add navigation bar component (#83047)

packages/flutter/lib/material.dart

@@ -99,6 +99,8 @@ export 'src/material/material_localizations.dart';
 export 'src/material/material_state.dart';
 export 'src/material/material_state_mixin.dart';
 export 'src/material/mergeable_material.dart';
+export 'src/material/navigation_bar.dart';
+export 'src/material/navigation_bar_theme.dart';
 export 'src/material/navigation_rail.dart';
 export 'src/material/navigation_rail_theme.dart';
 export 'src/material/no_splash.dart';

packages/flutter/lib/src/material/navigation_bar_theme.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 'dart:ui' show lerpDouble;
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter/widgets.dart';
+
+import 'material_state.dart';
+import 'navigation_bar.dart';
+import 'theme.dart';
+
+/// Defines default property values for descendant [NavigationBar]
+/// widgets.
+///
+/// Descendant widgets obtain the current [NavigationBarThemeData] object
+/// using `NavigationBarTheme.of(context)`. Instances of
+/// [NavigationBarThemeData] can be customized with
+/// [NavigationBarThemeData.copyWith].
+///
+/// Typically a [NavigationBarThemeData] is specified as part of the
+/// overall [Theme] with [ThemeData.navigationBarTheme]. Alternatively, a
+/// [NavigationBarTheme] inherited widget can be used to theme [NavigationBar]s
+/// in a subtree of widgets.
+///
+/// All [NavigationBarThemeData] properties are `null` by default.
+/// When null, the [NavigationBar] will provide its own defaults based on the
+/// overall [Theme]'s textTheme and colorScheme. See the individual
+/// [NavigationBar] properties for details.
+///
+/// See also:
+///
+///  * [ThemeData], which describes the overall theme information for the
+///    application.
+@immutable
+class NavigationBarThemeData with Diagnosticable {
+  /// Creates a theme that can be used for [ThemeData.navigationBarTheme] and
+  /// [NavigationBarTheme].
+  const NavigationBarThemeData({
+    this.height,
+    this.backgroundColor,
+    this.indicatorColor,
+    this.labelTextStyle,
+    this.iconTheme,
+    this.labelBehavior,
+  });
+
+  /// Overrides the default value of [NavigationBar.height].
+  final double? height;
+
+  /// Overrides the default value of [NavigationBar.backgroundColor].
+  final Color? backgroundColor;
+
+  /// Overrides the default value of [NavigationBar]'s selection indicator.
+  final Color? indicatorColor;
+
+  /// The style to merge with the default text style for
+  /// [NavigationDestination] labels.
+  ///
+  /// You can use this to specify a different style when the label is selected.
+  final MaterialStateProperty<TextStyle?>? labelTextStyle;
+
+  /// The theme to merge with the default icon theme for
+  /// [NavigationDestination] icons.
+  ///
+  /// You can use this to specify a different icon theme when the icon is
+  /// selected.
+  final MaterialStateProperty<IconThemeData?>? iconTheme;
+
+  /// Overrides the default value of [NavigationBar.labelBehavior].
+  final NavigationDestinationLabelBehavior? labelBehavior;
+
+  /// Creates a copy of this object with the given fields replaced with the
+  /// new values.
+  NavigationBarThemeData copyWith({
+    double? height,
+    Color? backgroundColor,
+    Color? indicatorColor,
+    MaterialStateProperty<TextStyle?>? labelTextStyle,
+    MaterialStateProperty<IconThemeData?>? iconTheme,
+    NavigationDestinationLabelBehavior? labelBehavior,
+  }) {
+    return NavigationBarThemeData(
+      height: height ?? this.height,
+      backgroundColor: backgroundColor ?? this.backgroundColor,
+      indicatorColor: indicatorColor ?? this.indicatorColor,
+      labelTextStyle: labelTextStyle ?? this.labelTextStyle,
+      iconTheme: iconTheme ?? this.iconTheme,
+      labelBehavior: labelBehavior ?? this.labelBehavior,
+    );
+  }
+
+  /// Linearly interpolate between two navigation rail themes.
+  ///
+  /// If both arguments are null then null is returned.
+  ///
+  /// {@macro dart.ui.shadow.lerp}
+  static NavigationBarThemeData? lerp(NavigationBarThemeData? a, NavigationBarThemeData? b, double t) {
+    assert(t != null);
+    if (a == null && b == null)
+      return null;
+    return NavigationBarThemeData(
+      height: lerpDouble(a?.height, b?.height, t),
+      backgroundColor: Color.lerp(a?.backgroundColor, b?.backgroundColor, t),
+      indicatorColor: Color.lerp(a?.indicatorColor, b?.indicatorColor, t),
+      labelTextStyle: _lerpProperties<TextStyle?>(a?.labelTextStyle, b?.labelTextStyle, t, TextStyle.lerp),
+      iconTheme: _lerpProperties<IconThemeData?>(a?.iconTheme, b?.iconTheme, t, IconThemeData.lerp),
+      labelBehavior: t < 0.5 ? a?.labelBehavior : b?.labelBehavior,
+    );
+  }
+
+  @override
+  int get hashCode {
+    return hashValues(
+      height,
+      backgroundColor,
+      indicatorColor,
+      labelTextStyle,
+      iconTheme,
+      labelBehavior,
+    );
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (identical(this, other))
+      return true;
+    if (other.runtimeType != runtimeType)
+      return false;
+    return other is NavigationBarThemeData
+        && other.height == height
+        && other.backgroundColor == backgroundColor
+        && other.indicatorColor == indicatorColor
+        && other.labelTextStyle == labelTextStyle
+        && other.iconTheme == iconTheme
+        && other.labelBehavior == labelBehavior;
+  }
+
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+    super.debugFillProperties(properties);
+    properties.add(DoubleProperty('height', height, defaultValue: null));
+    properties.add(ColorProperty('backgroundColor', backgroundColor, defaultValue: null));
+    properties.add(ColorProperty('indicatorColor', indicatorColor, defaultValue: null));
+    properties.add(DiagnosticsProperty<MaterialStateProperty<TextStyle?>>('labelTextStyle', labelTextStyle, defaultValue: null));
+    properties.add(DiagnosticsProperty<MaterialStateProperty<IconThemeData?>>('iconTheme', iconTheme, defaultValue: null));
+    properties.add(DiagnosticsProperty<NavigationDestinationLabelBehavior>('labelBehavior', labelBehavior, defaultValue: null));
+  }
+
+  static MaterialStateProperty<T>? _lerpProperties<T>(
+    MaterialStateProperty<T>? a,
+    MaterialStateProperty<T>? b,
+    double t,
+    T Function(T?, T?, double) lerpFunction,
+  ) {
+    // Avoid creating a _LerpProperties object for a common case.
+    if (a == null && b == null)
+      return null;
+    return _LerpProperties<T>(a, b, t, lerpFunction);
+  }
+}
+
+class _LerpProperties<T> implements MaterialStateProperty<T> {
+  const _LerpProperties(this.a, this.b, this.t, this.lerpFunction);
+
+  final MaterialStateProperty<T>? a;
+  final MaterialStateProperty<T>? b;
+  final double t;
+  final T Function(T?, T?, double) lerpFunction;
+
+  @override
+  T resolve(Set<MaterialState> states) {
+    final T? resolvedA = a?.resolve(states);
+    final T? resolvedB = b?.resolve(states);
+    return lerpFunction(resolvedA, resolvedB, t);
+  }
+}
+
+/// An inherited widget that defines visual properties for [NavigationBar]s and
+/// [NavigationDestination]s in this widget's subtree.
+///
+/// Values specified here are used for [NavigationBar] properties that are not
+/// given an explicit non-null value.
+///
+/// See also:
+///
+///  * [ThemeData.navigationBarTheme], which describes the
+///    [NavigationBarThemeData] in the overall theme for the application.
+class NavigationBarTheme extends InheritedTheme {
+  /// Creates a navigation rail theme that controls the
+  /// [NavigationBarThemeData] properties for a [NavigationBar].
+  ///
+  /// The data argument must not be null.
+  const NavigationBarTheme({
+    Key? key,
+    required this.data,
+    required Widget child,
+  }) : assert(data != null), super(key: key, child: child);
+
+  /// Specifies the background color, label text style, icon theme, and label
+  /// type values for descendant [NavigationBar] widgets.
+  final NavigationBarThemeData data;
+
+  /// The closest instance of this class that encloses the given context.
+  ///
+  /// If there is no enclosing [NavigationBarTheme] widget, then
+  /// [ThemeData.navigationBarTheme] is used.
+  ///
+  /// Typical usage is as follows:
+  ///
+  /// ```dart
+  /// NavigationBarTheme theme = NavigationBarTheme.of(context);
+  /// ```
+  static NavigationBarThemeData of(BuildContext context) {
+    final NavigationBarTheme? navigationBarTheme = context.dependOnInheritedWidgetOfExactType<NavigationBarTheme>();
+    return navigationBarTheme?.data ?? Theme.of(context).navigationBarTheme;
+  }
+
+  @override
+  Widget wrap(BuildContext context, Widget child) {
+    return NavigationBarTheme(data: data, child: child);
+  }
+
+  @override
+  bool updateShouldNotify(NavigationBarTheme oldWidget) => data != oldWidget.data;
+}

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

@@ -28,6 +28,7 @@ import 'floating_action_button_theme.dart';
 import 'ink_splash.dart';
 import 'ink_well.dart' show InteractiveInkFeatureFactory;
 import 'input_decorator.dart';
+import 'navigation_bar_theme.dart';
 import 'navigation_rail_theme.dart';
 import 'outlined_button_theme.dart';
 import 'page_transitions_theme.dart';
@@ -317,6 +318,7 @@ class ThemeData with Diagnosticable {
     ColorScheme? colorScheme,
     DialogTheme? dialogTheme,
     FloatingActionButtonThemeData? floatingActionButtonTheme,
+    NavigationBarThemeData? navigationBarTheme,
     NavigationRailThemeData? navigationRailTheme,
     Typography? typography,
     NoDefaultCupertinoThemeData? cupertinoOverrideTheme,
@@ -462,6 +464,7 @@ class ThemeData with Diagnosticable {
     );
     dialogTheme ??= const DialogTheme();
     floatingActionButtonTheme ??= const FloatingActionButtonThemeData();
+    navigationBarTheme ??= const NavigationBarThemeData();
     navigationRailTheme ??= const NavigationRailThemeData();
     cupertinoOverrideTheme = cupertinoOverrideTheme?.noDefault();
     snackBarTheme ??= const SnackBarThemeData();
@@ -543,6 +546,7 @@ class ThemeData with Diagnosticable {
       colorScheme: colorScheme,
       dialogTheme: dialogTheme,
       floatingActionButtonTheme: floatingActionButtonTheme,
+      navigationBarTheme: navigationBarTheme,
       navigationRailTheme: navigationRailTheme,
       typography: typography,
       cupertinoOverrideTheme: cupertinoOverrideTheme,
@@ -677,6 +681,7 @@ class ThemeData with Diagnosticable {
     required this.colorScheme,
     required this.dialogTheme,
     required this.floatingActionButtonTheme,
+    required this.navigationBarTheme,
     required this.navigationRailTheme,
     required this.typography,
     required this.cupertinoOverrideTheme,
@@ -763,6 +768,7 @@ class ThemeData with Diagnosticable {
        assert(colorScheme != null),
        assert(dialogTheme != null),
        assert(floatingActionButtonTheme != null),
+       assert(navigationBarTheme != null),
        assert(navigationRailTheme != null),
        assert(typography != null),
        assert(snackBarTheme != null),
@@ -1269,6 +1275,10 @@ class ThemeData with Diagnosticable {
   /// [FloatingActionButton].
   final FloatingActionButtonThemeData floatingActionButtonTheme;
 
+  /// A theme for customizing the background color, text style, and icon themes
+  /// of a [NavigationBar].
+  final NavigationBarThemeData navigationBarTheme;
+
   /// A theme for customizing the background color, elevation, text style, and
   /// icon themes of a [NavigationRail].
   final NavigationRailThemeData navigationRailTheme;
@@ -1485,6 +1495,7 @@ class ThemeData with Diagnosticable {
     ColorScheme? colorScheme,
     DialogTheme? dialogTheme,
     FloatingActionButtonThemeData? floatingActionButtonTheme,
+    NavigationBarThemeData? navigationBarTheme,
     NavigationRailThemeData? navigationRailTheme,
     Typography? typography,
     NoDefaultCupertinoThemeData? cupertinoOverrideTheme,
@@ -1576,6 +1587,7 @@ class ThemeData with Diagnosticable {
       colorScheme: (colorScheme ?? this.colorScheme).copyWith(brightness: brightness),
       dialogTheme: dialogTheme ?? this.dialogTheme,
       floatingActionButtonTheme: floatingActionButtonTheme ?? this.floatingActionButtonTheme,
+      navigationBarTheme: navigationBarTheme ?? this.navigationBarTheme,
       navigationRailTheme: navigationRailTheme ?? this.navigationRailTheme,
       typography: typography ?? this.typography,
       cupertinoOverrideTheme: cupertinoOverrideTheme ?? this.cupertinoOverrideTheme,
@@ -1737,6 +1749,7 @@ class ThemeData with Diagnosticable {
       colorScheme: ColorScheme.lerp(a.colorScheme, b.colorScheme, t),
       dialogTheme: DialogTheme.lerp(a.dialogTheme, b.dialogTheme, t),
       floatingActionButtonTheme: FloatingActionButtonThemeData.lerp(a.floatingActionButtonTheme, b.floatingActionButtonTheme, t)!,
+      navigationBarTheme: NavigationBarThemeData.lerp(a.navigationBarTheme, b.navigationBarTheme, t)!,
       navigationRailTheme: NavigationRailThemeData.lerp(a.navigationRailTheme, b.navigationRailTheme, t)!,
       typography: Typography.lerp(a.typography, b.typography, t),
       cupertinoOverrideTheme: t < 0.5 ? a.cupertinoOverrideTheme : b.cupertinoOverrideTheme,
@@ -1826,6 +1839,7 @@ class ThemeData with Diagnosticable {
         && other.colorScheme == colorScheme
         && other.dialogTheme == dialogTheme
         && other.floatingActionButtonTheme == floatingActionButtonTheme
+        && other.navigationBarTheme == navigationBarTheme
         && other.navigationRailTheme == navigationRailTheme
         && other.typography == typography
         && other.cupertinoOverrideTheme == cupertinoOverrideTheme
@@ -1914,6 +1928,7 @@ class ThemeData with Diagnosticable {
       colorScheme,
       dialogTheme,
       floatingActionButtonTheme,
+      navigationBarTheme,
       navigationRailTheme,
       typography,
       cupertinoOverrideTheme,
@@ -1999,6 +2014,7 @@ class ThemeData with Diagnosticable {
     properties.add(DiagnosticsProperty<ColorScheme>('colorScheme', colorScheme, defaultValue: defaultData.colorScheme, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<DialogTheme>('dialogTheme', dialogTheme, defaultValue: defaultData.dialogTheme, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<FloatingActionButtonThemeData>('floatingActionButtonThemeData', floatingActionButtonTheme, defaultValue: defaultData.floatingActionButtonTheme, level: DiagnosticLevel.debug));
+    properties.add(DiagnosticsProperty<NavigationBarThemeData>('navigationBarTheme', navigationBarTheme, defaultValue: defaultData.navigationBarTheme, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<NavigationRailThemeData>('navigationRailThemeData', navigationRailTheme, defaultValue: defaultData.navigationRailTheme, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<Typography>('typography', typography, defaultValue: defaultData.typography, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<NoDefaultCupertinoThemeData>('cupertinoOverrideTheme', cupertinoOverrideTheme, defaultValue: defaultData.cupertinoOverrideTheme, level: DiagnosticLevel.debug));

packages/flutter/test/material/navigation_bar_theme_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/rendering.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  test('copyWith, ==, hashCode basics', () {
+    expect(const NavigationBarThemeData(), const NavigationBarThemeData().copyWith());
+    expect(const NavigationBarThemeData().hashCode, const NavigationBarThemeData().copyWith().hashCode);
+  });
+
+  testWidgets('Default debugFillProperties', (WidgetTester tester) async {
+    final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
+    const NavigationBarThemeData().debugFillProperties(builder);
+
+    final List<String> description = builder.properties
+        .where((DiagnosticsNode node) => !node.isFiltered(DiagnosticLevel.info))
+        .map((DiagnosticsNode node) => node.toString())
+        .toList();
+
+    expect(description, <String>[]);
+  });
+
+  testWidgets('Custom debugFillProperties', (WidgetTester tester) async {
+    final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
+    NavigationBarThemeData(
+      height: 200.0,
+      backgroundColor: const Color(0x00000099),
+      indicatorColor: const Color(0x00000098),
+      labelTextStyle: MaterialStateProperty.all(const TextStyle(fontSize: 7.0)),
+      iconTheme: MaterialStateProperty.all(const IconThemeData(color: Color(0x00000097))),
+      labelBehavior: NavigationDestinationLabelBehavior.alwaysHide,
+    ).debugFillProperties(builder);
+
+    final List<String> description = builder.properties
+        .where((DiagnosticsNode node) => !node.isFiltered(DiagnosticLevel.info))
+        .map((DiagnosticsNode node) => node.toString())
+        .toList();
+
+    expect(description[0], 'height: 200.0');
+    expect(description[1], 'backgroundColor: Color(0x00000099)');
+    expect(description[2], 'indicatorColor: Color(0x00000098)');
+    expect(description[3], 'labelTextStyle: MaterialStateProperty.all(TextStyle(inherit: true, size: 7.0))');
+
+    // Ignore instance address for IconThemeData.
+    expect(description[4].contains('iconTheme: MaterialStateProperty.all(IconThemeData'), isTrue);
+    expect(description[4].contains('(color: Color(0x00000097))'), isTrue);
+
+    expect(description[5], 'labelBehavior: NavigationDestinationLabelBehavior.alwaysHide');
+  });
+
+  testWidgets('NavigationBarThemeData values are used when no NavigationBar properties are specified', (WidgetTester tester) async {
+    const double height = 200.0;
+    const Color backgroundColor = Color(0x00000001);
+    const Color indicatorColor = Color(0x00000002);
+    const double selectedIconSize = 25.0;
+    const double unselectedIconSize = 23.0;
+    const Color selectedIconColor = Color(0x00000003);
+    const Color unselectedIconColor = Color(0x00000004);
+    const double selectedIconOpacity = 0.99;
+    const double unselectedIconOpacity = 0.98;
+    const double selectedLabelFontSize = 13.0;
+    const double unselectedLabelFontSize = 11.0;
+    const NavigationDestinationLabelBehavior labelBehavior = NavigationDestinationLabelBehavior.alwaysShow;
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Scaffold(
+          bottomNavigationBar: NavigationBarTheme(
+            data: NavigationBarThemeData(
+              height: height,
+              backgroundColor: backgroundColor,
+              indicatorColor: indicatorColor,
+              iconTheme: MaterialStateProperty.resolveWith((Set<MaterialState> states) {
+                if (states.contains(MaterialState.selected)) {
+                  return const IconThemeData(
+                    size: selectedIconSize,
+                    color: selectedIconColor,
+                    opacity: selectedIconOpacity,
+                  );
+                }
+                return const IconThemeData(
+                  size: unselectedIconSize,
+                  color: unselectedIconColor,
+                  opacity: unselectedIconOpacity,
+                );
+              }),
+              labelTextStyle: MaterialStateProperty.resolveWith((Set<MaterialState> states) {
+                if (states.contains(MaterialState.selected)) {
+                  return const TextStyle(fontSize: selectedLabelFontSize);
+                }
+                return const TextStyle(fontSize: unselectedLabelFontSize);
+              }),
+              labelBehavior: labelBehavior,
+            ),
+            child: NavigationBar(
+              selectedIndex: 0,
+              destinations: _destinations(),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    expect(_barHeight(tester), height);
+    expect(_barMaterial(tester).color, backgroundColor);
+    expect(_indicator(tester)?.color, indicatorColor);
+    expect(_selectedIconTheme(tester).size, selectedIconSize);
+    expect(_selectedIconTheme(tester).color, selectedIconColor);
+    expect(_selectedIconTheme(tester).opacity, selectedIconOpacity);
+    expect(_unselectedIconTheme(tester).size, unselectedIconSize);
+    expect(_unselectedIconTheme(tester).color, unselectedIconColor);
+    expect(_unselectedIconTheme(tester).opacity, unselectedIconOpacity);
+    expect(_selectedLabelStyle(tester).fontSize, selectedLabelFontSize);
+    expect(_unselectedLabelStyle(tester).fontSize, unselectedLabelFontSize);
+    expect(_labelBehavior(tester), labelBehavior);
+  });
+
+  testWidgets('NavigationBar values take priority over NavigationBarThemeData values when both properties are specified', (WidgetTester tester) async {
+    const double height = 200.0;
+    const Color backgroundColor = Color(0x00000001);
+    const NavigationDestinationLabelBehavior labelBehavior = NavigationDestinationLabelBehavior.alwaysShow;
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Scaffold(
+          bottomNavigationBar: NavigationBarTheme(
+            data: const NavigationBarThemeData(
+              height: 100.0,
+              backgroundColor: Color(0x00000099),
+              labelBehavior: NavigationDestinationLabelBehavior.alwaysHide,
+            ),
+            child: NavigationBar(
+              height: height,
+              backgroundColor: backgroundColor,
+              labelBehavior: labelBehavior,
+              selectedIndex: 0,
+              destinations: _destinations(),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    expect(_barHeight(tester), height);
+    expect(_barMaterial(tester).color, backgroundColor);
+    expect(_labelBehavior(tester), labelBehavior);
+  });
+}
+
+List<NavigationDestination> _destinations() {
+  return const <NavigationDestination>[
+    NavigationDestination(
+      icon: Icon(Icons.favorite_border),
+      selectedIcon: Icon(Icons.favorite),
+      label: 'Abc',
+    ),
+    NavigationDestination(
+      icon: Icon(Icons.star_border),
+      selectedIcon: Icon(Icons.star),
+      label: 'Def',
+    ),
+  ];
+}
+
+double _barHeight(WidgetTester tester) {
+  return tester.getRect(
+    find.byType(NavigationBar),
+  ).height;
+}
+
+Material _barMaterial(WidgetTester tester) {
+  return tester.firstWidget<Material>(
+    find.descendant(
+      of: find.byType(NavigationBar),
+      matching: find.byType(Material),
+    ),
+  );
+}
+
+BoxDecoration? _indicator(WidgetTester tester) {
+  return tester.firstWidget<Container>(
+    find.descendant(
+      of: find.byType(FadeTransition),
+      matching: find.byType(Container),
+    ),
+  ).decoration as BoxDecoration?;
+}
+
+IconThemeData _selectedIconTheme(WidgetTester tester) {
+  return _iconTheme(tester, Icons.favorite);
+}
+
+IconThemeData _unselectedIconTheme(WidgetTester tester) {
+  return _iconTheme(tester, Icons.star_border);
+}
+
+IconThemeData _iconTheme(WidgetTester tester, IconData icon) {
+  return tester.firstWidget<IconTheme>(
+    find.ancestor(
+      of: find.byIcon(icon),
+      matching: find.byType(IconTheme),
+    ),
+  ).data;
+}
+
+TextStyle _selectedLabelStyle(WidgetTester tester) {
+  return tester.widget<RichText>(
+    find.descendant(
+      of: find.text('Abc'),
+      matching: find.byType(RichText),
+    ),
+  ).text.style!;
+}
+
+TextStyle _unselectedLabelStyle(WidgetTester tester) {
+  return tester.widget<RichText>(
+    find.descendant(
+      of: find.text('Def'),
+      matching: find.byType(RichText),
+    ),
+  ).text.style!;
+}
+
+NavigationDestinationLabelBehavior _labelBehavior(WidgetTester tester) {
+  if (_opacityAboveLabel('Abc').evaluate().isNotEmpty && _opacityAboveLabel('Def').evaluate().isNotEmpty) {
+    return _labelOpacity(tester, 'Abc') == 1
+        ? NavigationDestinationLabelBehavior.onlyShowSelected
+        : NavigationDestinationLabelBehavior.alwaysHide;
+  } else {
+    return NavigationDestinationLabelBehavior.alwaysShow;
+  }
+}
+
+Finder _opacityAboveLabel(String text) {
+  return find.ancestor(
+    of: find.text(text),
+    matching: find.byType(Opacity),
+  );
+}
+
+// Only valid when labelBehavior != alwaysShow.
+double _labelOpacity(WidgetTester tester, String text) {
+  final Opacity opacityWidget = tester.widget<Opacity>(
+    find.ancestor(
+      of: find.text(text),
+      matching: find.byType(Opacity),
+    ),
+  );
+  return opacityWidget.opacity;
+}

packages/flutter/test/material/theme_data_test.dart

@@ -324,6 +324,7 @@ void main() {
       colorScheme: const ColorScheme.light(),
       dialogTheme: const DialogTheme(backgroundColor: Colors.black),
       floatingActionButtonTheme: const FloatingActionButtonThemeData(backgroundColor: Colors.black),
+      navigationBarTheme: const NavigationBarThemeData(backgroundColor: Colors.black),
       navigationRailTheme: const NavigationRailThemeData(backgroundColor: Colors.black),
       typography: Typography.material2018(platform: TargetPlatform.android),
       cupertinoOverrideTheme: null,
@@ -420,6 +421,7 @@ void main() {
       colorScheme: const ColorScheme.light(),
       dialogTheme: const DialogTheme(backgroundColor: Colors.white),
       floatingActionButtonTheme: const FloatingActionButtonThemeData(backgroundColor: Colors.white),
+      navigationBarTheme: const NavigationBarThemeData(backgroundColor: Colors.white),
       navigationRailTheme: const NavigationRailThemeData(backgroundColor: Colors.white),
       typography: Typography.material2018(platform: TargetPlatform.iOS),
       cupertinoOverrideTheme: ThemeData.light().cupertinoOverrideTheme,
@@ -497,6 +499,7 @@ void main() {
       colorScheme: otherTheme.colorScheme,
       dialogTheme: otherTheme.dialogTheme,
       floatingActionButtonTheme: otherTheme.floatingActionButtonTheme,
+      navigationBarTheme: otherTheme.navigationBarTheme,
       navigationRailTheme: otherTheme.navigationRailTheme,
       typography: otherTheme.typography,
       cupertinoOverrideTheme: otherTheme.cupertinoOverrideTheme,
@@ -571,6 +574,7 @@ void main() {
     expect(themeDataCopy.colorScheme, equals(otherTheme.colorScheme));
     expect(themeDataCopy.dialogTheme, equals(otherTheme.dialogTheme));
     expect(themeDataCopy.floatingActionButtonTheme, equals(otherTheme.floatingActionButtonTheme));
+    expect(themeDataCopy.navigationBarTheme, equals(otherTheme.navigationBarTheme));
     expect(themeDataCopy.navigationRailTheme, equals(otherTheme.navigationRailTheme));
     expect(themeDataCopy.typography, equals(otherTheme.typography));
     expect(themeDataCopy.cupertinoOverrideTheme, equals(otherTheme.cupertinoOverrideTheme));