Add `ExpansionTileTheme` (#98405)

packages/flutter/lib/material.dart

@@ -73,6 +73,7 @@ export 'src/material/elevation_overlay.dart';
 export 'src/material/expand_icon.dart';
 export 'src/material/expansion_panel.dart';
 export 'src/material/expansion_tile.dart';
+export 'src/material/expansion_tile_theme.dart';
 export 'src/material/feedback.dart';
 export 'src/material/flat_button.dart';
 export 'src/material/flexible_space_bar.dart';

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

@@ -6,6 +6,7 @@ import 'package:flutter/widgets.dart';
 
 import 'color_scheme.dart';
 import 'colors.dart';
+import 'expansion_tile_theme.dart';
 import 'icons.dart';
 import 'list_tile.dart';
 import 'theme.dart';
@@ -107,9 +108,25 @@ class ExpansionTile extends StatefulWidget {
   final List<Widget> children;
 
   /// The color to display behind the sublist when expanded.
+  ///
+  /// If this property is null then [ExpansionTileThemeData.backgroundColor] is used. If that
+  /// is also null then Colors.transparent is used.
+  ///
+  /// See also:
+  ///
+  /// * [ExpansionTileTheme.of], which returns the nearest [ExpansionTileTheme]'s
+  ///   [ExpansionTileThemeData].
   final Color? backgroundColor;
 
   /// When not null, defines the background color of tile when the sublist is collapsed.
+  ///
+  /// If this property is null then [ExpansionTileThemeData.collapsedBackgroundColor] is used.
+  /// If that is also null then Colors.transparent is used.
+  ///
+  /// See also:
+  ///
+  /// * [ExpansionTileTheme.of], which returns the nearest [ExpansionTileTheme]'s
+  ///   [ExpansionTileThemeData].
   final Color? collapsedBackgroundColor;
 
   /// A widget to display after the title.
@@ -134,7 +151,13 @@ class ExpansionTile extends StatefulWidget {
   /// the [leading], [title], [subtitle] and [trailing] widgets. It does not inset
   /// the expanded [children] widgets.
   ///
-  /// When the value is null, the tile's padding is `EdgeInsets.symmetric(horizontal: 16.0)`.
+  /// If this property is null then [ExpansionTileThemeData.tilePadding] is used. If that
+  /// is also null then the tile's padding is `EdgeInsets.symmetric(horizontal: 16.0)`.
+  ///
+  /// See also:
+  ///
+  /// * [ExpansionTileTheme.of], which returns the nearest [ExpansionTileTheme]'s
+  ///   [ExpansionTileThemeData].
   final EdgeInsetsGeometry? tilePadding;
 
   /// Specifies the alignment of [children], which are arranged in a column when
@@ -150,7 +173,13 @@ class ExpansionTile extends StatefulWidget {
   ///
   /// The width of the column is the width of the widest child widget in [children].
   ///
-  /// When the value is null, the value of `expandedAlignment` is [Alignment.center].
+  /// If this property is null then [ExpansionTileThemeData.expandedAlignment]is used. If that
+  /// is also null then the value of `expandedAlignment` is [Alignment.center].
+  ///
+  /// See also:
+  ///
+  /// * [ExpansionTileTheme.of], which returns the nearest [ExpansionTileTheme]'s
+  ///   [ExpansionTileThemeData].
   final Alignment? expandedAlignment;
 
   /// Specifies the alignment of each child within [children] when the tile is expanded.
@@ -171,12 +200,26 @@ class ExpansionTile extends StatefulWidget {
 
   /// Specifies padding for [children].
   ///
-  /// When the value is null, the value of `childrenPadding` is [EdgeInsets.zero].
+  /// If this property is null then [ExpansionTileThemeData.childrenPadding] is used. If that
+  /// is also null then the value of `childrenPadding` is [EdgeInsets.zero].
+  ///
+  /// See also:
+  ///
+  /// * [ExpansionTileTheme.of], which returns the nearest [ExpansionTileTheme]'s
+  ///   [ExpansionTileThemeData].
   final EdgeInsetsGeometry? childrenPadding;
 
   /// The icon color of tile's expansion arrow icon when the sublist is expanded.
   ///
   /// Used to override to the [ListTileThemeData.iconColor].
+  ///
+  /// If this property is null then [ExpansionTileThemeData.iconColor] is used. If that
+  /// is also null then the value of [ListTileThemeData.iconColor] is used.
+  ///
+  /// See also:
+  ///
+  /// * [ExpansionTileTheme.of], which returns the nearest [ExpansionTileTheme]'s
+  ///   [ExpansionTileThemeData].
   final Color? iconColor;
 
   /// The icon color of tile's expansion arrow icon when the sublist is collapsed.
@@ -188,11 +231,27 @@ class ExpansionTile extends StatefulWidget {
   /// The color of the tile's titles when the sublist is expanded.
   ///
   /// Used to override to the [ListTileThemeData.textColor].
+  ///
+  /// If this property is null then [ExpansionTileThemeData.textColor] is used. If that
+  /// is also null then the value of [ListTileThemeData.textColor] is used.
+  ///
+  /// See also:
+  ///
+  /// * [ExpansionTileTheme.of], which returns the nearest [ExpansionTileTheme]'s
+  ///   [ExpansionTileThemeData].
   final Color? textColor;
 
   /// The color of the tile's titles when the sublist is collapsed.
   ///
   /// Used to override to the [ListTileThemeData.textColor].
+  ///
+  /// If this property is null then [ExpansionTileThemeData.collapsedTextColor] is used. If that
+  /// is also null then the value of [ListTileThemeData.textColor] is used.
+  ///
+  /// See also:
+  ///
+  /// * [ExpansionTileTheme.of], which returns the nearest [ExpansionTileTheme]'s
+  ///   [ExpansionTileThemeData].
   final Color? collapsedTextColor;
 
   /// Typically used to force the expansion arrow icon to the tile's leading or trailing edge.
@@ -297,11 +356,12 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
   }
 
   Widget _buildChildren(BuildContext context, Widget? child) {
+    final ExpansionTileThemeData expansionTileTheme = ExpansionTileTheme.of(context);
     final Color borderSideColor = _borderColor.value ?? Colors.transparent;
 
     return Container(
       decoration: BoxDecoration(
-        color: _backgroundColor.value ?? Colors.transparent,
+        color: _backgroundColor.value ?? expansionTileTheme.backgroundColor ?? Colors.transparent,
         border: Border(
           top: BorderSide(color: borderSideColor),
           bottom: BorderSide(color: borderSideColor),
@@ -311,11 +371,11 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
         mainAxisSize: MainAxisSize.min,
         children: <Widget>[
           ListTileTheme.merge(
-            iconColor: _iconColor.value,
+            iconColor: _iconColor.value ?? expansionTileTheme.iconColor,
             textColor: _headerColor.value,
             child: ListTile(
               onTap: _handleTap,
-              contentPadding: widget.tilePadding,
+              contentPadding: widget.tilePadding ?? expansionTileTheme.tilePadding,
               leading: widget.leading ?? _buildLeadingIcon(context),
               title: widget.title,
               subtitle: widget.subtitle,
@@ -324,7 +384,9 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
           ),
           ClipRect(
             child: Align(
-              alignment: widget.expandedAlignment ?? Alignment.center,
+              alignment: widget.expandedAlignment
+                ?? expansionTileTheme.expandedAlignment
+                ?? Alignment.center,
               heightFactor: _heightFactor.value,
               child: child,
             ),
@@ -337,22 +399,28 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
   @override
   void didChangeDependencies() {
     final ThemeData theme = Theme.of(context);
+    final ExpansionTileThemeData expansionTileTheme = ExpansionTileTheme.of(context);
     final ColorScheme colorScheme = theme.colorScheme;
     _borderColorTween.end = theme.dividerColor;
     _headerColorTween
-      ..begin = widget.collapsedTextColor ?? theme.textTheme.subtitle1!.color
-      ..end = widget.textColor ?? colorScheme.primary;
+      ..begin = widget.collapsedTextColor
+        ?? expansionTileTheme.collapsedTextColor
+        ?? theme.textTheme.subtitle1!.color
+      ..end = widget.textColor ?? expansionTileTheme.textColor ?? colorScheme.primary;
     _iconColorTween
-      ..begin = widget.collapsedIconColor ?? theme.unselectedWidgetColor
-      ..end = widget.iconColor ?? colorScheme.primary;
+      ..begin = widget.collapsedIconColor
+        ?? expansionTileTheme.collapsedIconColor
+        ?? theme.unselectedWidgetColor
+      ..end = widget.iconColor ?? expansionTileTheme.iconColor ?? colorScheme.primary;
     _backgroundColorTween
-      ..begin = widget.collapsedBackgroundColor
-      ..end = widget.backgroundColor;
+      ..begin = widget.collapsedBackgroundColor ?? expansionTileTheme.collapsedBackgroundColor
+      ..end = widget.backgroundColor ?? expansionTileTheme.backgroundColor;
     super.didChangeDependencies();
   }
 
   @override
   Widget build(BuildContext context) {
+    final ExpansionTileThemeData expansionTileTheme = ExpansionTileTheme.of(context);
     final bool closed = !_isExpanded && _controller.isDismissed;
     final bool shouldRemoveChildren = closed && !widget.maintainState;
 
@@ -361,7 +429,7 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
       child: TickerMode(
         enabled: !closed,
         child: Padding(
-          padding: widget.childrenPadding ?? EdgeInsets.zero,
+          padding: widget.childrenPadding ?? expansionTileTheme.childrenPadding ?? EdgeInsets.zero,
           child: Column(
             crossAxisAlignment: widget.expandedCrossAxisAlignment ?? CrossAxisAlignment.center,
             children: widget.children,

packages/flutter/lib/src/material/expansion_tile_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';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/widgets.dart';
+
+import 'theme.dart';
+
+/// Used with [ExpansionTileTheme] to define default property values for
+/// descendant [ExpansionTile] widgets.
+///
+/// Descendant widgets obtain the current [ExpansionTileThemeData] object
+/// using `ExpansionTileTheme.of(context)`. Instances of
+/// [ExpansionTileThemeData] can be customized with
+/// [ExpansionTileThemeData.copyWith].
+///
+/// A [ExpansionTileThemeData] is often specified as part of the
+/// overall [Theme] with [ThemeData.expansionTileTheme].
+///
+/// All [ExpansionTileThemeData] properties are `null` by default.
+/// When a theme property is null, the [ExpansionTile]  will provide its own
+/// default based on the overall [Theme]'s textTheme and
+/// colorScheme. See the individual [ExpansionTile] properties for details.
+///
+/// See also:
+///
+///  * [ThemeData], which describes the overall theme information for the
+///    application.
+///  * [ExpansionTileTheme] which overrides the default [ExpansionTileTheme]
+///    of its [ExpansionTile] descendants.
+///  * [ThemeData.textTheme], text with a color that contrasts with the card
+///    and canvas colors.
+///  * [ThemeData.colorScheme], the thirteen colors that most Material widget
+///    default colors are based on.
+@immutable
+class ExpansionTileThemeData with Diagnosticable {
+  /// Creates a [ExpansionTileThemeData].
+  const ExpansionTileThemeData ({
+    this.backgroundColor,
+    this.collapsedBackgroundColor,
+    this.tilePadding,
+    this.expandedAlignment,
+    this.childrenPadding,
+    this.iconColor,
+    this.collapsedIconColor,
+    this.textColor,
+    this.collapsedTextColor,
+  });
+
+  /// Overrides the default value of [ExpansionTile.backgroundColor].
+  final Color? backgroundColor;
+
+  /// Overrides the default value of [ExpansionTile.collapsedBackgroundColor].
+  final Color? collapsedBackgroundColor;
+
+  /// Overrides the default value of [ExpansionTile.tilePadding].
+  final EdgeInsetsGeometry? tilePadding;
+
+  /// Overrides the default value of [ExpansionTile.expandedAlignment].
+  final AlignmentGeometry? expandedAlignment;
+
+  /// Overrides the default value of [ExpansionTile.childrenPadding].
+  final EdgeInsetsGeometry? childrenPadding;
+
+  /// Overrides the default value of [ExpansionTile.iconColor].
+  final Color? iconColor;
+
+  /// Overrides the default value of [ExpansionTile.collapsedIconColor].
+  final Color? collapsedIconColor;
+
+  /// Overrides the default value of [ExpansionTile.textColor].
+  final Color? textColor;
+
+  /// Overrides the default value of [ExpansionTile.collapsedTextColor].
+  final Color? collapsedTextColor;
+
+  /// Creates a copy of this object with the given fields replaced with the
+  /// new values.
+  ExpansionTileThemeData copyWith({
+    Color? backgroundColor,
+    Color? collapsedBackgroundColor,
+    EdgeInsetsGeometry? tilePadding,
+    AlignmentGeometry? expandedAlignment,
+    EdgeInsetsGeometry? childrenPadding,
+    Color? iconColor,
+    Color? collapsedIconColor,
+    Color? textColor,
+    Color? collapsedTextColor,
+  }) {
+    return ExpansionTileThemeData(
+      backgroundColor: backgroundColor ?? this.backgroundColor,
+      collapsedBackgroundColor: collapsedBackgroundColor ?? this.collapsedBackgroundColor,
+      tilePadding: tilePadding ?? this.tilePadding,
+      expandedAlignment: expandedAlignment ?? this.expandedAlignment,
+      childrenPadding: childrenPadding ?? this.childrenPadding,
+      iconColor: iconColor ?? this.iconColor,
+      collapsedIconColor: collapsedIconColor ?? this.collapsedIconColor,
+      textColor: textColor ?? this.textColor,
+      collapsedTextColor: collapsedTextColor ?? this.collapsedTextColor,
+    );
+  }
+
+  /// Linearly interpolate between ExpansionTileThemeData objects.
+  static ExpansionTileThemeData? lerp(ExpansionTileThemeData? a, ExpansionTileThemeData? b, double t) {
+    assert (t != null);
+    if (a == null && b == null)
+      return null;
+    return ExpansionTileThemeData(
+      backgroundColor: Color.lerp(a?.backgroundColor, b?.backgroundColor, t),
+      collapsedBackgroundColor: Color.lerp(a?.collapsedBackgroundColor, b?.collapsedBackgroundColor, t),
+      tilePadding: EdgeInsetsGeometry.lerp(a?.tilePadding, b?.tilePadding, t),
+      expandedAlignment: AlignmentGeometry.lerp(a?.expandedAlignment, b?.expandedAlignment, t),
+      childrenPadding: EdgeInsetsGeometry.lerp(a?.childrenPadding, b?.childrenPadding, t),
+      iconColor: Color.lerp(a?.iconColor, b?.iconColor, t),
+      collapsedIconColor: Color.lerp(a?.collapsedIconColor, b?.collapsedIconColor, t),
+      textColor: Color.lerp(a?.textColor, b?.textColor, t),
+      collapsedTextColor: Color.lerp(a?.collapsedTextColor, b?.collapsedTextColor, t),
+    );
+  }
+
+  @override
+  int get hashCode {
+    return hashValues(
+      backgroundColor,
+      collapsedBackgroundColor,
+      tilePadding,
+      expandedAlignment,
+      childrenPadding,
+      iconColor,
+      collapsedIconColor,
+      textColor,
+      collapsedTextColor,
+    );
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (identical(this, other))
+      return true;
+    if (other.runtimeType != runtimeType)
+      return false;
+    return other is ExpansionTileThemeData
+      && other.backgroundColor == backgroundColor
+      && other.collapsedBackgroundColor == collapsedBackgroundColor
+      && other.tilePadding == tilePadding
+      && other.expandedAlignment == expandedAlignment
+      && other.childrenPadding == childrenPadding
+      && other.iconColor == iconColor
+      && other.collapsedIconColor == collapsedIconColor
+      && other.textColor == textColor
+      && other.collapsedTextColor == collapsedTextColor;
+  }
+
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+    super.debugFillProperties(properties);
+    properties.add(ColorProperty('backgroundColor', backgroundColor, defaultValue: null));
+    properties.add(ColorProperty('collapsedBackgroundColor', collapsedBackgroundColor, defaultValue: null));
+    properties.add(DiagnosticsProperty<EdgeInsetsGeometry>('tilePadding', tilePadding, defaultValue: null));
+    properties.add(DiagnosticsProperty<AlignmentGeometry>('expandedAlignment', expandedAlignment, defaultValue: null));
+    properties.add(DiagnosticsProperty<EdgeInsetsGeometry>('childrenPadding', childrenPadding, defaultValue: null));
+    properties.add(ColorProperty('iconColor', iconColor, defaultValue: null));
+    properties.add(ColorProperty('collapsedIconColor', collapsedIconColor, defaultValue: null));
+    properties.add(ColorProperty('textColor', textColor, defaultValue: null));
+    properties.add(ColorProperty('collapsedTextColor', collapsedTextColor, defaultValue: null));
+  }
+}
+
+/// Overrides the default [ExpansionTileTheme] of its [ExpansionTile] descendants.
+///
+/// See also:
+///
+///  * [ExpansionTileThemeData], which is used to configure this theme.
+///  * [ThemeData.expansionTileTheme], which can be used to override the default
+///    [ExpansionTileTheme] for [ExpansionTile]s below the overall [Theme].
+class ExpansionTileTheme extends InheritedTheme {
+  /// Applies the given theme [data] to [child].
+  ///
+  /// The [data] and [child] arguments must not be null.
+  const ExpansionTileTheme({
+    Key? key,
+    required this.data,
+    required Widget child,
+  }) : assert(child != null),
+       assert(data != null),
+       super(key: key, child: child);
+
+  /// Specifies color, alignment, and text style values for
+  /// descendant [ExpansionTile] widgets.
+  final ExpansionTileThemeData data;
+
+  /// The closest instance of this class that encloses the given context.
+  ///
+  /// If there is no enclosing [ExpansionTileTheme] widget, then
+  /// [ThemeData.expansionTileTheme] is used.
+  ///
+  /// Typical usage is as follows:
+  ///
+  /// ```dart
+  /// ExpansionTileThemeData theme = ExpansionTileTheme.of(context);
+  /// ```
+  static ExpansionTileThemeData of(BuildContext context) {
+    final ExpansionTileTheme? inheritedTheme = context.dependOnInheritedWidgetOfExactType<ExpansionTileTheme>();
+    return inheritedTheme?.data ?? Theme.of(context).expansionTileTheme;
+  }
+
+  @override
+  Widget wrap(BuildContext context, Widget child) {
+    return ExpansionTileTheme(data: data, child: child);
+  }
+
+  @override
+  bool updateShouldNotify(ExpansionTileTheme oldWidget) => data != oldWidget.data;
+ }

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

@@ -24,6 +24,7 @@ import 'dialog_theme.dart';
 import 'divider_theme.dart';
 import 'drawer_theme.dart';
 import 'elevated_button_theme.dart';
+import 'expansion_tile_theme.dart';
 import 'floating_action_button_theme.dart';
 import 'ink_splash.dart';
 import 'ink_well.dart' show InteractiveInkFeatureFactory;
@@ -321,6 +322,7 @@ class ThemeData with Diagnosticable {
     TimePickerThemeData? timePickerTheme,
     ToggleButtonsThemeData? toggleButtonsTheme,
     TooltipThemeData? tooltipTheme,
+    ExpansionTileThemeData? expansionTileTheme,
     // DEPRECATED (newest deprecations at the bottom)
     @Deprecated(
       'No longer used by the framework, please remove any reference to it. '
@@ -541,6 +543,7 @@ class ThemeData with Diagnosticable {
     timePickerTheme ??= const TimePickerThemeData();
     toggleButtonsTheme ??= const ToggleButtonsThemeData();
     tooltipTheme ??= const TooltipThemeData();
+    expansionTileTheme ??= const ExpansionTileThemeData();
 
      // DEPRECATED (newest deprecations at the bottom)
     useTextSelectionTheme ??= true;
@@ -630,6 +633,7 @@ class ThemeData with Diagnosticable {
       timePickerTheme: timePickerTheme,
       toggleButtonsTheme: toggleButtonsTheme,
       tooltipTheme: tooltipTheme,
+      expansionTileTheme: expansionTileTheme,
       // DEPRECATED (newest deprecations at the bottom)
       useTextSelectionTheme: useTextSelectionTheme,
       textSelectionColor: textSelectionColor,
@@ -735,6 +739,7 @@ class ThemeData with Diagnosticable {
     required this.timePickerTheme,
     required this.toggleButtonsTheme,
     required this.tooltipTheme,
+    required this.expansionTileTheme,
     // DEPRECATED (newest deprecations at the bottom)
     @Deprecated(
       'No longer used by the framework, please remove any reference to it. '
@@ -873,6 +878,7 @@ class ThemeData with Diagnosticable {
        assert(timePickerTheme != null),
        assert(toggleButtonsTheme != null),
        assert(tooltipTheme != null),
+       assert(expansionTileTheme != null),
         // DEPRECATED (newest deprecations at the bottom)
        assert(useTextSelectionTheme != null),
        assert(textSelectionColor != null),
@@ -1409,6 +1415,9 @@ class ThemeData with Diagnosticable {
   /// This is the value returned from [TooltipTheme.of].
   final TooltipThemeData tooltipTheme;
 
+  /// A theme for customizing the visual properties of [ExpansionTile]s.
+  final ExpansionTileThemeData expansionTileTheme;
+
   // DEPRECATED (newest deprecations at the bottom)
 
   /// A temporary flag that was used to opt-in to the new [TextSelectionTheme]
@@ -1634,6 +1643,7 @@ class ThemeData with Diagnosticable {
     TimePickerThemeData? timePickerTheme,
     ToggleButtonsThemeData? toggleButtonsTheme,
     TooltipThemeData? tooltipTheme,
+    ExpansionTileThemeData? expansionTileTheme,
     // DEPRECATED (newest deprecations at the bottom)
     @Deprecated(
       'No longer used by the framework, please remove any reference to it. '
@@ -1777,6 +1787,7 @@ class ThemeData with Diagnosticable {
       timePickerTheme: timePickerTheme ?? this.timePickerTheme,
       toggleButtonsTheme: toggleButtonsTheme ?? this.toggleButtonsTheme,
       tooltipTheme: tooltipTheme ?? this.tooltipTheme,
+      expansionTileTheme: expansionTileTheme ?? this.expansionTileTheme,
       // DEPRECATED (newest deprecations at the bottom)
       useTextSelectionTheme: useTextSelectionTheme ?? this.useTextSelectionTheme,
       textSelectionColor: textSelectionColor ?? this.textSelectionColor,
@@ -1946,6 +1957,7 @@ class ThemeData with Diagnosticable {
       timePickerTheme: TimePickerThemeData.lerp(a.timePickerTheme, b.timePickerTheme, t),
       toggleButtonsTheme: ToggleButtonsThemeData.lerp(a.toggleButtonsTheme, b.toggleButtonsTheme, t)!,
       tooltipTheme: TooltipThemeData.lerp(a.tooltipTheme, b.tooltipTheme, t)!,
+      expansionTileTheme: ExpansionTileThemeData.lerp(a.expansionTileTheme, b.expansionTileTheme, t)!,
       // DEPRECATED (newest deprecations at the bottom)
       useTextSelectionTheme: t < 0.5 ? a.useTextSelectionTheme : b.useTextSelectionTheme,
       textSelectionColor: Color.lerp(a.textSelectionColor, b.textSelectionColor, t)!,
@@ -2045,6 +2057,7 @@ class ThemeData with Diagnosticable {
         other.timePickerTheme == timePickerTheme &&
         other.toggleButtonsTheme == toggleButtonsTheme &&
         other.tooltipTheme == tooltipTheme &&
+        other.expansionTileTheme == expansionTileTheme &&
         // DEPRECATED (newest deprecations at the bottom)
         other.useTextSelectionTheme == useTextSelectionTheme &&
         other.textSelectionColor == textSelectionColor &&
@@ -2141,6 +2154,7 @@ class ThemeData with Diagnosticable {
       timePickerTheme,
       toggleButtonsTheme,
       tooltipTheme,
+      expansionTileTheme,
       // DEPRECATED (newest deprecations at the bottom)
       useTextSelectionTheme,
       textSelectionColor,
@@ -2237,6 +2251,7 @@ class ThemeData with Diagnosticable {
     properties.add(DiagnosticsProperty<TimePickerThemeData>('timePickerTheme', timePickerTheme, defaultValue: defaultData.timePickerTheme, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<ToggleButtonsThemeData>('toggleButtonsTheme', toggleButtonsTheme, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<TooltipThemeData>('tooltipTheme', tooltipTheme, level: DiagnosticLevel.debug));
+    properties.add(DiagnosticsProperty<ExpansionTileThemeData>('expansionTileTheme', expansionTileTheme, level: DiagnosticLevel.debug));
     // DEPRECATED (newest deprecations at the bottom)
     properties.add(DiagnosticsProperty<bool>('useTextSelectionTheme', useTextSelectionTheme, level: DiagnosticLevel.debug));
     properties.add(ColorProperty('textSelectionColor', textSelectionColor, defaultValue: defaultData.textSelectionColor, level: DiagnosticLevel.debug));

packages/flutter/test/material/expansion_tile_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';
+
+class TestIcon extends StatefulWidget {
+  const TestIcon({Key? key}) : super(key: key);
+
+  @override
+  TestIconState createState() => TestIconState();
+}
+
+class TestIconState extends State<TestIcon> {
+  late IconThemeData iconTheme;
+
+  @override
+  Widget build(BuildContext context) {
+    iconTheme = IconTheme.of(context);
+    return const Icon(Icons.expand_more);
+  }
+}
+class TestText extends StatefulWidget {
+  const TestText(this.text, {Key? key}) : super(key: key);
+
+  final String text;
+
+  @override
+  TestTextState createState() => TestTextState();
+}
+
+class TestTextState extends State<TestText> {
+  late TextStyle textStyle;
+
+  @override
+  Widget build(BuildContext context) {
+    textStyle = DefaultTextStyle.of(context).style;
+    return Text(widget.text);
+  }
+}
+
+void main() {
+  test('ExpansionTileThemeData copyWith, ==, hashCode basics', () {
+    expect(const ExpansionTileThemeData(), const ExpansionTileThemeData().copyWith());
+    expect(const ExpansionTileThemeData().hashCode, const ExpansionTileThemeData().copyWith().hashCode);
+  });
+
+  test('ExpansionTileThemeData defaults', () {
+    const ExpansionTileThemeData theme = ExpansionTileThemeData();
+    expect(theme.backgroundColor, null);
+    expect(theme.collapsedBackgroundColor, null);
+    expect(theme.tilePadding, null);
+    expect(theme.expandedAlignment, null);
+    expect(theme.childrenPadding, null);
+    expect(theme.iconColor, null);
+    expect(theme.collapsedIconColor, null);
+    expect(theme.textColor, null);
+    expect(theme.collapsedTextColor, null);
+  });
+
+  testWidgets('Default ExpansionTileThemeData debugFillProperties', (WidgetTester tester) async {
+    final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
+    const TooltipThemeData().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('ExpansionTileThemeData implements debugFillProperties', (WidgetTester tester) async {
+    final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
+    const ExpansionTileThemeData(
+      backgroundColor: Color(0xff000000),
+      collapsedBackgroundColor: Color(0xff6f83fc),
+      tilePadding: EdgeInsets.all(20.0),
+      expandedAlignment: Alignment.bottomCenter,
+      childrenPadding: EdgeInsets.all(10.0),
+      iconColor: Color(0xffa7c61c),
+      collapsedIconColor: Color(0xffdd0b1f),
+      textColor: Color(0xffffffff),
+      collapsedTextColor: Color(0xff522bab),
+    ).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(0xff000000)',
+      'collapsedBackgroundColor: Color(0xff6f83fc)',
+      'tilePadding: EdgeInsets.all(20.0)',
+      'expandedAlignment: Alignment.bottomCenter',
+      'childrenPadding: EdgeInsets.all(10.0)',
+      'iconColor: Color(0xffa7c61c)',
+      'collapsedIconColor: Color(0xffdd0b1f)',
+      'textColor: Color(0xffffffff)',
+      'collapsedTextColor: Color(0xff522bab)',
+    ]);
+  });
+
+  testWidgets('ExpansionTileTheme - collapsed', (WidgetTester tester) async {
+    final Key tileKey = UniqueKey();
+    final Key titleKey = UniqueKey();
+    final Key iconKey = UniqueKey();
+    const Color backgroundColor = Colors.orange;
+    const Color collapsedBackgroundColor = Colors.red;
+    const Color iconColor = Colors.green;
+    const Color collapsedIconColor = Colors.blue;
+    const Color textColor = Colors.black;
+    const Color collapsedTextColor = Colors.white;
+
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: ThemeData(
+          expansionTileTheme: const ExpansionTileThemeData(
+            backgroundColor: backgroundColor,
+            collapsedBackgroundColor: collapsedBackgroundColor,
+            tilePadding: EdgeInsets.fromLTRB(8, 12, 4, 10),
+            expandedAlignment: Alignment.centerRight,
+            childrenPadding: EdgeInsets.all(20.0),
+            iconColor: iconColor,
+            collapsedIconColor: collapsedIconColor,
+            textColor: textColor,
+            collapsedTextColor: collapsedTextColor,
+          ),
+        ),
+        home: Material(
+          child: Center(
+            child: ExpansionTile(
+              key: tileKey,
+              title: TestText('Collapsed Tile', key: titleKey),
+              trailing: TestIcon(key: iconKey),
+              children: const <Widget>[Text('Tile 1')],
+            ),
+          ),
+        ),
+      ),
+    );
+
+    final BoxDecoration boxDecoration =  tester.firstWidget<Container>(find.descendant(
+      of: find.byKey(tileKey),
+      matching: find.byType(Container),
+    )).decoration! as BoxDecoration;
+    // Check the tile's collapsed background color when collapsedBackgroundColor is applied.
+    expect(boxDecoration.color, collapsedBackgroundColor);
+
+    final Rect titleRect = tester.getRect(find.text('Collapsed Tile'));
+    final Rect trailingRect = tester.getRect(find.byIcon(Icons.expand_more));
+    final Rect listTileRect = tester.getRect(find.byType(ListTile));
+    final Rect tallerWidget = titleRect.height > trailingRect.height ? titleRect : trailingRect;
+
+    // Check the positions of title and trailing Widgets, after padding is applied.
+    expect(listTileRect.left, titleRect.left - 8);
+    expect(listTileRect.right, trailingRect.right + 4);
+
+    // Calculate the remaining height of ListTile from the default height.
+    final double remainingHeight = 56 - tallerWidget.height;
+    expect(listTileRect.top, tallerWidget.top - remainingHeight / 2 - 12);
+    expect(listTileRect.bottom, tallerWidget.bottom + remainingHeight / 2 + 10);
+
+    Color getIconColor() => tester.state<TestIconState>(find.byType(TestIcon)).iconTheme.color!;
+    Color getTextColor() => tester.state<TestTextState>(find.byType(TestText)).textStyle.color!;
+
+    // Check the collapsed icon color when iconColor is applied.
+    expect(getIconColor(), collapsedIconColor);
+    // Check the collapsed text color when textColor is applied.
+    expect(getTextColor(), collapsedTextColor);
+  });
+
+  testWidgets('ExpansionTileTheme - expanded', (WidgetTester tester) async {
+    final Key tileKey = UniqueKey();
+    final Key titleKey = UniqueKey();
+    final Key iconKey = UniqueKey();
+    const Color backgroundColor = Colors.orange;
+    const Color collapsedBackgroundColor = Colors.red;
+    const Color iconColor = Colors.green;
+    const Color collapsedIconColor = Colors.blue;
+    const Color textColor = Colors.black;
+    const Color collapsedTextColor = Colors.white;
+
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: ThemeData(
+          expansionTileTheme: const ExpansionTileThemeData(
+            backgroundColor: backgroundColor,
+            collapsedBackgroundColor: collapsedBackgroundColor,
+            tilePadding: EdgeInsets.fromLTRB(8, 12, 4, 10),
+            expandedAlignment: Alignment.centerRight,
+            childrenPadding: EdgeInsets.all(20.0),
+            iconColor: iconColor,
+            collapsedIconColor: collapsedIconColor,
+            textColor: textColor,
+            collapsedTextColor: collapsedTextColor,
+          ),
+        ),
+        home: Material(
+          child: Center(
+            child: ExpansionTile(
+              key: tileKey,
+              initiallyExpanded: true,
+              title: TestText('Expanded Tile', key: titleKey),
+              trailing: TestIcon(key: iconKey),
+              children: const <Widget>[Text('Tile 1')],
+            ),
+          ),
+        ),
+      ),
+    );
+
+    final BoxDecoration boxDecoration =  tester.firstWidget<Container>(find.descendant(
+      of: find.byKey(tileKey),
+      matching: find.byType(Container),
+    )).decoration! as BoxDecoration;
+    // Check the tile's background color when backgroundColor is applied.
+    expect(boxDecoration.color, backgroundColor);
+
+    final Rect titleRect = tester.getRect(find.text('Expanded Tile'));
+    final Rect trailingRect = tester.getRect(find.byIcon(Icons.expand_more));
+    final Rect listTileRect = tester.getRect(find.byType(ListTile));
+    final Rect tallerWidget = titleRect.height > trailingRect.height ? titleRect : trailingRect;
+
+    // Check the positions of title and trailing Widgets, after padding is applied.
+    expect(listTileRect.left, titleRect.left - 8);
+    expect(listTileRect.right, trailingRect.right + 4);
+
+    // Calculate the remaining height of ListTile from the default height.
+    final double remainingHeight = 56 - tallerWidget.height;
+    expect(listTileRect.top, tallerWidget.top - remainingHeight / 2 - 12);
+    expect(listTileRect.bottom, tallerWidget.bottom + remainingHeight / 2 + 10);
+
+    Color getIconColor() => tester.state<TestIconState>(find.byType(TestIcon)).iconTheme.color!;
+    Color getTextColor() => tester.state<TestTextState>(find.byType(TestText)).textStyle.color!;
+
+    // Check the expanded icon color when iconColor is applied.
+    expect(getIconColor(), iconColor);
+    // Check the expanded text color when textColor is applied.
+    expect(getTextColor(), textColor);
+
+    // Check the child position when expandedAlignment is applied.
+    final Rect childRect = tester.getRect(find.text('Tile 1'));
+    expect(childRect.right, 800 - 20);
+    expect(childRect.left, 800 - childRect.width - 20);
+
+    // Check the child padding when childrenPadding is applied.
+    final Rect paddingRect = tester.getRect(find.byType(Padding).last);
+    expect(childRect.top, paddingRect.top + 20);
+    expect(childRect.left, paddingRect.left + 20);
+    expect(childRect.right, paddingRect.right - 20);
+    expect(childRect.bottom, paddingRect.bottom - 20);
+  });
+}

packages/flutter/test/material/theme_data_test.dart

@@ -430,6 +430,7 @@ void main() {
       sliderTheme: sliderTheme,
       tabBarTheme: const TabBarTheme(labelColor: Colors.black),
       tooltipTheme: const TooltipThemeData(height: 100),
+      expansionTileTheme: const ExpansionTileThemeData(backgroundColor: Colors.black),
       cardTheme: const CardTheme(color: Colors.black),
       chipTheme: chipTheme,
       platform: TargetPlatform.iOS,
@@ -529,6 +530,7 @@ void main() {
       sliderTheme: otherSliderTheme,
       tabBarTheme: const TabBarTheme(labelColor: Colors.white),
       tooltipTheme: const TooltipThemeData(height: 100),
+      expansionTileTheme: const ExpansionTileThemeData(backgroundColor: Colors.black),
       cardTheme: const CardTheme(color: Colors.white),
       chipTheme: otherChipTheme,
       platform: TargetPlatform.android,
@@ -841,6 +843,7 @@ void main() {
       'timePickerTheme',
       'toggleButtonsTheme',
       'tooltipTheme',
+      'expansionTileTheme',
       // DEPRECATED (newest deprecations at the bottom)
       'useTextSelectionTheme',
       'textSelectionColor',