Migrate AppBar to Material 3 (#101884)

dev/tools/gen_defaults/bin/gen_defaults.dart

@@ -17,6 +17,7 @@
 import 'dart:convert';
 import 'dart:io';
 
+import 'package:gen_defaults/app_bar_template.dart';
 import 'package:gen_defaults/button_template.dart';
 import 'package:gen_defaults/card_template.dart';
 import 'package:gen_defaults/dialog_template.dart';
@@ -78,6 +79,7 @@ Future<void> main(List<String> args) async {
   tokens['colorsLight'] = _readTokenFile('color_light.json');
   tokens['colorsDark'] = _readTokenFile('color_dark.json');
 
+  AppBarTemplate('$materialLib/app_bar.dart', tokens).updateFile();
   ButtonTemplate('md.comp.elevated-button', '$materialLib/elevated_button.dart', tokens).updateFile();
   ButtonTemplate('md.comp.outlined-button', '$materialLib/outlined_button.dart', tokens).updateFile();
   ButtonTemplate('md.comp.text-button', '$materialLib/text_button.dart', tokens).updateFile();

dev/tools/gen_defaults/lib/app_bar_template.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 'template.dart';
+
+class AppBarTemplate extends TokenTemplate {
+  const AppBarTemplate(super.fileName, super.tokens)
+    : super(
+      colorSchemePrefix: '_colors.',
+      textThemePrefix: '_textTheme.',
+    );
+
+  @override
+  String generate() => '''
+// Generated version ${tokens["version"]}
+class _TokenDefaultsM3 extends AppBarTheme {
+  _TokenDefaultsM3(this.context)
+    : super(
+      elevation: ${elevation('md.comp.top-app-bar.small.container')},
+      scrolledUnderElevation: ${elevation('md.comp.top-app-bar.small.on-scroll.container')},
+      titleSpacing: NavigationToolbar.kMiddleSpacing,
+      toolbarHeight: ${tokens['md.comp.top-app-bar.small.container.height']},
+    );
+
+  final BuildContext context;
+  late final ThemeData _theme = Theme.of(context);
+  late final ColorScheme _colors = _theme.colorScheme;
+  late final TextTheme _textTheme = _theme.textTheme;
+
+  @override
+  Color? get backgroundColor => ${componentColor('md.comp.top-app-bar.small.container')};
+
+  @override
+  Color? get foregroundColor => ${color('md.comp.top-app-bar.small.headline.color')};
+
+  @override
+  Color? get surfaceTintColor => ${componentColor('md.comp.top-app-bar.small.container.surface-tint-layer')};
+
+  @override
+  IconThemeData? get iconTheme => IconThemeData(
+    color: ${componentColor('md.comp.top-app-bar.small.leading-icon')},
+    size: ${tokens['md.comp.top-app-bar.small.leading-icon.size']},
+  );
+
+  @override
+  IconThemeData? get actionsIconTheme => IconThemeData(
+    color: ${componentColor('md.comp.top-app-bar.small.trailing-icon')},
+    size: ${tokens['md.comp.top-app-bar.small.trailing-icon.size']},
+  );
+
+  @override
+  TextStyle? get toolbarTextStyle => _textTheme.bodyText2;
+
+  @override
+  TextStyle? get titleTextStyle => ${textStyle('md.comp.top-app-bar.small.headline')};
+}''';
+}

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

@@ -37,7 +37,9 @@ class AppBarTheme with Diagnosticable {
     Color? backgroundColor,
     this.foregroundColor,
     this.elevation,
+    this.scrolledUnderElevation,
     this.shadowColor,
+    this.surfaceTintColor,
     this.shape,
     this.iconTheme,
     this.actionsIconTheme,
@@ -121,10 +123,18 @@ class AppBarTheme with Diagnosticable {
   /// descendant [AppBar] widgets.
   final double? elevation;
 
+  /// Overrides the default value of [AppBar.scrolledUnderElevation] in all
+  /// descendant [AppBar] widgets.
+  final double? scrolledUnderElevation;
+
   /// Overrides the default value for [AppBar.shadowColor] in all
   /// descendant widgets.
   final Color? shadowColor;
 
+  /// Overrides the default value for [AppBar.surfaceTintColor] in all
+  /// descendant widgets.
+  final Color? surfaceTintColor;
+
   /// Overrides the default value for [AppBar.shape] in all
   /// descendant widgets.
   final ShapeBorder? shape;
@@ -237,7 +247,9 @@ class AppBarTheme with Diagnosticable {
     Color? backgroundColor,
     Color? foregroundColor,
     double? elevation,
+    double? scrolledUnderElevation,
     Color? shadowColor,
+    Color? surfaceTintColor,
     ShapeBorder? shape,
     IconThemeData? iconTheme,
     @Deprecated(
@@ -266,7 +278,9 @@ class AppBarTheme with Diagnosticable {
       backgroundColor: backgroundColor ?? color ?? this.backgroundColor,
       foregroundColor: foregroundColor ?? this.foregroundColor,
       elevation: elevation ?? this.elevation,
+      scrolledUnderElevation: scrolledUnderElevation ?? this.scrolledUnderElevation,
       shadowColor: shadowColor ?? this.shadowColor,
+      surfaceTintColor: surfaceTintColor ?? this.surfaceTintColor,
       shape: shape ?? this.shape,
       iconTheme: iconTheme ?? this.iconTheme,
       actionsIconTheme: actionsIconTheme ?? this.actionsIconTheme,
@@ -298,7 +312,9 @@ class AppBarTheme with Diagnosticable {
       backgroundColor: Color.lerp(a?.backgroundColor, b?.backgroundColor, t),
       foregroundColor: Color.lerp(a?.foregroundColor, b?.foregroundColor, t),
       elevation: lerpDouble(a?.elevation, b?.elevation, t),
+      scrolledUnderElevation: lerpDouble(a?.scrolledUnderElevation, b?.scrolledUnderElevation, t),
       shadowColor: Color.lerp(a?.shadowColor, b?.shadowColor, t),
+      surfaceTintColor: Color.lerp(a?.surfaceTintColor, b?.surfaceTintColor, t),
       shape: ShapeBorder.lerp(a?.shape, b?.shape, t),
       iconTheme: IconThemeData.lerp(a?.iconTheme, b?.iconTheme, t),
       actionsIconTheme: IconThemeData.lerp(a?.actionsIconTheme, b?.actionsIconTheme, t),
@@ -319,7 +335,9 @@ class AppBarTheme with Diagnosticable {
     backgroundColor,
     foregroundColor,
     elevation,
+    scrolledUnderElevation,
     shadowColor,
+    surfaceTintColor,
     shape,
     iconTheme,
     actionsIconTheme,
@@ -344,7 +362,9 @@ class AppBarTheme with Diagnosticable {
         && other.backgroundColor == backgroundColor
         && other.foregroundColor == foregroundColor
         && other.elevation == elevation
+        && other.scrolledUnderElevation == scrolledUnderElevation
         && other.shadowColor == shadowColor
+        && other.surfaceTintColor == surfaceTintColor
         && other.shape == shape
         && other.iconTheme == iconTheme
         && other.actionsIconTheme == actionsIconTheme
@@ -365,7 +385,9 @@ class AppBarTheme with Diagnosticable {
     properties.add(ColorProperty('backgroundColor', backgroundColor, defaultValue: null));
     properties.add(ColorProperty('foregroundColor', foregroundColor, defaultValue: null));
     properties.add(DiagnosticsProperty<double>('elevation', elevation, defaultValue: null));
+    properties.add(DiagnosticsProperty<double>('scrolledUnderElevation', scrolledUnderElevation, defaultValue: null));
     properties.add(ColorProperty('shadowColor', shadowColor, defaultValue: null));
+    properties.add(ColorProperty('surfaceTintColor', surfaceTintColor, defaultValue: null));
     properties.add(DiagnosticsProperty<ShapeBorder>('shape', shape, defaultValue: null));
     properties.add(DiagnosticsProperty<IconThemeData>('iconTheme', iconTheme, defaultValue: null));
     properties.add(DiagnosticsProperty<IconThemeData>('actionsIconTheme', actionsIconTheme, defaultValue: null));

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

@@ -400,6 +400,9 @@ class _MaterialState extends State<Material> with TickerProviderStateMixin {
   Widget build(BuildContext context) {
     final ThemeData theme = Theme.of(context);
     final Color? backgroundColor = _getBackgroundColor(context);
+    final Color? modelShadowColor = widget.shadowColor ?? (theme.useMaterial3 ? null : theme.shadowColor);
+    // If no shadow color is specified, use 0 for elevation in the model so a drop shadow won't be painted.
+    final double modelElevation = modelShadowColor != null ? widget.elevation : 0;
     assert(
       backgroundColor != null || widget.type == MaterialType.transparency,
       'If Material type is not MaterialType.transparency, a color must '
@@ -449,9 +452,9 @@ class _MaterialState extends State<Material> with TickerProviderStateMixin {
         duration: widget.animationDuration,
         shape: BoxShape.rectangle,
         clipBehavior: widget.clipBehavior,
-        elevation: widget.elevation,
+        elevation: modelElevation,
         color: color,
-        shadowColor: widget.shadowColor ?? (theme.useMaterial3 ? const Color(0x00000000) : theme.shadowColor),
+        shadowColor: modelShadowColor ?? const Color(0x00000000),
         animateColor: false,
         child: contents,
       );
@@ -476,7 +479,7 @@ class _MaterialState extends State<Material> with TickerProviderStateMixin {
       clipBehavior: widget.clipBehavior,
       elevation: widget.elevation,
       color: backgroundColor!,
-      shadowColor: widget.shadowColor ?? (theme.useMaterial3 ? const Color(0x00000000) : theme.shadowColor),
+      shadowColor: modelShadowColor,
       surfaceTintColor: widget.surfaceTintColor,
       child: contents,
     );
@@ -742,8 +745,7 @@ class _MaterialInterior extends ImplicitlyAnimatedWidget {
        assert(shape != null),
        assert(clipBehavior != null),
        assert(elevation != null && elevation >= 0.0),
-       assert(color != null),
-       assert(shadowColor != null);
+       assert(color != null);
 
   /// The widget below this widget in the tree.
   ///
@@ -777,7 +779,7 @@ class _MaterialInterior extends ImplicitlyAnimatedWidget {
   final Color color;
 
   /// The target shadow color.
-  final Color shadowColor;
+  final Color? shadowColor;
 
   /// The target surface tint color.
   final Color? surfaceTintColor;
@@ -808,11 +810,13 @@ class _MaterialInteriorState extends AnimatedWidgetBaseState<_MaterialInterior>
       widget.elevation,
       (dynamic value) => Tween<double>(begin: value as double),
     ) as Tween<double>?;
-    _shadowColor = visitor(
-      _shadowColor,
-      widget.shadowColor,
-      (dynamic value) => ColorTween(begin: value as Color),
-    ) as ColorTween?;
+    _shadowColor =  widget.shadowColor != null
+      ? visitor(
+          _shadowColor,
+          widget.shadowColor,
+          (dynamic value) => ColorTween(begin: value as Color),
+        ) as ColorTween?
+      : null;
     _surfaceTintColor = widget.surfaceTintColor != null
       ? visitor(
           _surfaceTintColor,
@@ -834,15 +838,18 @@ class _MaterialInteriorState extends AnimatedWidgetBaseState<_MaterialInterior>
     final Color color = Theme.of(context).useMaterial3
       ? ElevationOverlay.applySurfaceTint(widget.color, _surfaceTintColor?.evaluate(animation), elevation)
       : ElevationOverlay.applyOverlay(context, widget.color, elevation);
+    // If no shadow color is specified, use 0 for elevation in the model so a drop shadow won't be painted.
+    final double modelElevation = widget.shadowColor != null ? elevation : 0;
+    final Color shadowColor = _shadowColor?.evaluate(animation) ?? const Color(0x00000000);
     return PhysicalShape(
       clipper: ShapeBorderClipper(
         shape: shape,
         textDirection: Directionality.maybeOf(context),
       ),
       clipBehavior: widget.clipBehavior,
-      elevation: elevation,
+      elevation: modelElevation,
       color: color,
-      shadowColor: _shadowColor!.evaluate(animation)!,
+      shadowColor: shadowColor,
       child: _ShapeBorderPaint(
         shape: shape,
         borderOnForeground: widget.borderOnForeground,

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

@@ -1203,6 +1203,7 @@ class ThemeData with Diagnosticable {
   /// Components that have been migrated to Material 3 are:
   ///
   ///   * [AlertDialog]
+  ///   * [AppBar]
   ///   * [Card]
   ///   * [Dialog]
   ///   * [ElevatedButton]

packages/flutter/test/material/app_bar_test.dart

@@ -954,6 +954,8 @@ void main() {
   });
 
   testWidgets('AppBar uses the specified elevation or defaults to 4.0', (WidgetTester tester) async {
+    final bool useMaterial3 = ThemeData().useMaterial3;
+
     Widget buildAppBar([double? elevation]) {
       return MaterialApp(
         home: Scaffold(
@@ -967,15 +969,48 @@ void main() {
       matching: find.byType(Material),
     ));
 
-    // Default elevation should be _AppBarState._defaultElevation = 4.0
+    // Default elevation should be used for the material.
     await tester.pumpWidget(buildAppBar());
-    expect(getMaterial().elevation, 4.0);
+    expect(getMaterial().elevation, useMaterial3 ? 0 : 4);
 
     // AppBar should use the specified elevation.
     await tester.pumpWidget(buildAppBar(8.0));
     expect(getMaterial().elevation, 8.0);
   });
 
+  testWidgets('scrolledUnderElevation', (WidgetTester tester) async {
+    Widget buildAppBar({double? elevation, double? scrolledUnderElevation}) {
+      return MaterialApp(
+        home: Scaffold(
+          appBar: AppBar(
+            title: const Text('Title'),
+            elevation: elevation,
+            scrolledUnderElevation: scrolledUnderElevation,
+          ),
+          body: ListView.builder(
+            itemCount: 100,
+            itemBuilder: (BuildContext context, int index) => ListTile(title: Text('Item $index')),
+          ),
+        ),
+      );
+    }
+
+    Material getMaterial() => tester.widget<Material>(find.descendant(
+      of: find.byType(AppBar),
+      matching: find.byType(Material),
+    ));
+
+    await tester.pumpWidget(buildAppBar(elevation: 2, scrolledUnderElevation: 10));
+    // Starts with the base elevation.
+    expect(getMaterial().elevation, 2);
+
+    await tester.fling(find.text('Item 2'), const Offset(0.0, -600.0), 2000.0);
+    await tester.pumpAndSettle();
+
+    // After scrolling it should be the scrolledUnderElevation.
+    expect(getMaterial().elevation, 10);
+  });
+
   group('SliverAppBar elevation', () {
     Widget buildSliverAppBar(bool forceElevated, {double? elevation, double? themeElevation}) {
       return MaterialApp(
@@ -996,15 +1031,16 @@ void main() {
       // Regression test for https://github.com/flutter/flutter/issues/59158.
       AppBar getAppBar() => tester.widget<AppBar>(find.byType(AppBar));
       Material getMaterial() => tester.widget<Material>(find.byType(Material));
+      final bool useMaterial3 = ThemeData().useMaterial3;
 
       // When forceElevated is off, SliverAppBar should not be elevated.
       await tester.pumpWidget(buildSliverAppBar(false));
       expect(getMaterial().elevation, 0.0);
 
-      // Default elevation should be _AppBarState._defaultElevation = 4.0, and
+      // Default elevation should be used by the material, but
       // the AppBar's elevation should not be specified by SliverAppBar.
       await tester.pumpWidget(buildSliverAppBar(true));
-      expect(getMaterial().elevation, 4.0);
+      expect(getMaterial().elevation, useMaterial3 ? 0.0 : 4.0);
       expect(getAppBar().elevation, null);
 
       // SliverAppBar should use the specified elevation.
@@ -1312,6 +1348,8 @@ void main() {
     final Key key = UniqueKey();
     await tester.pumpWidget(
       MaterialApp(
+        // Test was designed against InkSplash so need to make sure that is used.
+        theme: ThemeData(splashFactory: InkSplash.splashFactory),
         home: Center(
           child: AppBar(
             title: const Text('Abc'),
@@ -2005,44 +2043,55 @@ void main() {
     ));
   });
 
-  testWidgets('AppBar draws a light system bar for a light theme with a dark background', (WidgetTester tester) async {
-    final ThemeData lightTheme = ThemeData(primarySwatch: Colors.deepOrange);
-    await tester.pumpWidget(MaterialApp(
-      theme: lightTheme,
-      home: Scaffold(
-        appBar: AppBar(
-          title: const Text('test'),
+  testWidgets('Default system bar brightness based on AppBar background color brightness.', (WidgetTester tester) async {
+    Widget buildAppBar(ThemeData theme) {
+      return MaterialApp(
+        theme: theme,
+        home: Scaffold(
+          appBar: AppBar(title: const Text('Title')),
         ),
-      ),
-    ));
-
-    expect(lightTheme.primaryColorBrightness, Brightness.dark);
-    expect(lightTheme.colorScheme.brightness, Brightness.light);
-    expect(SystemChrome.latestStyle, const SystemUiOverlayStyle(
-      statusBarBrightness: Brightness.dark,
-      statusBarIconBrightness: Brightness.light,
-    ));
-  });
+      );
+    }
 
-  testWidgets('AppBar draws a dark system bar for a dark theme with a light background', (WidgetTester tester) async {
-    final ThemeData darkTheme = ThemeData(brightness: Brightness.dark, cardColor: Colors.white);
-    await tester.pumpWidget(
-      MaterialApp(
-        theme: darkTheme,
-        home: Scaffold(
-          appBar: AppBar(
-            title: const Text('test'),
-          ),
+    // Using a light theme.
+    {
+      await tester.pumpWidget(buildAppBar(ThemeData.from(colorScheme: const ColorScheme.light())));
+      final Material appBarMaterial = tester.widget<Material>(
+        find.descendant(
+          of: find.byType(AppBar),
+          matching: find.byType(Material),
         ),
-      ),
-    );
+      );
+      final Brightness appBarBrightness = ThemeData.estimateBrightnessForColor(appBarMaterial.color!);
+      final Brightness onAppBarBrightness = appBarBrightness == Brightness.light
+        ? Brightness.dark
+        : Brightness.light;
+
+      expect(SystemChrome.latestStyle, SystemUiOverlayStyle(
+        statusBarBrightness: appBarBrightness,
+        statusBarIconBrightness: onAppBarBrightness,
+      ));
+    }
 
-    expect(darkTheme.primaryColorBrightness, Brightness.dark);
-    expect(darkTheme.colorScheme.brightness, Brightness.dark);
-    expect(SystemChrome.latestStyle, const SystemUiOverlayStyle(
-      statusBarBrightness: Brightness.light,
-      statusBarIconBrightness: Brightness.dark,
-    ));
+    // Using a dark theme.
+    {
+      await tester.pumpWidget(buildAppBar(ThemeData.from(colorScheme: const ColorScheme.dark())));
+      final Material appBarMaterial = tester.widget<Material>(
+        find.descendant(
+          of: find.byType(AppBar),
+          matching: find.byType(Material),
+        ),
+      );
+      final Brightness appBarBrightness = ThemeData.estimateBrightnessForColor(appBarMaterial.color!);
+      final Brightness onAppBarBrightness = appBarBrightness == Brightness.light
+          ? Brightness.dark
+          : Brightness.light;
+
+      expect(SystemChrome.latestStyle, SystemUiOverlayStyle(
+        statusBarBrightness: appBarBrightness,
+        statusBarIconBrightness: onAppBarBrightness,
+      ));
+    }
   });
 
   testWidgets('Changing SliverAppBar snap from true to false', (WidgetTester tester) async {
@@ -2207,6 +2256,8 @@ void main() {
 
     Widget buildFrame() {
       return MaterialApp(
+        // Test designed against 2014 font sizes.
+        theme: ThemeData(textTheme: Typography.englishLike2014),
         home: Builder(
           builder: (BuildContext context) {
             return MediaQuery(
@@ -2245,6 +2296,8 @@ void main() {
 
     Widget buildFrame() {
       return MaterialApp(
+        // Test designed against 2014 font sizes.
+        theme: ThemeData(textTheme: Typography.englishLike2014),
         home: Builder(
           builder: (BuildContext context) {
             return Directionality(
@@ -2536,6 +2589,7 @@ void main() {
     await tester.pumpWidget(
       MaterialApp(
         theme: ThemeData.light().copyWith(
+          useMaterial3: false,
           appBarTheme: const AppBarTheme(
             backwardsCompatibility: false,
           ),