrollableState of(BuildContext context) {
+    final ScrollableState? scrollableState = maybeOf(context);
+    assert(() {
+      if (scrollableState == null) {
+        throw FlutterError(
+          'Scrollable.of() was called with a context that does not contain a '
+          'Scrollable widget.\n'
+          'No Scrollable widget ancestor could be found starting from the '
+          'context that was passed to Scrollable.of(). This can happen '
+          'because you are using a widget that looks for a Scrollable '
+          'ancestor, but no such ancestor exists.\n'
+          'The context used was:\n'
+          '  $context',
+        );
+      }
+      return true;
+    }());
+    return scrollableState!;
+  }
+
   /// Provides a heuristic to determine if expensive frame-bound tasks should be
   /// deferred for the [context] at a specific point in time.
   ///
@@ -343,7 +388,7 @@ class Scrollable extends StatefulWidget {
     // the `targetRenderObject` invisible.
     // Also see https://github.com/flutter/flutter/issues/65100
     RenderObject? targetRenderObject;
-    ScrollableState? scrollable = Scrollable.of(context);
+    ScrollableState? scrollable = Scrollable.maybeOf(context);
     while (scrollable != null) {
       futures.add(scrollable.position.ensureVisible(
         context.findRenderObject()!,
@@ -356,7 +401,7 @@ class Scrollable extends StatefulWidget {
 
       targetRenderObject = targetRenderObject ?? context.findRenderObject();
       context = scrollable.context;
-      scrollable = Scrollable.of(context);
+      scrollable = Scrollable.maybeOf(context);
     }
 
     if (futures.isEmpty || duration == Duration.zero) {
@@ -1618,11 +1663,11 @@ class ScrollAction extends Action<ScrollIntent> {
     final bool contextIsValid = focus != null && focus.context != null;
     if (contextIsValid) {
       // Check for primary scrollable within the current context
-      if (Scrollable.of(focus.context!) != null) {
+      if (Scrollable.maybeOf(focus.context!) != null) {
         return true;
       }
       // Check for fallback scrollable with context from PrimaryScrollController
-      final ScrollController? primaryScrollController = PrimaryScrollController.of(focus.context!);
+      final ScrollController? primaryScrollController = PrimaryScrollController.maybeOf(focus.context!);
       return primaryScrollController != null && primaryScrollController.hasClients;
     }
     return false;
@@ -1709,11 +1754,11 @@ class ScrollAction extends Action<ScrollIntent> {
 
   @override
   void invoke(ScrollIntent intent) {
-    ScrollableState? state = Scrollable.of(primaryFocus!.context!);
+    ScrollableState? state = Scrollable.maybeOf(primaryFocus!.context!);
     if (state == null) {
-      final ScrollController? primaryScrollController = PrimaryScrollController.of(primaryFocus!.context!);
+      final ScrollController primaryScrollController = PrimaryScrollController.of(primaryFocus!.context!);
       assert (() {
-        if (primaryScrollController!.positions.length != 1) {
+        if (primaryScrollController.positions.length != 1) {
           throw FlutterError.fromParts(<DiagnosticsNode>[
             ErrorSummary(
               'A ScrollAction was invoked with the PrimaryScrollController, but '
@@ -1735,11 +1780,11 @@ class ScrollAction extends Action<ScrollIntent> {
         return true;
       }());
 
-      if (primaryScrollController!.position.context.notificationContext == null
+      if (primaryScrollController.position.context.notificationContext == null
-          && Scrollable.of(primaryScrollController.position.context.notificationContext!) == null) {
+          && Scrollable.maybeOf(primaryScrollController.position.context.notificationContext!) == null) {
         return;
       }
-      state = Scrollable.of(primaryScrollController.position.context.notificationContext!);
+      state = Scrollable.maybeOf(primaryScrollController.position.context.notificationContext!);
     }
     assert(state != null, '$ScrollAction was invoked on a context that has no scrollable parent');
     assert(state!.position.hasPixels, 'Scrollable must be laid out before it can be scrolled via a ScrollAction');

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

@@ -1550,7 +1550,7 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
   }
 
   void _validateInteractions(AnimationStatus status) {
-    final ScrollController? scrollController = widget.controller ?? PrimaryScrollController.of(context);
+    final ScrollController? scrollController = widget.controller ?? PrimaryScrollController.maybeOf(context);
     if (status == AnimationStatus.dismissed) {
       assert(_fadeoutOpacityAnimation.value == 0.0);
       // We do not check for a valid scroll position if the scrollbar is not
@@ -1566,7 +1566,7 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
     if (!mounted) {
       return true;
     }
-    final ScrollController? scrollController = widget.controller ?? PrimaryScrollController.of(context);
+    final ScrollController? scrollController = widget.controller ?? PrimaryScrollController.maybeOf(context);
     final bool tryPrimary = widget.controller == null;
     final String controllerForError = tryPrimary
       ? 'PrimaryScrollController'
@@ -1788,7 +1788,7 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
   @mustCallSuper
   void handleThumbPressStart(Offset localPosition) {
     assert(_debugCheckHasValidScrollPosition());
-    _currentController = widget.controller ?? PrimaryScrollController.of(context);
+    _currentController = widget.controller ?? PrimaryScrollController.maybeOf(context);
     final Axis? direction = getScrollbarDirection();
     if (direction == null) {
       return;
@@ -1835,7 +1835,7 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
   void _handleTrackTapDown(TapDownDetails details) {
     // The Scrollbar should page towards the position of the tap on the track.
     assert(_debugCheckHasValidScrollPosition());
-    _currentController = widget.controller ?? PrimaryScrollController.of(context);
+    _currentController = widget.controller ?? PrimaryScrollController.maybeOf(context);
 
     final ScrollPosition position = _currentController!.position;
     if (!position.physics.shouldAcceptUserOffset(position)) {
@@ -1844,7 +1844,7 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
 
     double scrollIncrement;
     // Is an increment calculator available?
-    final ScrollIncrementCalculator? calculator = Scrollable.of(
+    final ScrollIncrementCalculator? calculator = Scrollable.maybeOf(
       _currentController!.position.context.notificationContext!,
     )?.widget.incrementCalculator;
     if (calculator != null) {
@@ -1893,7 +1893,7 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
   // ScrollController takes precedence over ScrollNotification
   bool _shouldUpdatePainter(Axis notificationAxis) {
     final ScrollController? scrollController = widget.controller ??
-        PrimaryScrollController.of(context);
+        PrimaryScrollController.maybeOf(context);
     // Only update the painter of this scrollbar if the notification
     // metrics do not conflict with the information we have from the scroll
     // controller.
@@ -1979,7 +1979,7 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
 
   Map<Type, GestureRecognizerFactory> get _gestures {
     final Map<Type, GestureRecognizerFactory> gestures = <Type, GestureRecognizerFactory>{};
-    final ScrollController? controller = widget.controller ?? PrimaryScrollController.of(context);
+    final ScrollController? controller = widget.controller ?? PrimaryScrollController.maybeOf(context);
     if (controller == null || !enableGestures) {
       return gestures;
     }

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

@@ -241,7 +241,7 @@ class SingleChildScrollView extends StatelessWidget {
         ?? controller == null && PrimaryScrollController.shouldInherit(context, scrollDirection);
 
     final ScrollController? scrollController = effectivePrimary
-        ? PrimaryScrollController.of(context)
+        ? PrimaryScrollController.maybeOf(context)
         : controller;
 
     Widget scrollable = Scrollable(

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

@@ -212,7 +212,7 @@ class _FloatingHeaderState extends State<_FloatingHeader> {
     if (_position != null) {
       _position!.isScrollingNotifier.removeListener(_isScrollingListener);
     }
-    _position = Scrollable.of(context)?.position;
+    _position = Scrollable.maybeOf(context)?.position;
     if (_position != null) {
       _position!.isScrollingNotifier.addListener(_isScrollingListener);
     }

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

@@ -245,19 +245,67 @@ class DefaultTextHeightBehavior extends InheritedTheme {
   /// {@macro dart.ui.textHeightBehavior}
   final TextHeightBehavior textHeightBehavior;
 
-  /// The closest instance of this class that encloses the given context.
+  /// The closest instance of [DefaultTextHeightBehavior] that encloses the
+  /// given context, or null if none is found.
   ///
   /// If no such instance exists, this method will return `null`.
   ///
+  /// Calling this method will create a dependency on the closest
+  /// [DefaultTextHeightBehavior] in the [context], if there is one.
+  ///
   /// Typical usage is as follows:
   ///
   /// ```dart
-  /// TextHeightBehavior defaultTextHeightBehavior = DefaultTextHeightBehavior.of(context)!;
+  /// TextHeightBehavior? defaultTextHeightBehavior = DefaultTextHeightBehavior.of(context);
   /// ```
-  static TextHeightBehavior? of(BuildContext context) {
+  ///
+  /// See also:
+  ///
+  /// * [DefaultTextHeightBehavior.maybeOf], which is similar to this method,
+  ///   but asserts if no [DefaultTextHeightBehavior] ancestor is found.
+  static TextHeightBehavior? maybeOf(BuildContext context) {
     return context.dependOnInheritedWidgetOfExactType<DefaultTextHeightBehavior>()?.textHeightBehavior;
   }
 
+  /// The closest instance of [DefaultTextHeightBehavior] that encloses the
+  /// given context.
+  ///
+  /// If no such instance exists, this method will assert in debug mode, and
+  /// throw an exception in release mode.
+  ///
+  /// Typical usage is as follows:
+  ///
+  /// ```dart
+  /// TextHeightBehavior defaultTextHeightBehavior = DefaultTextHeightBehavior.of(context);
+  /// ```
+  ///
+  /// Calling this method will create a dependency on the closest
+  /// [DefaultTextHeightBehavior] in the [context].
+  ///
+  /// See also:
+  ///
+  /// * [DefaultTextHeightBehavior.maybeOf], which is similar to this method,
+  ///   but returns null if no [DefaultTextHeightBehavior] ancestor is found.
+  static TextHeightBehavior of(BuildContext context) {
+    final TextHeightBehavior? behavior = maybeOf(context);
+    assert(() {
+      if (behavior == null) {
+        throw FlutterError(
+          'DefaultTextHeightBehavior.of() was called with a context that does not contain a '
+          'DefaultTextHeightBehavior widget.\n'
+          'No DefaultTextHeightBehavior widget ancestor could be found starting from the '
+          'context that was passed to DefaultTextHeightBehavior.of(). This can happen '
+          'because you are using a widget that looks for a DefaultTextHeightBehavior '
+          'ancestor, but no such ancestor exists.\n'
+          'The context used was:\n'
+          '  $context',
+        );
+      }
+      return true;
+    }());
+    return behavior!;
+  }
+
   @override
   bool updateShouldNotify(DefaultTextHeightBehavior oldWidget) {
     return textHeightBehavior != oldWidget.textHeightBehavior;
@@ -564,7 +612,7 @@ class Text extends StatelessWidget {
       maxLines: maxLines ?? defaultTextStyle.maxLines,
       strutStyle: strutStyle,
       textWidthBasis: textWidthBasis ?? defaultTextStyle.textWidthBasis,
-      textHeightBehavior: textHeightBehavior ?? defaultTextStyle.textHeightBehavior ?? DefaultTextHeightBehavior.of(context),
+      textHeightBehavior: textHeightBehavior ?? defaultTextStyle.textHeightBehavior ?? DefaultTextHeightBehavior.maybeOf(context),
       selectionRegistrar: registrar,
       selectionColor: selectionColor ?? DefaultSelectionStyle.of(context).selectionColor ?? DefaultSelectionStyle.defaultColor,
       text: TextSpan(

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

@@ -1893,7 +1893,7 @@ class TextSelectionGestureDetectorBuilder {
     final ScrollableState? scrollableState =
         delegate.editableTextKey.currentContext == null
             ? null
-            : Scrollable.of(delegate.editableTextKey.currentContext!);
+            : Scrollable.maybeOf(delegate.editableTextKey.currentContext!);
     return scrollableState == null
         ? 0.0
         : scrollableState.position.pixels;

packages/flutter/test/material/app_bar_test.dart

@@ -51,7 +51,7 @@ Widget buildSliverAppBarApp({
 }
 
 ScrollController primaryScrollController(WidgetTester tester) {
-  return PrimaryScrollController.of(tester.element(find.byType(CustomScrollView)))!;
+  return PrimaryScrollController.of(tester.element(find.byType(CustomScrollView)));
 }
 
 TextStyle? iconStyle(WidgetTester tester, IconData icon) {

packages/flutter/test/material/data_table_test.dart

@@ -1589,7 +1589,7 @@ void main() {
 
     final TestGesture gesture = await tester.startGesture(tester.getCenter(find.text('Content1')));
     await tester.pump(const Duration(milliseconds: 200)); // splash is well underway
-    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))! as RenderBox;
+    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))as RenderBox;
     expect(box, paints..circle(x: 68.0, y: 24.0, color: pressedColor));
     await gesture.up();
   });

packages/flutter/test/material/dropdown_test.dart

@@ -1011,7 +1011,7 @@ void main() {
     await tester.tap(find.byKey(buttonKey));
     await tester.pump();
 
-    final ScrollController scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)))!;
+    final ScrollController scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)));
     // Make sure there is no overscroll
     expect(scrollController.offset, scrollController.position.maxScrollExtent);
 
@@ -1854,7 +1854,7 @@ void main() {
 
     double getMenuScroll() {
       double scrollPosition;
-      final ScrollController scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)))!;
+      final ScrollController scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)));
       assert(scrollController != null);
       scrollPosition = scrollController.position.pixels;
       assert(scrollPosition != null);
@@ -1890,7 +1890,7 @@ void main() {
 
     double getMenuScroll() {
       double scrollPosition;
-      final ScrollController scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)))!;
+      final ScrollController scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)));
       assert(scrollController != null);
       scrollPosition = scrollController.position.pixels;
       assert(scrollPosition != null);
@@ -1927,7 +1927,7 @@ void main() {
 
     double getMenuScroll() {
       double scrollPosition;
-      final ScrollController scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)))!;
+      final ScrollController scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)));
       assert(scrollController != null);
       scrollPosition = scrollController.position.pixels;
       assert(scrollPosition != null);
@@ -1964,7 +1964,7 @@ void main() {
 
     double getMenuScroll() {
       double scrollPosition;
-      final ScrollController scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)))!;
+      final ScrollController scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)));
       assert(scrollController != null);
       scrollPosition = scrollController.position.pixels;
       assert(scrollPosition != null);
@@ -3066,7 +3066,7 @@ void main() {
     await tester.tap(find.text('0'));
     await tester.pumpAndSettle();
 
-    ScrollController scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)))!;
+    ScrollController scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)));
     // The scrollbar shouldn't show if the list fits into the screen.
     expect(scrollController.position.maxScrollExtent, 0);
     expect(find.byType(Scrollbar), isNot(paints..rect()));
@@ -3082,7 +3082,7 @@ void main() {
     await tester.tap(find.text('0'));
     await tester.pumpAndSettle();
 
-    scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)))!;
+    scrollController = PrimaryScrollController.of(tester.element(find.byType(ListView)));
     // The scrollbar is shown when the list is longer than the height of the screen.
     expect(scrollController.position.maxScrollExtent > 0, isTrue);
     expect(find.byType(Scrollbar), paints..rect());

packages/flutter/test/material/elevated_button_test.dart

@@ -1279,7 +1279,7 @@ void main() {
     await tester.pumpWidget(buildFrame(splashFactory: NoSplash.splashFactory));
     {
       final TestGesture gesture = await tester.startGesture(tester.getCenter(find.text('test')));
-      final MaterialInkController material = Material.of(tester.element(find.text('test')))!;
+      final MaterialInkController material = Material.of(tester.element(find.text('test')));
       await tester.pump(const Duration(milliseconds: 200));
       expect(material, paintsExactlyCountTimes(#drawCircle, 0));
       await gesture.up();
@@ -1290,7 +1290,7 @@ void main() {
     await tester.pumpWidget(buildFrame(splashFactory: InkRipple.splashFactory));
     {
       final TestGesture gesture = await tester.startGesture(tester.getCenter(find.text('test')));
-      final MaterialInkController material = Material.of(tester.element(find.text('test')))!;
+      final MaterialInkController material = Material.of(tester.element(find.text('test')));
       await tester.pump(const Duration(milliseconds: 200));
       expect(material, paintsExactlyCountTimes(#drawCircle, 1));
       await gesture.up();

packages/flutter/test/material/filled_button_test.dart

@@ -1307,7 +1307,7 @@ void main() {
     await tester.pumpWidget(buildFrame(splashFactory: NoSplash.splashFactory));
     {
       final TestGesture gesture = await tester.startGesture(tester.getCenter(find.text('test')));
-      final MaterialInkController material = Material.of(tester.element(find.text('test')))!;
+      final MaterialInkController material = Material.of(tester.element(find.text('test')));
       await tester.pump(const Duration(milliseconds: 200));
       expect(material, paintsExactlyCountTimes(#drawCircle, 0));
       await gesture.up();
@@ -1318,7 +1318,7 @@ void main() {
     await tester.pumpWidget(buildFrame(splashFactory: InkRipple.splashFactory));
     {
       final TestGesture gesture = await tester.startGesture(tester.getCenter(find.text('test')));
-      final MaterialInkController material = Material.of(tester.element(find.text('test')))!;
+      final MaterialInkController material = Material.of(tester.element(find.text('test')));
       await tester.pump(const Duration(milliseconds: 200));
       expect(material, paintsExactlyCountTimes(#drawCircle, 1));
       await gesture.up();

packages/flutter/test/material/ink_paint_test.dart

@@ -75,7 +75,7 @@ void main() {
     await tester.pump(); // start gesture
     await tester.pump(const Duration(milliseconds: 200)); // wait for splash to be well under way
 
-    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))! as RenderBox;
+    final RenderBox box = Material.of(tester.element(find.byType(InkWell))) as RenderBox;
     expect(
       box,
       paints
@@ -127,7 +127,7 @@ void main() {
     await tester.tapAt(tapDownOffset);
     await tester.pump(); // start gesture
 
-    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))! as RenderBox;
+    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))as RenderBox;
 
     bool offsetsAreClose(Offset a, Offset b) => (a - b).distance < 1.0;
     bool radiiAreClose(double a, double b) => (a - b).abs() < 1.0;
@@ -205,7 +205,7 @@ void main() {
     await tester.pump(); // start gesture
     await tester.pump(const Duration(milliseconds: 200)); // wait for splash to be well under way
 
-    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))! as RenderBox;
+    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))as RenderBox;
     expect(
       box,
       paints
@@ -337,7 +337,7 @@ void main() {
     await tester.sendKeyEvent(LogicalKeyboardKey.space);
     await tester.pump();
 
-    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))! as RenderBox;
+    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))as RenderBox;
 
     // ripplePattern always add a translation of topLeft.
     expect(box, ripplePattern(30.0, 0));
@@ -433,7 +433,7 @@ void main() {
     await gesture.moveTo(Offset.zero);
     await gesture.up(); // generates a tap cancel
 
-    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))! as RenderBox;
+    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))as RenderBox;
     expect(box, paints..everything((Symbol method, List<dynamic> arguments) {
       if (method != #drawCircle) {
         return true;

packages/flutter/test/material/ink_sparkle_test.dart

@@ -50,7 +50,7 @@ void main() {
     await tester.pump();
     await tester.pump(const Duration(milliseconds: 200));
 
-    final MaterialInkController material = Material.of(tester.element(buttonFinder))!;
+    final MaterialInkController material = Material.of(tester.element(buttonFinder));
     expect(material, paintsExactlyCountTimes(#drawRect, 1));
 
     // ignore: avoid_dynamic_calls
@@ -81,7 +81,7 @@ void main() {
     await tester.pump();
     await tester.pump(const Duration(milliseconds: 200));
 
-    final MaterialInkController material = Material.of(tester.element(buttonFinder))!;
+    final MaterialInkController material = Material.of(tester.element(buttonFinder));
     expect(material, paintsExactlyCountTimes(#drawPaint, 1));
   },
     skip: kIsWeb, // [intended] shaders are not yet supported for web.

packages/flutter/test/material/ink_splash_test.dart

@@ -48,7 +48,7 @@ void main() {
     await tester.pumpWidget(buildFrame(splashFactory: NoSplash.splashFactory));
     {
       final TestGesture gesture = await tester.startGesture(tester.getCenter(find.text('test')));
-      final MaterialInkController material = Material.of(tester.element(find.text('test')))!;
+      final MaterialInkController material = Material.of(tester.element(find.text('test')));
       await tester.pump(const Duration(milliseconds: 200));
       expect(material, paintsExactlyCountTimes(#drawCircle, 0));
       await gesture.up();
@@ -59,7 +59,7 @@ void main() {
     await tester.pumpWidget(buildFrame());
     {
       final TestGesture gesture = await tester.startGesture(tester.getCenter(find.text('test')));
-      final MaterialInkController material = Material.of(tester.element(find.text('test')))!;
+      final MaterialInkController material = Material.of(tester.element(find.text('test')));
       await tester.pump(const Duration(milliseconds: 200));
       expect(material, paintsExactlyCountTimes(#drawCircle, 1));
       await gesture.up();

packages/flutter/test/material/ink_well_test.dart

@@ -865,7 +865,7 @@ void main() {
         ),
       ),
     );
-    final MaterialInkController material = Material.of(tester.element(find.byKey(innerKey)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byKey(innerKey)));
 
     // Press
     final TestGesture gesture = await tester.startGesture(tester.getCenter(find.byKey(innerKey)), pointer: 1);
@@ -938,7 +938,7 @@ void main() {
         ),
       ),
     );
-    final MaterialInkController material = Material.of(tester.element(find.byKey(innerKey)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byKey(innerKey)));
 
     // Press
     final TestGesture gesture = await tester.startGesture(tester.getCenter(find.byKey(innerKey)), pointer: 1);
@@ -1019,7 +1019,7 @@ void main() {
         ),
       ),
     );
-    final MaterialInkController material = Material.of(tester.element(find.byKey(innerKey)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byKey(innerKey)));
 
     // Press middle
     await tester.startGesture(tester.getTopLeft(find.byKey(middleKey)) + const Offset(1, 1), pointer: 1);
@@ -1079,7 +1079,7 @@ void main() {
         ),
       ),
     );
-    final MaterialInkController material = Material.of(tester.element(find.byKey(leftKey)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byKey(leftKey)));
 
     final Offset parentPosition = tester.getTopLeft(find.byKey(parentKey)) + const Offset(1, 1);
 
@@ -1191,7 +1191,7 @@ void main() {
         ),
       ),
     );
-    final MaterialInkController material = Material.of(tester.element(find.byKey(innerKey)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byKey(innerKey)));
 
     // Press inner
     final TestGesture gesture = await tester.startGesture(const Offset(100, 50), pointer: 1);
@@ -1265,7 +1265,7 @@ void main() {
         ),
       ),
     );
-    final MaterialInkController material = Material.of(tester.element(find.byKey(innerKey)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byKey(innerKey)));
 
     // Press
     final TestGesture gesture = await tester.startGesture(tester.getCenter(find.byKey(innerKey)), pointer: 1);

packages/flutter/test/material/material_test.dart

@@ -1006,7 +1006,7 @@ void main() {
         child: SizedBox(key: sizedBoxKey, width: 20, height: 20),
       ),
     ));
-    final MaterialInkController controller = Material.of(sizedBoxKey.currentContext!)!;
+    final MaterialInkController controller = Material.of(sizedBoxKey.currentContext!);
 
     final TrackPaintInkFeature tracker = TrackPaintInkFeature(
       controller: controller,
@@ -1015,7 +1015,7 @@ void main() {
     controller.addInkFeature(tracker);
     expect(tracker.paintCount, 0);
 
-    // Force a repaint. Since it's offstage, the ink feture should not get painted.
+    // Force a repaint. Since it's offstage, the ink feature should not get painted.
     materialKey.currentContext!.findRenderObject()!.paint(PaintingContext(ContainerLayer(), Rect.largest), Offset.zero);
     expect(tracker.paintCount, 0);
 

packages/flutter/test/material/outlined_button_test.dart

@@ -1442,7 +1442,7 @@ void main() {
     await tester.pumpWidget(buildFrame(splashFactory: NoSplash.splashFactory));
     {
       final TestGesture gesture = await tester.startGesture(tester.getCenter(find.text('test')));
-      final MaterialInkController material = Material.of(tester.element(find.text('test')))!;
+      final MaterialInkController material = Material.of(tester.element(find.text('test')));
       await tester.pump(const Duration(milliseconds: 200));
       expect(material, paintsExactlyCountTimes(#drawCircle, 0));
       await gesture.up();
@@ -1453,7 +1453,7 @@ void main() {
     await tester.pumpWidget(buildFrame(splashFactory: InkRipple.splashFactory));
     {
       final TestGesture gesture = await tester.startGesture(tester.getCenter(find.text('test')));
-      final MaterialInkController material = Material.of(tester.element(find.text('test')))!;
+      final MaterialInkController material = Material.of(tester.element(find.text('test')));
       await tester.pump(const Duration(milliseconds: 200));
       expect(material, paintsExactlyCountTimes(#drawCircle, 1));
       await gesture.up();

packages/flutter/test/material/raw_material_button_test.dart

@@ -32,7 +32,7 @@ void main() {
     await tester.tap(find.text('BUTTON'));
     await tester.pump(const Duration(milliseconds: 10));
 
-    final RenderBox splash = Material.of(tester.element(find.byType(InkWell)))! as RenderBox;
+    final RenderBox splash = Material.of(tester.element(find.byType(InkWell))) as RenderBox;
     expect(splash, paints..circle(color: splashColor));
 
     await tester.pumpAndSettle();
@@ -72,7 +72,7 @@ void main() {
     await tester.pump(const Duration(milliseconds: 10));
 
     if (!kIsWeb) {
-      final RenderBox splash = Material.of(tester.element(find.byType(InkWell)))! as RenderBox;
+      final RenderBox splash = Material.of(tester.element(find.byType(InkWell))) as RenderBox;
       expect(splash, paints..circle(color: splashColor));
     }
 
@@ -90,7 +90,7 @@ void main() {
     await tester.sendKeyEvent(LogicalKeyboardKey.space);
     await tester.pump(const Duration(milliseconds: 10));
 
-    final RenderBox splash = Material.of(tester.element(find.byType(InkWell)))! as RenderBox;
+    final RenderBox splash = Material.of(tester.element(find.byType(InkWell))) as RenderBox;
     expect(splash, paints..circle(color: splashColor));
 
     await tester.pumpAndSettle();
@@ -195,7 +195,7 @@ void main() {
     await tester.pump(); // start gesture
     await tester.pump(const Duration(milliseconds: 200)); // wait for splash to be well under way
 
-    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))! as RenderBox;
+    final RenderBox box = Material.of(tester.element(find.byType(InkWell))) as RenderBox;
     // centered in material button.
     expect(box, paints..circle(x: 44.0, y: 18.0, color: splashColor));
     await gesture.up();
@@ -226,7 +226,7 @@ void main() {
     final TestGesture gesture = await tester.startGesture(top);
     await tester.pump(); // start gesture
     await tester.pump(const Duration(milliseconds: 200)); // wait for splash to be well under way
-    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))! as RenderBox;
+    final RenderBox box = Material.of(tester.element(find.byType(InkWell))) as RenderBox;
     // paints above material
     expect(box, paints..circle(x: 44.0, y: 0.0, color: splashColor));
     await gesture.up();
@@ -326,7 +326,7 @@ void main() {
         ),
       ),
     );
-    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))! as RenderBox;
+    final RenderBox box = Material.of(tester.element(find.byType(InkWell))) as RenderBox;
     expect(box, isNot(paints..rect(color: focusColor)));
 
     focusNode.requestFocus();
@@ -425,7 +425,7 @@ void main() {
         ),
       ),
     );
-    final RenderBox box = Material.of(tester.element(find.byType(InkWell)))! as RenderBox;
+    final RenderBox box = Material.of(tester.element(find.byType(InkWell))) as RenderBox;
     final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
     await gesture.addPointer();
     expect(box, isNot(paints..rect(color: hoverColor)));

packages/flutter/test/material/slider_test.dart

@@ -1000,7 +1000,7 @@ void main() {
       ),
     );
 
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     // 5 tick marks and a thumb.
     expect(material, paintsExactlyCountTimes(#drawCircle, 6));
@@ -1056,7 +1056,7 @@ void main() {
     }
 
     Future<void> testReparenting(bool reparent) async {
-      final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+      final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
       final Offset center = tester.getCenter(find.byType(Slider));
       // Move to 0.0.
       TestGesture gesture = await tester.startGesture(Offset.zero);
@@ -2030,7 +2030,7 @@ void main() {
     await tester.pumpWidget(buildApp());
     await tester.pumpAndSettle();
 
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
     // Check that thumb color is using active color.
     expect(material, paints..circle(color: activeColor));
 
@@ -2989,7 +2989,7 @@ void main() {
     await tester.pumpAndSettle();
 
     final MaterialInkController material =
-        Material.of(tester.element(find.byType(Slider)))!;
+        Material.of(tester.element(find.byType(Slider)));
     expect(material, paints..circle(color: color));
   });
 
@@ -3012,7 +3012,7 @@ void main() {
     await tester.pumpAndSettle();
 
     final MaterialInkController material =
-        Material.of(tester.element(find.byType(Slider)))!;
+        Material.of(tester.element(find.byType(Slider)));
     expect(material, paints..circle(color: color));
   });
 
@@ -3032,7 +3032,7 @@ void main() {
     await tester.pumpAndSettle();
 
     final MaterialInkController material =
-        Material.of(tester.element(find.byType(CupertinoSlider)))!;
+        Material.of(tester.element(find.byType(CupertinoSlider)));
     expect(
       material,
       paints
@@ -3064,7 +3064,7 @@ void main() {
     await tester.pumpAndSettle();
 
     final MaterialInkController material =
-        Material.of(tester.element(find.byType(CupertinoSlider)))!;
+        Material.of(tester.element(find.byType(CupertinoSlider)));
     expect(
       material,
       paints..rrect()..rrect()..rrect()..rrect()..rrect()..rrect(color: color),

packages/flutter/test/material/slider_theme_test.dart

@@ -163,7 +163,7 @@ void main() {
 
       await tester.pumpWidget(buildApp());
 
-      final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+      final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
       final RenderBox valueIndicatorBox = tester.renderObject(find.byType(Overlay));
 
       // Check default theme for enabled widget.
@@ -356,7 +356,7 @@ void main() {
     );
 
     await tester.pumpWidget(_buildApp(sliderTheme, value: 0.5, secondaryTrackValue: 0.75, enabled: false));
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     expect(
       material,
@@ -380,7 +380,7 @@ void main() {
     );
 
     await tester.pumpWidget(_buildApp(sliderTheme, value: 0.5, secondaryTrackValue: 0.75, enabled: false));
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     expect(
       material,
@@ -487,7 +487,7 @@ void main() {
     final SliderThemeData sliderTheme = theme.sliderTheme.copyWith(thumbColor: Colors.red.shade500);
 
     await tester.pumpWidget(_buildApp(sliderTheme, value: 0.25, secondaryTrackValue: 0.5));
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     const Radius radius = Radius.circular(2);
     const Radius activatedRadius = Radius.circular(3);
@@ -523,7 +523,7 @@ void main() {
     final SliderThemeData sliderTheme = theme.sliderTheme.copyWith(thumbColor: Colors.red.shade500);
 
     await tester.pumpWidget(_buildApp(sliderTheme, value: 0.25));
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     // With no touch, paints only the thumb.
     expect(
@@ -643,7 +643,7 @@ void main() {
     final SliderThemeData sliderTheme = theme.sliderTheme.copyWith(thumbColor: Colors.red.shade500);
 
     await tester.pumpWidget(_buildApp(sliderTheme, value: 0.45));
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     expect(material, paints..circle(color: sliderTheme.thumbColor, radius: 10.0));
 
@@ -1050,7 +1050,7 @@ void main() {
 
     await tester.pumpWidget(_buildApp(sliderTheme, value: 0.25));
 
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     // Top and bottom are centerY (300) + and - trackRadius (8).
     expect(
@@ -1082,7 +1082,7 @@ void main() {
     );
 
     await tester.pumpWidget(_buildApp(sliderTheme, value: 0.25));
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     expect(
       material,
@@ -1106,7 +1106,7 @@ void main() {
     );
 
     await tester.pumpWidget(_buildApp(sliderTheme, value: 0.25));
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     expect(
       material,
@@ -1132,7 +1132,7 @@ void main() {
 
     await tester.pumpWidget(_buildApp(sliderTheme, value: 0.5, divisions: 2));
 
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     expect(
       material,
@@ -1168,7 +1168,7 @@ void main() {
     await tester.startGesture(center);
     await tester.pumpAndSettle();
 
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
     expect(
       material,
       paints..circle(
@@ -1190,7 +1190,7 @@ void main() {
 
     final MaterialInkController material = Material.of(
       tester.element(find.byType(Slider)),
-    )!;
+    );
 
     // The track rectangle begins at 10 pixels from the left of the screen and ends 10 pixels from the right
     // (790 pixels from the left). The main check here it that the track itself should be centered on
@@ -1242,7 +1242,7 @@ void main() {
       divisions: 4,
     ));
 
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     expect(material, paintsExactlyCountTimes(#drawRect, 0));
     expect(material, paintsExactlyCountTimes(#drawCircle, 0));
@@ -1262,7 +1262,7 @@ void main() {
       divisions: 4,
     ));
 
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     // Only 2 track segments.
     expect(material, paintsExactlyCountTimes(#drawRRect, 2));
@@ -1286,7 +1286,7 @@ void main() {
       divisions: 4,
     ));
 
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     // Only 5 tick marks.
     expect(material, paintsExactlyCountTimes(#drawRect, 0));
@@ -1309,7 +1309,7 @@ void main() {
         divisions: 4,
       ));
 
-      final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+      final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
       // Only 1 thumb.
       expect(material, paintsExactlyCountTimes(#drawRect, 0));
@@ -1333,7 +1333,7 @@ void main() {
       divisions: 4,
     ));
 
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
 
     // Tap the center of the track and wait for animations to finish.
     final Offset center = tester.getCenter(find.byType(Slider));
@@ -1362,7 +1362,7 @@ void main() {
       divisions: 4,
     ));
 
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
     final RenderBox valueIndicatorBox = tester.renderObject(find.byType(Overlay));
 
     // Tap the center of the track and wait for animations to finish.
@@ -1393,7 +1393,7 @@ void main() {
       divisions: 4,
     ));
 
-    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)))!;
+    final MaterialInkController material = Material.of(tester.element(find.byType(Slider)));
     final RenderBox valueIndicatorBox = tester.renderObject(find.byType(Overlay));
 
     // Tap the center of the track to kick off the animation of the value indicator.

packages/flutter/test/material/tabs_test.dart

@@ -364,7 +364,7 @@ void main() {
     expect(find.text('A'), findsOneWidget);
     expect(find.text('B'), findsOneWidget);
     expect(find.text('C'), findsOneWidget);
-    final TabController controller = DefaultTabController.of(tester.element(find.text('A')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('A')));
     expect(controller, isNotNull);
     expect(controller.index, 2);
     expect(controller.previousIndex, 2);
@@ -400,7 +400,7 @@ void main() {
     expect(find.text('A'), findsOneWidget);
     expect(find.text('B'), findsOneWidget);
     expect(find.text('C'), findsOneWidget);
-    final TabController controller = DefaultTabController.of(tester.element(find.text('A')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('A')));
     expect(controller.index, 2);
     expect(controller.previousIndex, 2);
 
@@ -421,7 +421,7 @@ void main() {
     final List<String> tabs = <String>['AAAAAA', 'BBBBBB', 'CCCCCC', 'DDDDDD', 'EEEEEE', 'FFFFFF', 'GGGGGG', 'HHHHHH', 'IIIIII', 'JJJJJJ', 'KKKKKK', 'LLLLLL'];
     const Key tabBarKey = Key('TabBar');
     await tester.pumpWidget(buildFrame(tabs: tabs, value: 'AAAAAA', isScrollable: true, tabBarKey: tabBarKey));
-    final TabController controller = DefaultTabController.of(tester.element(find.text('AAAAAA')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('AAAAAA')));
     expect(controller, isNotNull);
     expect(controller.index, 0);
 
@@ -442,7 +442,7 @@ void main() {
     const Key tabBarKey = Key('TabBar');
     const EdgeInsetsGeometry padding = EdgeInsets.only(right: 30, left: 60);
     await tester.pumpWidget(buildFrame(tabs: tabs, value: 'AAAAAA', isScrollable: true, tabBarKey: tabBarKey, padding: padding));
-    final TabController controller = DefaultTabController.of(tester.element(find.text('AAAAAA')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('AAAAAA')));
     expect(controller, isNotNull);
     expect(controller.index, 0);
 
@@ -470,7 +470,7 @@ void main() {
       padding: padding,
       textDirection: TextDirection.rtl,
     ));
-    final TabController controller = DefaultTabController.of(tester.element(find.text('AAAAAA')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('AAAAAA')));
     expect(controller, isNotNull);
     expect(controller.index, 0);
 
@@ -489,7 +489,7 @@ void main() {
     final List<String> tabs = <String>['AAAA', 'BBBB', 'CCCC', 'DDDD', 'EEEE', 'FFFF', 'GGGG', 'HHHH', 'IIII', 'JJJJ', 'KKKK', 'LLLL'];
     const Key tabBarKey = Key('TabBar');
     await tester.pumpWidget(buildFrame(tabs: tabs, value: 'AAAA', isScrollable: true, tabBarKey: tabBarKey));
-    final TabController controller = DefaultTabController.of(tester.element(find.text('AAAA')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('AAAA')));
     expect(controller, isNotNull);
     expect(controller.index, 0);
 
@@ -529,7 +529,7 @@ void main() {
     }
 
     await tester.pumpWidget(builder());
-    final TabController controller = DefaultTabController.of(tester.element(find.text('AAAAAA')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('AAAAAA')));
 
     TestGesture gesture = await tester.startGesture(tester.getCenter(find.text(tabs[0])));
     await gesture.moveBy(const Offset(-600.0, 0.0));
@@ -586,7 +586,7 @@ void main() {
     expect(find.text('LEFT CHILD'), findsOneWidget);
     expect(find.text('RIGHT CHILD'), findsNothing);
 
-    final TabController controller = DefaultTabController.of(tester.element(find.text('LEFT')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('LEFT')));
     expect(controller.index, 0);
 
     // Fling to the left, switch from the 'LEFT' tab to the 'RIGHT'
@@ -615,7 +615,7 @@ void main() {
     expect(find.text('LEFT CHILD'), findsOneWidget);
     expect(find.text('RIGHT CHILD'), findsNothing);
 
-    final TabController controller = DefaultTabController.of(tester.element(find.text('LEFT')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('LEFT')));
     expect(controller.index, 0);
 
     final Offset flingStart = tester.getCenter(find.text('LEFT CHILD'));
@@ -636,7 +636,7 @@ void main() {
     expect(find.text('LEFT CHILD'), findsOneWidget);
     expect(find.text('RIGHT CHILD'), findsNothing);
 
-    final TabController controller = DefaultTabController.of(tester.element(find.text('LEFT')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('LEFT')));
     expect(controller.index, 0);
 
     final Offset flingStart = tester.getCenter(find.text('LEFT CHILD'));
@@ -659,7 +659,7 @@ void main() {
     expect(find.text('LEFT CHILD'), findsOneWidget);
     expect(find.text('RIGHT CHILD'), findsNothing);
 
-    final TabController controller = DefaultTabController.of(tester.element(find.text('LEFT')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('LEFT')));
     expect(controller.index, 0);
 
     final Offset flingStart = tester.getCenter(find.text('LEFT CHILD'));
@@ -772,7 +772,7 @@ void main() {
     final List<String> tabs = <String>['LEFT', 'RIGHT'];
 
     await tester.pumpWidget(buildLeftRightApp(tabs: tabs, value: 'LEFT'));
-    final TabController controller = DefaultTabController.of(tester.element(find.text('LEFT')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('LEFT')));
 
     expect(controller, isNotNull);
     expect(controller.index, 0);
@@ -1013,7 +1013,7 @@ void main() {
     final List<String> tabs = <String>['A', 'B', 'C'];
 
     await tester.pumpWidget(buildFrame(tabs: tabs, value: 'B', animationDuration: animationDuration));
-    final TabController controller = DefaultTabController.of(tester.element(find.text('A')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('A')));
 
     await tester.tap(find.text('A'));
     await tester.pump();
@@ -1241,7 +1241,7 @@ void main() {
     final List<String> tabs = <String>['A', 'B', 'C'];
 
     await tester.pumpWidget(buildFrame(tabs: tabs, value: 'B', animationDuration: Duration.zero));
-    final TabController controller = DefaultTabController.of(tester.element(find.text('A')))!;
+    final TabController controller = DefaultTabController.of(tester.element(find.text('A')));
 
     await tester.tap(find.text('A'));
     await tester.pump();
@@ -1288,7 +1288,7 @@ void main() {
     }
 
     await tester.pumpWidget(buildWithTabBarView());
-    TabController controller = DefaultTabController.of(tester.element(find.text('A')))!;
+    TabController controller = DefaultTabController.of(tester.element(find.text('A')));
     expect(controller.index, 0);
 
     tabs.add('B');
@@ -1297,7 +1297,7 @@ void main() {
     await tester.pumpWidget(buildWithTabBarView());
     await tester.tap(find.text('C'));
     await tester.pumpAndSettle();
-    controller = DefaultTabController.of(tester.element(find.text('A')))!;
+    controller = DefaultTabController.of(tester.element(find.text('A')));
     expect(controller.index, 2);
 
     expect(tester.takeException(), isNull);
@@ -3752,7 +3752,7 @@ void main() {
         ),
       );
     }
-    TabController getController() => DefaultTabController.of(tester.element(find.text('A')))!;
+    TabController getController() => DefaultTabController.of(tester.element(find.text('A')));
 
     await tester.pumpWidget(buildTabs(threeTabs));
     await tester.tap(find.text('B'));
@@ -4346,7 +4346,7 @@ void main() {
       ),
     );
 
-    TabController getController() => DefaultTabController.of(tester.element(find.text('B')))!;
+    TabController getController() => DefaultTabController.of(tester.element(find.text('B')));
     TabController controller = getController();
 
     controller.animateTo(2, duration: const Duration(milliseconds: 200), curve: Curves.linear);

packages/flutter/test/material/text_button_test.dart

@@ -1249,7 +1249,7 @@ void main() {
     await tester.pumpWidget(buildFrame(splashFactory: NoSplash.splashFactory));
     {
       final TestGesture gesture = await tester.startGesture(tester.getCenter(find.text('test')));
-      final MaterialInkController material = Material.of(tester.element(find.text('test')))!;
+      final MaterialInkController material = Material.of(tester.element(find.text('test')));
       await tester.pump(const Duration(milliseconds: 200));
       expect(material, paintsExactlyCountTimes(#drawCircle, 0));
       await gesture.up();
@@ -1260,7 +1260,7 @@ void main() {
     await tester.pumpWidget(buildFrame(splashFactory: InkRipple.splashFactory));
     {
       final TestGesture gesture = await tester.startGesture(tester.getCenter(find.text('test')));
-      final MaterialInkController material = Material.of(tester.element(find.text('test')))!;
+      final MaterialInkController material = Material.of(tester.element(find.text('test')));
       await tester.pump(const Duration(milliseconds: 200));
       expect(material, paintsExactlyCountTimes(#drawCircle, 1));
       await gesture.up();

packages/flutter/test/widgets/default_text_height_behavior_test.dart

@@ -116,7 +116,7 @@ void main() {
 
       await tester.pumpWidget(Builder(
         builder: (BuildContext context) {
-          textHeightBehavior = DefaultTextHeightBehavior.of(context);
+          textHeightBehavior = DefaultTextHeightBehavior.maybeOf(context);
           return textWidget;
         },
       ));

packages/flutter/test/widgets/linked_scroll_view_test.dart

@@ -286,8 +286,8 @@ class _TestState extends State<Test> {
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
-    _beforeController.setParent(PrimaryScrollController.of(context));
+    _beforeController.setParent(PrimaryScrollController.maybeOf(context));
-    _afterController.setParent(PrimaryScrollController.of(context));
+    _afterController.setParent(PrimaryScrollController.maybeOf(context));
   }
 
   @override

packages/flutter/test/widgets/list_view_misc_test.dart

@@ -215,7 +215,7 @@ void main() {
     await tester.pumpWidget(buildFrame());
     expect(find.text('top'), findsOneWidget);
 
-    final ScrollPosition position = Scrollable.of(tester.element(find.text('middle')))!.position;
+    final ScrollPosition position = Scrollable.of(tester.element(find.text('middle'))).position;
     expect(position.viewportDimension, 600.0);
     expect(position.pixels, 0.0);
 

packages/flutter/test/widgets/page_storage_test.dart

@@ -16,7 +16,7 @@ void main() {
         home: StatefulBuilder(
           key: builderKey,
           builder: (BuildContext context, StateSetter setter) {
-            PageStorage.of(context)!.writeState(context, storedValue);
+            PageStorage.of(context).writeState(context, storedValue);
             setState = setter;
             return Center(
               child: Text('storedValue: $storedValue'),
@@ -28,13 +28,13 @@ void main() {
 
     final Element builderElement = tester.element(find.byKey(builderKey));
     expect(PageStorage.of(builderElement), isNotNull);
-    expect(PageStorage.of(builderElement)!.readState(builderElement), equals(storedValue));
+    expect(PageStorage.of(builderElement).readState(builderElement), equals(storedValue));
 
     setState(() {
       storedValue = 1;
     });
     await tester.pump();
-    expect(PageStorage.of(builderElement)!.readState(builderElement), equals(storedValue));
+    expect(PageStorage.of(builderElement).readState(builderElement), equals(storedValue));
   });
 
   testWidgets('PageStorage read and write by identifier', (WidgetTester tester) async {
@@ -46,7 +46,7 @@ void main() {
         home: StatefulBuilder(
           key: key,
           builder: (BuildContext context, StateSetter setter) {
-            PageStorage.of(context)!.writeState(context, storedValue, identifier: 123);
+            PageStorage.of(context).writeState(context, storedValue, identifier: 123);
             setState = setter;
             return Center(
               child: Text('storedValue: $storedValue'),
@@ -60,8 +60,8 @@ void main() {
     await tester.pumpWidget(buildWidthKey(key));
     Element builderElement = tester.element(find.byKey(key));
     expect(PageStorage.of(builderElement), isNotNull);
-    expect(PageStorage.of(builderElement)!.readState(builderElement), isNull);
+    expect(PageStorage.of(builderElement).readState(builderElement), isNull);
-    expect(PageStorage.of(builderElement)!.readState(builderElement, identifier: 123), equals(storedValue));
+    expect(PageStorage.of(builderElement).readState(builderElement, identifier: 123), equals(storedValue));
 
     // New StatefulBuilder widget - different key - but the same PageStorage identifier.
 
@@ -69,14 +69,14 @@ void main() {
     await tester.pumpWidget(buildWidthKey(key));
     builderElement = tester.element(find.byKey(key));
     expect(PageStorage.of(builderElement), isNotNull);
-    expect(PageStorage.of(builderElement)!.readState(builderElement), isNull);
+    expect(PageStorage.of(builderElement).readState(builderElement), isNull);
-    expect(PageStorage.of(builderElement)!.readState(builderElement, identifier: 123), equals(storedValue));
+    expect(PageStorage.of(builderElement).readState(builderElement, identifier: 123), equals(storedValue));
 
     setState(() {
       storedValue = 1;
     });
     await tester.pump();
-    expect(PageStorage.of(builderElement)!.readState(builderElement, identifier: 123), equals(storedValue));
+    expect(PageStorage.of(builderElement).readState(builderElement, identifier: 123), equals(storedValue));
   });
 
 }

packages/flutter/test/widgets/restoration.dart

@@ -21,7 +21,7 @@ class BucketSpyState extends State<BucketSpy> {
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
-    bucket = RestorationScope.of(context);
+    bucket = RestorationScope.maybeOf(context);
   }
 
   @override

packages/flutter/test/widgets/scroll_aware_image_provider_test.dart

@@ -22,11 +22,11 @@ void main() {
   });
 
   T findPhysics<T extends ScrollPhysics>(WidgetTester tester) {
-    return Scrollable.of(find.byType(TestWidget).evaluate().first)!.position.physics as T;
+    return Scrollable.of(find.byType(TestWidget).evaluate().first).position.physics as T;
   }
 
   ScrollMetrics findMetrics(WidgetTester tester) {
-    return Scrollable.of(find.byType(TestWidget).evaluate().first)!.position;
+    return Scrollable.of(find.byType(TestWidget).evaluate().first).position;
   }
 
   testWidgets('ScrollAwareImageProvider does not delay if widget is not in scrollable', (WidgetTester tester) async {

packages/flutter/test/widgets/scroll_behavior_test.dart

@@ -50,7 +50,7 @@ void main() {
       child: Builder(
         builder: (BuildContext context) {
           behavior = ScrollConfiguration.of(context) as TestScrollBehavior;
-          position = Scrollable.of(context)!.position as ScrollPositionWithSingleContext;
+          position = Scrollable.of(context).position as ScrollPositionWithSingleContext;
           return Container(height: 1000.0);
         },
       ),

packages/flutter/test/widgets/scroll_notification_test.dart

@@ -218,7 +218,7 @@ void main() {
       ScrollNotificationObserver(
         child: Builder(
           builder: (BuildContext context) {
-            observer = ScrollNotificationObserver.of(context)!;
+            observer = ScrollNotificationObserver.of(context);
             return const SingleChildScrollView(
               child: SizedBox(height: 1200.0),
             );

packages/flutter/test/widgets/scroll_view_test.dart

@@ -1478,7 +1478,7 @@ void main() {
     );
     final ScrollController controller = PrimaryScrollController.of(
       tester.element(find.byType(CustomScrollView)),
-    )!;
+    );
     await tester.pumpAndSettle();
     expect(controller.position.pixels, equals(0.0));
     expect(

packages/flutter/test/widgets/scrollable_of_test.dart

@@ -22,7 +22,7 @@ class _ScrollPositionListenerState extends State<ScrollPositionListener> {
   void didChangeDependencies() {
     super.didChangeDependencies();
     _position?.removeListener(listener);
-    _position = Scrollable.of(context)?.position;
+    _position = Scrollable.maybeOf(context)?.position;
     _position?.addListener(listener);
     widget.log('didChangeDependencies ${_position?.pixels.toStringAsFixed(1)}');
   }

packages/flutter/test/widgets/scrollable_test.dart

@@ -941,7 +941,7 @@ void main() {
     // Getting the tester to simulate a life-like fling is difficult.
     // Instead, just manually drive the activity with a ballistic simulation as
     // if the user has flung the list.
-    Scrollable.of(find.byType(SizedBox).evaluate().first)!.position.activity!.delegate.goBallistic(4000);
+    Scrollable.of(find.byType(SizedBox).evaluate().first).position.activity!.delegate.goBallistic(4000);
 
     await tester.pumpAndSettle();
     expect(find.byKey(const ValueKey<String>('Box 0')), findsNothing);
@@ -970,7 +970,7 @@ void main() {
     ));
     await tester.pumpAndSettle();
 
-    final ScrollPosition position = Scrollable.of(find.byType(SizedBox).evaluate().first)!.position;
+    final ScrollPosition position = Scrollable.of(find.byType(SizedBox).evaluate().first).position;
     final SuperPessimisticScrollPhysics physics = position.physics as SuperPessimisticScrollPhysics;
 
     expect(find.byKey(const ValueKey<String>('Box 0')), findsOneWidget);
@@ -1014,7 +1014,7 @@ void main() {
     ));
     await tester.pumpAndSettle();
 
-    final ScrollPosition position = Scrollable.of(find.byType(SizedBox).evaluate().first)!.position;
+    final ScrollPosition position = Scrollable.of(find.byType(SizedBox).evaluate().first).position;
 
     expect(find.byKey(const ValueKey<String>('Cheap box 0')), findsOneWidget);
     expect(find.byKey(const ValueKey<String>('Cheap box 52')), findsNothing);

packages/flutter/test/widgets/shortcuts_test.dart

@@ -1028,7 +1028,7 @@ void main() {
       );
       final ScrollController controller = PrimaryScrollController.of(
         tester.element(find.byType(ListView)),
-      )!;
+      );
       expect(controller.position.pixels, 0.0);
       expect(value, isTrue);