Updated the ThemeData API example (#130954)

examples/api/lib/material/theme_data/theme_data.0.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+void main() {
+  runApp(const ThemeDataExampleApp());
+}
+
+// This app's theme specifies an overall ColorScheme as well as overrides
+// for the default configuration of FloatingActionButtons. To customize
+// the appearance of other components, add additional component specific
+// themes, rather than tweaking the color scheme.
+//
+// Creating an entire color scheme from a single seed color is a good
+// way to ensure a visually appealing color palette where the default
+// component colors have sufficient contrast for accessibility. Another
+// good way to create an app's color scheme is to use
+// ColorScheme.fromImageProvider.
+//
+// The color scheme reflects the platform's light or dark setting
+// which is retrieved with `MediaQuery.platformBrightnessOf`. The color
+// scheme's colors will be different for light and dark settings although
+// they'll all be related to the seed color in both cases.
+//
+// Color scheme colors have been used where component defaults have
+// been overidden so that the app will look good and remain accessible
+// in both light and dark modes.
+//
+// Text styles are derived from the theme's textTheme (not the obsolete
+// primaryTextTheme property) and then customized using copyWith.
+// Using the _on_ version of a color scheme color as the foreground,
+// as in `tertiary` and `onTertiary`, guarantees sufficient contrast
+// for readability/accessibility.
+
+class ThemeDataExampleApp extends StatelessWidget {
+  const ThemeDataExampleApp({ super.key });
+
+  @override
+  Widget build(BuildContext context) {
+    final ColorScheme colorScheme = ColorScheme.fromSeed(
+      brightness: MediaQuery.platformBrightnessOf(context),
+      seedColor: Colors.indigo,
+    );
+    return MaterialApp(
+      title: 'ThemeData Demo',
+      theme: ThemeData(
+        colorScheme: colorScheme,
+        floatingActionButtonTheme: FloatingActionButtonThemeData(
+          backgroundColor: colorScheme.tertiary,
+          foregroundColor: colorScheme.onTertiary,
+        ),
+      ),
+      home: const Home(),
+    );
+  }
+}
+
+class Home extends StatefulWidget {
+  const Home({ super.key });
+
+  @override
+  State<Home> createState() => _HomeState();
+}
+
+class _HomeState extends State<Home> {
+  int buttonPressCount = 0;
+
+  @override
+  Widget build(BuildContext context) {
+    final ThemeData theme = Theme.of(context);
+    final ColorScheme colorScheme = theme.colorScheme;
+    final double pointCount = 8 + (buttonPressCount % 6);
+
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Press the + Button'),
+      ),
+      // An AnimatedContainer makes the decoration changes entertaining.
+      body: AnimatedContainer(
+        duration: const Duration(milliseconds: 500),
+        margin: const EdgeInsets.all(32),
+        alignment: Alignment.center,
+        decoration: ShapeDecoration(
+          color: colorScheme.tertiaryContainer,
+          shape: StarBorder(
+            points: pointCount,
+            pointRounding: 0.4,
+            valleyRounding: 0.6,
+            side: BorderSide(
+              width: 9,
+              color: colorScheme.tertiary
+            ),
+          ),
+        ),
+        child: Text(
+          '${pointCount.toInt()} Points',
+          style: theme.textTheme.headlineMedium!.copyWith(
+            color: colorScheme.onPrimaryContainer,
+          ),
+        ),
+      ),
+      floatingActionButton: FloatingActionButton(
+        onPressed: () {
+          setState(() {
+            buttonPressCount += 1;
+          });
+        },
+        tooltip: "Change the shape's point count",
+        child: const Icon(Icons.add),
+      ),
+    );
+  }
+}

examples/api/test/material/theme_data/theme_data.0_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_api_samples/material/theme_data/theme_data.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+
+  testWidgets('ThemeData basics', (WidgetTester tester) async {
+    await tester.pumpWidget(const example.ThemeDataExampleApp());
+
+    final ColorScheme colorScheme = ColorScheme.fromSeed(
+      seedColor: Colors.indigo,
+    );
+
+    final Material fabMaterial = tester.widget<Material>(
+      find.descendant(of: find.byType(FloatingActionButton), matching: find.byType(Material)),
+    );
+    expect(fabMaterial.color, colorScheme.tertiary);
+
+    final RichText iconRichText = tester.widget<RichText>(
+      find.descendant(of: find.byIcon(Icons.add), matching: find.byType(RichText)),
+    );
+    expect(iconRichText.text.style!.color, colorScheme.onTertiary);
+
+    expect(find.text('8 Points'), isNotNull);
+    await tester.tap(find.byType(FloatingActionButton));
+    await tester.pumpAndSettle();
+    expect(find.text('9 Points'), isNotNull);
+    await tester.tap(find.byType(FloatingActionButton));
+    await tester.pumpAndSettle();
+    expect(find.text('10 Points'), isNotNull);
+  });
+}

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

@@ -179,68 +179,15 @@ enum MaterialTapTargetSize {
 /// for the subtree that appears below the new [Theme], or insert a widget
 /// that creates a new BuildContext, like [Builder].
 ///
-/// {@tool snippet}
-/// In this example, the [Container] widget uses [Theme.of] to retrieve the
-/// primary color from the theme's [colorScheme] to draw an amber square.
-/// The [Builder] widget separates the parent theme's [BuildContext] from the
-/// child's [BuildContext].
-///
-/// ![](https://flutter.github.io/assets-for-api-docs/assets/material/theme_data.png)
-///
-/// ```dart
-/// Theme(
-///   data: ThemeData.from(
-///     colorScheme: ColorScheme.fromSwatch(primarySwatch: Colors.amber),
-///   ),
-///   child: Builder(
-///     builder: (BuildContext context) {
-///       return Container(
-///         width: 100,
-///         height: 100,
-///         color: Theme.of(context).colorScheme.primary,
-///       );
-///     },
-///   ),
-/// )
-/// ```
-/// {@end-tool}
-///
-/// {@tool snippet}
-///
-/// This sample creates a [MaterialApp] with a [Theme] whose
-/// [ColorScheme] is based on [Colors.blue], but with the color
-/// scheme's [ColorScheme.secondary] color overridden to be green. The
-/// [AppBar] widget uses the color scheme's [ColorScheme.primary] as
-/// its default background color and the [FloatingActionButton] widget
-/// uses the color scheme's [ColorScheme.secondary] for its default
-/// background. By default, the [Text] widget uses
-/// [TextTheme.bodyMedium], and the color of that [TextStyle] has been
-/// changed to purple.
-///
-/// ![](https://flutter.github.io/assets-for-api-docs/assets/material/material_app_theme_data.png)
+/// {@tool dartpad}
+/// This example demonstrates how a typical [MaterialApp] specifies
+/// and uses a custom [Theme]. The theme's [ColorScheme] is based on a
+/// single "seed" color and configures itself to match the platform's
+/// current light or dark color configuration. The theme overrides the
+/// default configuration of [FloatingActionButton] to show how to
+/// customize the appearance a class of components.
 ///
-/// ```dart
-/// MaterialApp(
-///   theme: ThemeData(
-///     colorScheme: ColorScheme.fromSwatch().copyWith(
-///       secondary: Colors.green,
-///     ),
-///     textTheme: const TextTheme(bodyMedium: TextStyle(color: Colors.purple)),
-///   ),
-///   home: Scaffold(
-///     appBar: AppBar(
-///       title: const Text('ThemeData Demo'),
-///     ),
-///     floatingActionButton: FloatingActionButton(
-///       child: const Icon(Icons.add),
-///       onPressed: () {},
-///     ),
-///     body: const Center(
-///       child: Text('Button pressed 0 times'),
-///     ),
-///   ),
-/// )
-/// ```
+/// ** See code in examples/api/lib/material/theme_data/theme_data.0.dart **
 /// {@end-tool}
 ///
 /// See <https://material.io/design/color/> for