Use .fromMap() constructors in example code (#152535)

Currently, there are 21 `.resolveWith()` calls in example files.

This pull request changes 11 of them to use the new `.fromMap()` constructor. (Seven of them are now `const`!)

```dart
ListTile(
  iconColor: WidgetStateColor.fromMap(<WidgetStatesConstraint, Color>{
    WidgetState.disabled: Colors.red,
    WidgetState.selected: Colors.green,
    WidgetState.any:      Colors.black,
  }),
  // The same can be achieved using the .resolveWith() constructor.
  // The text color will be identical to the icon color above.
  textColor: WidgetStateColor.resolveWith((Set<WidgetState> states) {
    if (states.contains(WidgetState.disabled)) {
      return Colors.red;
    }
    if (states.contains(WidgetState.selected)) {
      return Colors.green;
    }
    return Colors.black;
  }),
),
```

examples/api/lib/material/input_decorator/input_decoration.widget_state.0.dart

@@ -32,12 +32,12 @@ class MaterialStateExample extends StatelessWidget {
       initialValue: 'abc',
       decoration: InputDecoration(
         prefixIcon: const Icon(Icons.person),
-        prefixIconColor: WidgetStateColor.resolveWith((Set<WidgetState> states) {
-          if (states.contains(WidgetState.focused)) {
-            return Colors.green;
-          }
-          return Colors.grey;
-        }),
+        prefixIconColor: WidgetStateColor.fromMap(
+          <WidgetStatesConstraint, Color>{
+            WidgetState.focused: Colors.green,
+            WidgetState.any:     Colors.grey,
+          },
+        ),
       ),
     );
   }

examples/api/lib/material/input_decorator/input_decoration.widget_state.1.dart

@@ -32,15 +32,11 @@ class MaterialStateExample extends StatelessWidget {
     return Theme(
       data: themeData.copyWith(
         inputDecorationTheme: themeData.inputDecorationTheme.copyWith(
-          prefixIconColor: WidgetStateColor.resolveWith(
-            (Set<WidgetState> states) {
-              if (states.contains(WidgetState.error)) {
-                return Colors.red;
-              }
-              if (states.contains(WidgetState.focused)) {
-                return Colors.blue;
-              }
-              return Colors.grey;
+          prefixIconColor: WidgetStateColor.fromMap(
+            <WidgetStatesConstraint, Color>{
+              WidgetState.error:   Colors.red,
+              WidgetState.focused: Colors.blue,
+              WidgetState.any:     Colors.grey,
             },
           ),
         ),

examples/api/lib/material/list_tile/list_tile.3.dart

@@ -45,19 +45,13 @@ class _ListTileExampleState extends State<ListTileExample> {
               _selected = !_selected;
             });
           },
-          // This sets text color and icon color to red when list tile is disabled and
-          // green when list tile is selected, otherwise sets it to black.
-          iconColor: WidgetStateColor.resolveWith((Set<WidgetState> states) {
-            if (states.contains(WidgetState.disabled)) {
-              return Colors.red;
-            }
-            if (states.contains(WidgetState.selected)) {
-              return Colors.green;
-            }
-            return Colors.black;
+          iconColor: WidgetStateColor.fromMap(<WidgetStatesConstraint, Color>{
+            WidgetState.disabled: Colors.red,
+            WidgetState.selected: Colors.green,
+            WidgetState.any:      Colors.black,
           }),
-          // This sets text color and icon color to red when list tile is disabled and
-          // green when list tile is selected, otherwise sets it to black.
+          // The same can be achieved using the .resolveWith() constructor.
+          // The text color will be identical to the icon color above.
           textColor: WidgetStateColor.resolveWith((Set<WidgetState> states) {
             if (states.contains(WidgetState.disabled)) {
               return Colors.red;

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

@@ -37,32 +37,19 @@ class _SwitchExampleState extends State<SwitchExample> {
 
   @override
   Widget build(BuildContext context) {
-    final WidgetStateProperty<Color?> trackColor = WidgetStateProperty.resolveWith<Color?>(
-      (Set<WidgetState> states) {
-        // Track color when the switch is selected.
-        if (states.contains(WidgetState.selected)) {
-          return Colors.amber;
-        }
-        // Otherwise return null to set default track color
-        // for remaining states such as when the switch is
-        // hovered, focused, or disabled.
-        return null;
+    // This object sets amber as the track color when the switch is selected.
+    // Otherwise, it resolves to null and defers to values from the theme data.
+    const WidgetStateProperty<Color?> trackColor = WidgetStateProperty<Color?>.fromMap(
+      <WidgetStatesConstraint, Color>{
+        WidgetState.selected: Colors.amber,
       },
     );
-    final WidgetStateProperty<Color?> overlayColor = WidgetStateProperty.resolveWith<Color?>(
-      (Set<WidgetState> states) {
-        // Material color when switch is selected.
-        if (states.contains(WidgetState.selected)) {
-          return Colors.amber.withOpacity(0.54);
-        }
-        // Material color when switch is disabled.
-        if (states.contains(WidgetState.disabled)) {
-          return Colors.grey.shade400;
-        }
-        // Otherwise return null to set default material color
-        // for remaining states such as when the switch is
-        // hovered, or focused.
-        return null;
+    // This object sets the track color based on two WidgetState attributes.
+    // If neither state applies, it resolves to null.
+    final WidgetStateProperty<Color?> overlayColor = WidgetStateProperty<Color?>.fromMap(
+      <WidgetState, Color>{
+        WidgetState.selected: Colors.amber.withOpacity(0.54),
+        WidgetState.disabled: Colors.grey.shade400,
       },
     );
 

examples/api/lib/material/switch/switch.2.dart

@@ -36,12 +36,10 @@ class _SwitchExampleState extends State<SwitchExample> {
   bool light0 = true;
   bool light1 = true;
 
-  final WidgetStateProperty<Icon?> thumbIcon = WidgetStateProperty.resolveWith<Icon?>(
-    (Set<WidgetState> states) {
-      if (states.contains(WidgetState.selected)) {
-        return const Icon(Icons.check);
-      }
-      return const Icon(Icons.close);
+  static const WidgetStateProperty<Icon> thumbIcon = WidgetStateProperty<Icon>.fromMap(
+    <WidgetStatesConstraint, Icon>{
+      WidgetState.selected: Icon(Icons.check),
+      WidgetState.any:      Icon(Icons.close),
     },
   );
 

examples/api/lib/material/switch/switch.4.dart

@@ -120,14 +120,12 @@ class _SwitchThemeAdaptation extends Adaptation<SwitchThemeData> {
         return defaultValue;
       case TargetPlatform.iOS:
       case TargetPlatform.macOS:
-        return SwitchThemeData(
-          thumbColor: WidgetStateProperty.resolveWith<Color?>((Set<WidgetState> states) {
-            if (states.contains(WidgetState.selected)) {
-              return Colors.yellow;
-            }
-            return null; // Use the default.
+        return const SwitchThemeData(
+          thumbColor: WidgetStateProperty<Color?>.fromMap(<WidgetState, Color>{
+            WidgetState.selected: Colors.yellow,
+            // Resolves to null if not selected, deferring to default values.
           }),
-          trackColor: const WidgetStatePropertyAll<Color>(Colors.brown),
+          trackColor: WidgetStatePropertyAll<Color>(Colors.brown),
         );
     }
   }

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

@@ -66,30 +66,24 @@ class Home extends StatefulWidget {
 class _HomeState extends State<Home> {
   bool selected = false;
 
+  /// Sets the button's foreground and background colors.
+  /// If not selected, resolves to null and defers to default values.
+  static const ButtonStyle style = ButtonStyle(
+    foregroundColor: WidgetStateProperty<Color?>.fromMap(<WidgetState, Color>{
+      WidgetState.selected: Colors.white,
+    }),
+    backgroundColor: WidgetStateProperty<Color?>.fromMap(<WidgetState, Color>{
+      WidgetState.selected: Colors.indigo,
+    }),
+  );
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
       body: Center(
         child: SelectableButton(
           selected: selected,
-          style: ButtonStyle(
-            foregroundColor: WidgetStateProperty.resolveWith<Color?>(
-              (Set<WidgetState> states) {
-                if (states.contains(WidgetState.selected)) {
-                  return Colors.white;
-                }
-                return null; // defer to the defaults
-              },
-            ),
-            backgroundColor: WidgetStateProperty.resolveWith<Color?>(
-              (Set<WidgetState> states) {
-                if (states.contains(WidgetState.selected)) {
-                  return Colors.indigo;
-                }
-                return null; // defer to the defaults
-              },
-            ),
-          ),
+          style: style,
           onPressed: () {
             setState(() {
               selected = !selected;

examples/api/lib/widgets/focus_traversal/focus_traversal_group.0.dart

@@ -78,23 +78,6 @@ class _OrderedButtonState<T> extends State<OrderedButton<T>> {
       order = LexicalFocusOrder(widget.order.toString());
     }
 
-    Color? overlayColor(Set<WidgetState> states) {
-      if (states.contains(WidgetState.focused)) {
-        return Colors.red;
-      }
-      if (states.contains(WidgetState.hovered)) {
-        return Colors.blue;
-      }
-      return null; // defer to the default overlayColor
-    }
-
-    Color? foregroundColor(Set<WidgetState> states) {
-      if (states.contains(WidgetState.focused) || states.contains(WidgetState.hovered)) {
-        return Colors.white;
-      }
-      return null; // defer to the default foregroundColor
-    }
-
     return FocusTraversalOrder(
       order: order,
       child: Padding(
@@ -102,9 +85,24 @@ class _OrderedButtonState<T> extends State<OrderedButton<T>> {
         child: OutlinedButton(
           focusNode: focusNode,
           autofocus: widget.autofocus,
-          style: ButtonStyle(
-            overlayColor: WidgetStateProperty.resolveWith<Color?>(overlayColor),
-            foregroundColor: WidgetStateProperty.resolveWith<Color?>(foregroundColor),
+          style: const ButtonStyle(
+            overlayColor: WidgetStateProperty<Color?>.fromMap(
+              // If neither of these states is active, the property will
+              // resolve to null, deferring to the default overlay color.
+              <WidgetState, Color>{
+                WidgetState.focused: Colors.red,
+                WidgetState.hovered: Colors.blue,
+              },
+            ),
+            foregroundColor: WidgetStateProperty<Color?>.fromMap(
+              // "WidgetState.focused | WidgetState.hovered" could be used
+              // instead of separate map keys, but this setup allows setting
+              // the button style to a constant value for improved efficiency.
+              <WidgetState, Color>{
+                WidgetState.focused: Colors.white,
+                WidgetState.hovered: Colors.white,
+              },
+            ),
           ),
           onPressed: () => _handleOnPressed(),
           child: Text(widget.name),