[Material] Create material Banner component (#36880)

This PR creates a new material widget for the Banner component. This includes a theme as well. This widget can be dropped into any application, ideally at the top of a listview or scrollview.

packages/flutter/lib/material.dart

@@ -23,6 +23,8 @@ export 'src/material/app_bar.dart';
 export 'src/material/app_bar_theme.dart';
 export 'src/material/arc.dart';
 export 'src/material/back_button.dart';
+export 'src/material/banner.dart';
+export 'src/material/banner_theme.dart';
 export 'src/material/bottom_app_bar.dart';
 export 'src/material/bottom_app_bar_theme.dart';
 export 'src/material/bottom_navigation_bar.dart';

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

@@ -0,0 +1,166 @@
+// Copyright 2019 The Chromium 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/widgets.dart';
+
+import 'banner_theme.dart';
+import 'button_bar.dart';
+import 'button_theme.dart';
+import 'divider.dart';
+import 'theme.dart';
+
+/// A Material Design banner.
+///
+/// A banner displays an important, succinct message, and provides actions for
+/// users to address (or dismiss the banner). A user action is required for it
+/// to be dismissed.
+///
+/// Banners should be displayed at the top of the screen, below a top app bar.
+/// They are persistent and nonmodal, allowing the user to either ignore them or
+/// interact with them at any time.
+///
+/// The [actions] will be placed beside the [content] if there is only one.
+/// Otherwise, the [actions] will be placed below the [content]. Use
+/// [forceActionsBelow] to override this behavior.
+///
+/// The [actions] and [content] must be provided. An optional leading widget
+/// (typically an [Image]) can also be provided. The [contentTextStyle] and
+/// [backgroundColor] can be provided to customize the banner.
+///
+/// This widget is unrelated to the widgets library [Banner] widget.
+class MaterialBanner extends StatelessWidget {
+  /// Creates a [MaterialBanner].
+  ///
+  /// The [actions], [content], and [forceActionsBelow] must be non-null.
+  /// The [actions.length] must be greater than 0.
+  const MaterialBanner({
+    Key key,
+    @required this.content,
+    this.contentTextStyle,
+    @required this.actions,
+    this.leading,
+    this.backgroundColor,
+    this.padding,
+    this.leadingPadding,
+    this.forceActionsBelow = false,
+  }) : assert(content != null),
+       assert(actions != null),
+       assert(forceActionsBelow != null),
+       super(key: key);
+
+  /// The content of the [MaterialBanner].
+  ///
+  /// Typically a [Text] widget.
+  final Widget content;
+
+  /// Style for the text in the [content] of the [MaterialBanner].
+  ///
+  /// If `null`, [MaterialBannerThemeData.contentTextStyle] is used. If that is
+  /// also `null`, [ThemeData.textTheme.body1] is used.
+  final TextStyle contentTextStyle;
+
+  /// The set of actions that are displayed at the bottom or trailing side of
+  /// the [MaterialBanner].
+  ///
+  /// Typically this is a list of [FlatButton] widgets.
+  ///
+  /// These widgets will be wrapped in a [ButtonBar], which introduces 8 pixels
+  /// of padding on each side.
+  final List<Widget> actions;
+
+  /// The (optional) leading widget of the [MaterialBanner].
+  ///
+  /// Typically an [Icon] widget.
+  final Widget leading;
+
+  /// The color of the surface of this [MaterialBanner].
+  ///
+  /// If `null`, [MaterialBannerThemeData.backgroundColor] is used. If that is
+  /// also `null`, [ThemeData.colorScheme.surface] is used.
+  final Color backgroundColor;
+
+  /// The amount of space by which to inset the [content].
+  ///
+  /// If the [actions] are below the [content], this defaults to
+  /// `EdgeInsetsDirectional.only(start: 16.0, top: 24.0, end: 16.0, bottom: 4.0)`.
+  ///
+  /// If the [actions] are trailing the [content], this defaults to
+  /// `EdgeInsetsDirectional.only(start: 16.0, top: 2.0)`.
+  final EdgeInsetsGeometry padding;
+
+  /// The amount of space by which to inset the [leading] widget.
+  ///
+  /// This defaults to `EdgeInsetsDirectional.only(end: 16.0)`.
+  final EdgeInsetsGeometry leadingPadding;
+
+  /// An override to force the [actions] to be below the [content] regardless of
+  /// how many there are.
+  ///
+  /// If this is `true`, the [actions] will be placed below the [content]. If
+  /// this is `false`, the [actions] will be placed on the trailing side of the
+  /// [content] if [actions.length] is `1` and below the [content] if greater
+  /// than `1`.
+  final bool forceActionsBelow;
+
+  @override
+  Widget build(BuildContext context) {
+    assert(actions.isNotEmpty);
+
+    final ThemeData theme = Theme.of(context);
+    final MaterialBannerThemeData bannerTheme = MaterialBannerTheme.of(context);
+
+    final bool isSingleRow = actions.length == 1 && !forceActionsBelow;
+    final EdgeInsetsGeometry padding = this.padding ?? bannerTheme.padding ?? (isSingleRow
+        ? const EdgeInsetsDirectional.only(start: 16.0, top: 2.0)
+        : const EdgeInsetsDirectional.only(start: 16.0, top: 24.0, end: 16.0, bottom: 4.0));
+    final EdgeInsetsGeometry leadingPadding = this.leadingPadding
+        ?? bannerTheme.padding
+        ?? const EdgeInsetsDirectional.only(end: 16.0);
+
+    final Widget buttonBar = ButtonTheme.bar(
+      layoutBehavior: ButtonBarLayoutBehavior.constrained,
+      child: ButtonBar(
+        children: actions,
+      ),
+    );
+
+    final Color backgroundColor = this.backgroundColor
+        ?? bannerTheme.backgroundColor
+        ?? theme.colorScheme.surface;
+    final TextStyle textStyle = contentTextStyle
+        ?? bannerTheme.contentTextStyle
+        ?? theme.textTheme.body1;
+
+    return Container(
+      color: backgroundColor,
+      child: Column(
+        children: <Widget>[
+          Padding(
+            padding: padding,
+            child: Row(
+              children: <Widget>[
+                if (leading != null)
+                  Padding(
+                    padding: leadingPadding,
+                    child: leading,
+                  ),
+                Flexible(
+                  child: DefaultTextStyle(
+                    style: textStyle,
+                    child: content,
+                  ),
+                ),
+                if (isSingleRow)
+                  buttonBar,
+              ],
+            ),
+          ),
+          if (!isSingleRow)
+            buttonBar,
+          const Divider(height: 0),
+        ],
+      ),
+    );
+  }
+}

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

@@ -0,0 +1,149 @@
+// Copyright 2019 The Chromium 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/foundation.dart';
+import 'package:flutter/widgets.dart';
+
+import 'theme.dart';
+
+/// Defines the visual properties of [MaterialBanner] widgets.
+///
+/// Descendant widgets obtain the current [MaterialBannerThemeData] object using
+/// `MaterialBannerTheme.of(context)`. Instances of [MaterialBannerThemeData]
+/// can be customized with [MaterialBannerThemeData.copyWith].
+///
+/// Typically a [MaterialBannerThemeData] is specified as part of the overall
+/// [Theme] with [ThemeData.bannerTheme].
+///
+/// All [MaterialBannerThemeData] properties are `null` by default. When null,
+/// the [MaterialBanner] will provide its own defaults.
+///
+/// See also:
+///
+///  * [ThemeData], which describes the overall theme information for the
+///    application.
+class MaterialBannerThemeData extends Diagnosticable {
+
+  /// Creates a theme that can be used for [MaterialBannerTheme] or
+  /// [ThemeData.bannerTheme].
+  const MaterialBannerThemeData({
+    this.backgroundColor,
+    this.contentTextStyle,
+    this.padding,
+    this.leadingPadding,
+  });
+
+  /// The background color of a [MaterialBanner].
+  final Color backgroundColor;
+
+  /// Used to configure the [DefaultTextStyle] for the [MaterialBanner.content]
+  /// widget.
+  final TextStyle contentTextStyle;
+
+  /// The amount of space by which to inset [MaterialBanner.content].
+  final EdgeInsetsGeometry padding;
+
+  /// The amount of space by which to inset [MaterialBanner.leading].
+  final EdgeInsetsGeometry leadingPadding;
+
+  /// Creates a copy of this object with the given fields replaced with the
+  /// new values.
+  MaterialBannerThemeData copyWith({
+    Color backgroundColor,
+    TextStyle contentTextStyle,
+    EdgeInsetsGeometry padding,
+    EdgeInsetsGeometry leadingPadding,
+  }) {
+    return MaterialBannerThemeData(
+      backgroundColor: backgroundColor ?? this.backgroundColor,
+      contentTextStyle: contentTextStyle ?? this.contentTextStyle,
+      padding: padding ?? this.padding,
+      leadingPadding: leadingPadding ?? this.leadingPadding,
+    );
+  }
+
+  /// Linearly interpolate between two Banner themes.
+  ///
+  /// The argument `t` must not be null.
+  ///
+  /// {@macro dart.ui.shadow.lerp}
+  static MaterialBannerThemeData lerp(MaterialBannerThemeData a, MaterialBannerThemeData b, double t) {
+    assert(t != null);
+    return MaterialBannerThemeData(
+      backgroundColor: Color.lerp(a?.backgroundColor, b?.backgroundColor, t),
+      contentTextStyle: TextStyle.lerp(a?.contentTextStyle, b?.contentTextStyle, t),
+      padding: EdgeInsets.lerp(a?.padding, b?.padding, t),
+      leadingPadding: EdgeInsets.lerp(a?.leadingPadding, b?.leadingPadding, t),
+    );
+  }
+
+  @override
+  int get hashCode {
+    return hashValues(
+      backgroundColor,
+      contentTextStyle,
+      padding,
+      leadingPadding,
+    );
+  }
+
+  @override
+  bool operator ==(dynamic other) {
+    if (identical(this, other))
+      return true;
+    if (other.runtimeType != runtimeType)
+      return false;
+    final MaterialBannerThemeData typedOther = other;
+    return typedOther.backgroundColor == backgroundColor
+        && typedOther.contentTextStyle == contentTextStyle
+        && typedOther.padding == padding
+        && typedOther.leadingPadding == leadingPadding;
+  }
+
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+    super.debugFillProperties(properties);
+    properties.add(ColorProperty('backgroundColor', backgroundColor, defaultValue: null));
+    properties.add(DiagnosticsProperty<TextStyle>('contentTextStyle', contentTextStyle, defaultValue: null));
+    properties.add(DiagnosticsProperty<EdgeInsetsGeometry>('padding', padding, defaultValue: null));
+    properties.add(DiagnosticsProperty<EdgeInsetsGeometry>('leadingPadding', leadingPadding, defaultValue: null));
+  }
+}
+
+/// An inherited widget that defines the configuration for
+/// [MaterialBanner]s in this widget's subtree.
+///
+/// Values specified here are used for [MaterialBanner] properties that are not
+/// given an explicit non-null value.
+class MaterialBannerTheme extends InheritedWidget {
+  /// Creates a banner theme that controls the configurations for
+  /// [MaterialBanner]s in its widget subtree.
+  const MaterialBannerTheme({
+    Key key,
+    this.data,
+    Widget child,
+  }) : super(key: key, child: child);
+
+  /// The properties for descendant [MaterialBanner] widgets.
+  final MaterialBannerThemeData data;
+
+  /// The closest instance of this class's [data] value that encloses the given
+  /// context.
+  ///
+  /// If there is no ancestor, it returns [ThemeData.bannerTheme]. Applications
+  /// can assume that the returned value will not be null.
+  ///
+  /// Typical usage is as follows:
+  ///
+  /// ```dart
+  /// MaterialBannerThemeData theme = MaterialBannerTheme.of(context);
+  /// ```
+  static MaterialBannerThemeData of(BuildContext context) {
+    final MaterialBannerTheme popupMenuTheme = context.inheritFromWidgetOfExactType(MaterialBannerTheme);
+    return popupMenuTheme?.data ?? Theme.of(context).bannerTheme;
+  }
+
+  @override
+  bool updateShouldNotify(MaterialBannerTheme oldWidget) => data != oldWidget.data;
+}

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

@@ -10,6 +10,7 @@ import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 
 import 'app_bar_theme.dart';
+import 'banner_theme.dart';
 import 'bottom_app_bar_theme.dart';
 import 'bottom_sheet_theme.dart';
 import 'button_theme.dart';
@@ -176,6 +177,7 @@ class ThemeData extends Diagnosticable {
     SnackBarThemeData snackBarTheme,
     BottomSheetThemeData bottomSheetTheme,
     PopupMenuThemeData popupMenuTheme,
+    MaterialBannerThemeData bannerTheme,
   }) {
     brightness ??= Brightness.light;
     final bool isDark = brightness == Brightness.dark;
@@ -279,6 +281,7 @@ class ThemeData extends Diagnosticable {
     snackBarTheme ??= const SnackBarThemeData();
     bottomSheetTheme ??= const BottomSheetThemeData();
     popupMenuTheme ??= const PopupMenuThemeData();
+    bannerTheme ??= const MaterialBannerThemeData();
 
     return ThemeData.raw(
       brightness: brightness,
@@ -340,6 +343,7 @@ class ThemeData extends Diagnosticable {
       snackBarTheme: snackBarTheme,
       bottomSheetTheme: bottomSheetTheme,
       popupMenuTheme: popupMenuTheme,
+      bannerTheme: bannerTheme,
     );
   }
 
@@ -413,6 +417,7 @@ class ThemeData extends Diagnosticable {
     @required this.snackBarTheme,
     @required this.bottomSheetTheme,
     @required this.popupMenuTheme,
+    @required this.bannerTheme,
   }) : assert(brightness != null),
        assert(primaryColor != null),
        assert(primaryColorBrightness != null),
@@ -468,7 +473,8 @@ class ThemeData extends Diagnosticable {
        assert(typography != null),
        assert(snackBarTheme != null),
        assert(bottomSheetTheme != null),
-       assert(popupMenuTheme != null);
+       assert(popupMenuTheme != null),
+       assert(bannerTheme != null);
 
   // Warning: make sure these properties are in the exact same order as in
   // hashValues() and in the raw constructor and in the order of fields in
@@ -798,6 +804,9 @@ class ThemeData extends Diagnosticable {
   /// popup menus.
   final PopupMenuThemeData popupMenuTheme;
 
+  /// A theme for customizing the color and text style of a [MaterialBanner].
+  final MaterialBannerThemeData bannerTheme;
+
   /// Creates a copy of this theme but with the given fields replaced with the new values.
   ThemeData copyWith({
     Brightness brightness,
@@ -859,6 +868,7 @@ class ThemeData extends Diagnosticable {
     SnackBarThemeData snackBarTheme,
     BottomSheetThemeData bottomSheetTheme,
     PopupMenuThemeData popupMenuTheme,
+    MaterialBannerThemeData bannerTheme,
   }) {
     cupertinoOverrideTheme = cupertinoOverrideTheme?.noDefault();
     return ThemeData.raw(
@@ -921,6 +931,7 @@ class ThemeData extends Diagnosticable {
       snackBarTheme: snackBarTheme ?? this.snackBarTheme,
       bottomSheetTheme: bottomSheetTheme ?? this.bottomSheetTheme,
       popupMenuTheme: popupMenuTheme ?? this.popupMenuTheme,
+      bannerTheme: bannerTheme ?? this.bannerTheme,
     );
   }
 
@@ -1061,6 +1072,7 @@ class ThemeData extends Diagnosticable {
       snackBarTheme: SnackBarThemeData.lerp(a.snackBarTheme, b.snackBarTheme, t),
       bottomSheetTheme: BottomSheetThemeData.lerp(a.bottomSheetTheme, b.bottomSheetTheme, t),
       popupMenuTheme: PopupMenuThemeData.lerp(a.popupMenuTheme, b.popupMenuTheme, t),
+      bannerTheme: MaterialBannerThemeData.lerp(a.bannerTheme, b.bannerTheme, t),
     );
   }
 
@@ -1128,7 +1140,8 @@ class ThemeData extends Diagnosticable {
            (otherData.cupertinoOverrideTheme == cupertinoOverrideTheme) &&
            (otherData.snackBarTheme == snackBarTheme) &&
            (otherData.bottomSheetTheme == bottomSheetTheme) &&
-           (otherData.popupMenuTheme == popupMenuTheme);
+           (otherData.popupMenuTheme == popupMenuTheme) &&
+           (otherData.bannerTheme == bannerTheme);
   }
 
   @override
@@ -1196,6 +1209,7 @@ class ThemeData extends Diagnosticable {
       snackBarTheme,
       bottomSheetTheme,
       popupMenuTheme,
+      bannerTheme,
     ];
     return hashList(values);
   }
@@ -1260,6 +1274,7 @@ class ThemeData extends Diagnosticable {
     properties.add(DiagnosticsProperty<SnackBarThemeData>('snackBarTheme', snackBarTheme, defaultValue: defaultData.snackBarTheme));
     properties.add(DiagnosticsProperty<BottomSheetThemeData>('bottomSheetTheme', bottomSheetTheme, defaultValue: defaultData.bottomSheetTheme));
     properties.add(DiagnosticsProperty<PopupMenuThemeData>('popupMenuTheme', popupMenuTheme, defaultValue: defaultData.popupMenuTheme));
+    properties.add(DiagnosticsProperty<MaterialBannerThemeData>('bannerTheme', bannerTheme, defaultValue: defaultData.bannerTheme));
   }
 }
 

packages/flutter/test/material/banner_test.dart

@@ -0,0 +1,134 @@
+// Copyright 2019 The Chromium 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() {
+  testWidgets('Custom background color respected', (WidgetTester tester) async {
+    const Color color = Colors.pink;
+    await tester.pumpWidget(
+      MaterialApp(
+        home: MaterialBanner(
+          backgroundColor: color,
+          content: const Text('I am a banner'),
+          actions: <Widget>[
+            FlatButton(
+              child: const Text('Action'),
+              onPressed: () { },
+            ),
+          ],
+        ),
+      ),
+    );
+
+    final Container container = _getContainerFromBanner(tester);
+    expect(container.decoration, const BoxDecoration(color: color));
+  });
+
+  testWidgets('Custom content TextStyle respected', (WidgetTester tester) async {
+    const String contentText = 'Content';
+    const TextStyle contentTextStyle = TextStyle(color: Colors.pink);
+    await tester.pumpWidget(
+      MaterialApp(
+        home: MaterialBanner(
+          contentTextStyle: contentTextStyle,
+          content: const Text(contentText),
+          actions: <Widget>[
+            FlatButton(
+              child: const Text('Action'),
+              onPressed: () { },
+            ),
+          ],
+        ),
+      ),
+    );
+
+    final RenderParagraph content = _getTextRenderObjectFromDialog(tester, contentText);
+    expect(content.text.style, contentTextStyle);
+  });
+
+  testWidgets('Actions laid out below content if more than one action', (WidgetTester tester) async {
+    const String contentText = 'Content';
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: MaterialBanner(
+          content: const Text(contentText),
+          actions: <Widget>[
+            FlatButton(
+              child: const Text('Action 1'),
+              onPressed: () { },
+            ),
+            FlatButton(
+              child: const Text('Action 2'),
+              onPressed: () { },
+            ),
+          ],
+        ),
+      ),
+    );
+
+    final Offset contentBottomLeft = tester.getBottomLeft(find.text(contentText));
+    final Offset actionsTopRight = tester.getTopLeft(find.byType(ButtonBar));
+    expect(contentBottomLeft.dy, lessThan(actionsTopRight.dy));
+    expect(contentBottomLeft.dx, greaterThan(actionsTopRight.dx));
+  });
+
+  testWidgets('Actions laid out beside content if only one action', (WidgetTester tester) async {
+    const String contentText = 'Content';
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: MaterialBanner(
+          content: const Text(contentText),
+          actions: <Widget>[
+            FlatButton(
+              child: const Text('Action'),
+              onPressed: () { },
+            ),
+          ],
+        ),
+      ),
+    );
+
+    final Offset contentBottomLeft = tester.getBottomLeft(find.text(contentText));
+    final Offset actionsTopRight = tester.getTopRight(find.byType(ButtonBar));
+    expect(contentBottomLeft.dy, greaterThan(actionsTopRight.dy));
+    expect(contentBottomLeft.dx, lessThan(actionsTopRight.dx));
+  });
+
+  testWidgets('Actions laid out below content if forced override', (WidgetTester tester) async {
+    const String contentText = 'Content';
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: MaterialBanner(
+          forceActionsBelow: true,
+          content: const Text(contentText),
+          actions: <Widget>[
+            FlatButton(
+              child: const Text('Action'),
+              onPressed: () { },
+            ),
+          ],
+        ),
+      ),
+    );
+
+    final Offset contentBottomLeft = tester.getBottomLeft(find.text(contentText));
+    final Offset actionsTopRight = tester.getTopLeft(find.byType(ButtonBar));
+    expect(contentBottomLeft.dy, lessThan(actionsTopRight.dy));
+    expect(contentBottomLeft.dx, greaterThan(actionsTopRight.dx));
+  });
+}
+
+Container _getContainerFromBanner(WidgetTester tester) {
+  return tester.widget<Container>(find.descendant(of: find.byType(MaterialBanner), matching: find.byType(Container)).first);
+}
+
+RenderParagraph _getTextRenderObjectFromDialog(WidgetTester tester, String text) {
+  return tester.element<StatelessElement>(find.descendant(of: find.byType(MaterialBanner), matching: find.text(text))).renderObject;
+}

packages/flutter/test/material/banner_theme_test.dart

@@ -0,0 +1,190 @@
+// Copyright 2019 The Chromium 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('MaterialBannerThemeData copyWith, ==, hashCode basics', () {
+    expect(const MaterialBannerThemeData(), const MaterialBannerThemeData().copyWith());
+    expect(const MaterialBannerThemeData().hashCode, const MaterialBannerThemeData().copyWith().hashCode);
+  });
+
+  test('MaterialBannerThemeData null fields by default', () {
+    const MaterialBannerThemeData bannerTheme = MaterialBannerThemeData();
+    expect(bannerTheme.backgroundColor, null);
+    expect(bannerTheme.contentTextStyle, null);
+  });
+
+  testWidgets('Default MaterialBannerThemeData debugFillProperties', (WidgetTester tester) async {
+    final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
+    const MaterialBannerThemeData().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('MaterialBannerThemeData implements debugFillProperties', (WidgetTester tester) async {
+    final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
+    const MaterialBannerThemeData(
+      backgroundColor: Color(0xFFFFFFFF),
+      contentTextStyle: TextStyle(color: Color(0xFFFFFFFF)),
+    ).debugFillProperties(builder);
+
+    final List<String> description = builder.properties
+        .where((DiagnosticsNode node) => !node.isFiltered(DiagnosticLevel.info))
+        .map((DiagnosticsNode node) => node.toString())
+        .toList();
+
+    expect(description, <String>[
+      'backgroundColor: Color(0xffffffff)',
+      'contentTextStyle: TextStyle(inherit: true, color: Color(0xffffffff))',
+    ]);
+  });
+
+  testWidgets('Passing no MaterialBannerThemeData returns defaults', (WidgetTester tester) async {
+    const String contentText = 'Content';
+    await tester.pumpWidget(MaterialApp(
+      home: Scaffold(
+        body: MaterialBanner(
+          content: const Text(contentText),
+          actions: <Widget>[
+            FlatButton(
+              child: const Text('Action'),
+              onPressed: () { },
+            ),
+          ],
+        ),
+      ),
+    ));
+
+    final Container container = _getContainerFromBanner(tester);
+    final RenderParagraph content = _getTextRenderObjectFromDialog(tester, contentText);
+    expect(container.decoration, const BoxDecoration(color: Color(0xffffffff)));
+    expect(content.text.style, Typography().englishLike.body1.merge(Typography().black.body1));
+  });
+
+  testWidgets('MaterialBanner uses values from MaterialBannerThemeData', (WidgetTester tester) async {
+    final MaterialBannerThemeData bannerTheme = _bannerTheme();
+    const String contentText = 'Content';
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData(bannerTheme: bannerTheme),
+      home: Scaffold(
+        body: MaterialBanner(
+          leading: const Icon(Icons.ac_unit),
+          content: const Text(contentText),
+          actions: <Widget>[
+            FlatButton(
+              child: const Text('Action'),
+              onPressed: () { },
+            ),
+          ],
+        ),
+      ),
+    ));
+
+    final Container container = _getContainerFromBanner(tester);
+    final RenderParagraph content = _getTextRenderObjectFromDialog(tester, contentText);
+    expect(container.decoration, BoxDecoration(color: bannerTheme.backgroundColor));
+    expect(content.text.style, bannerTheme.contentTextStyle);
+
+    final Offset contentTopLeft = tester.getTopLeft(_textFinder(contentText));
+    final Offset containerTopLeft = tester.getTopLeft(_containerFinder());
+    final Offset leadingTopLeft = tester.getTopLeft(find.byIcon(Icons.ac_unit));
+    expect(contentTopLeft.dy - containerTopLeft.dy, 24);
+    expect(contentTopLeft.dx - containerTopLeft.dx, 39);
+    expect(leadingTopLeft.dy - containerTopLeft.dy, 19);
+    expect(leadingTopLeft.dx - containerTopLeft.dx, 10);
+  });
+
+  testWidgets('MaterialBanner widget properties take priority over theme', (WidgetTester tester) async {
+    const Color backgroundColor = Colors.purple;
+    const TextStyle textStyle = TextStyle(color: Colors.green);
+    final MaterialBannerThemeData bannerTheme = _bannerTheme();
+    const String contentText = 'Content';
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData(bannerTheme: bannerTheme),
+      home: Scaffold(
+        body: MaterialBanner(
+          backgroundColor: backgroundColor,
+          leading: const Icon(Icons.ac_unit),
+          contentTextStyle: textStyle,
+          content: const Text(contentText),
+          padding: const EdgeInsets.all(10),
+          leadingPadding: const EdgeInsets.all(10),
+          actions: <Widget>[
+            FlatButton(
+              child: const Text('Action'),
+              onPressed: () { },
+            ),
+          ],
+        ),
+      ),
+    ));
+
+    final Container container = _getContainerFromBanner(tester);
+    final RenderParagraph content = _getTextRenderObjectFromDialog(tester, contentText);
+    expect(container.decoration, const BoxDecoration(color: backgroundColor));
+    expect(content.text.style, textStyle);
+
+    final Offset contentTopLeft = tester.getTopLeft(_textFinder(contentText));
+    final Offset containerTopLeft = tester.getTopLeft(_containerFinder());
+    final Offset leadingTopLeft = tester.getTopLeft(find.byIcon(Icons.ac_unit));
+    expect(contentTopLeft.dy - containerTopLeft.dy, 29);
+    expect(contentTopLeft.dx - containerTopLeft.dx, 54);
+    expect(leadingTopLeft.dy - containerTopLeft.dy, 24);
+    expect(leadingTopLeft.dx - containerTopLeft.dx, 20);
+  });
+
+  testWidgets('MaterialBanner uses color scheme when necessary', (WidgetTester tester) async {
+    final ColorScheme colorScheme = const ColorScheme.light().copyWith(surface: Colors.purple);
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData(colorScheme: colorScheme),
+      home: Scaffold(
+        body: MaterialBanner(
+          content: const Text('Content'),
+          actions: <Widget>[
+            FlatButton(
+              child: const Text('Action'),
+              onPressed: () { },
+            ),
+          ],
+        ),
+      ),
+    ));
+
+    final Container container = _getContainerFromBanner(tester);
+    expect(container.decoration, BoxDecoration(color: colorScheme.surface));
+  });
+}
+
+MaterialBannerThemeData _bannerTheme() {
+  return const MaterialBannerThemeData(
+    backgroundColor: Colors.orange,
+    contentTextStyle: TextStyle(color: Colors.pink),
+    padding: EdgeInsets.all(5),
+    leadingPadding: EdgeInsets.all(5),
+  );
+}
+
+Container _getContainerFromBanner(WidgetTester tester) {
+  return tester.widget<Container>(_containerFinder());
+}
+
+Finder _containerFinder() {
+  return find.descendant(of: find.byType(MaterialBanner), matching: find.byType(Container)).first;
+}
+
+RenderParagraph _getTextRenderObjectFromDialog(WidgetTester tester, String text) {
+  return tester.element<StatelessElement>(_textFinder(text)).renderObject;
+}
+
+Finder _textFinder(String text) {
+  return find.descendant(of: find.byType(MaterialBanner), matching: find.text(text));
+}