From d85571b46bc159882bb251fd5af195ffa4042f93 Mon Sep 17 00:00:00 2001
From: Chikamatsu Kazuya <43089218+chika3742@users.noreply.github.com>
Date: Thu, 25 Apr 2024 07:44:04 +0900
Subject: [PATCH] Add support for overriding `reverseCurve` with
 `ExpansionTile.expansionAnimationStyle` (#147103)

This PR adds support for overriding `reverseCurve` with `ExpansionTile.expansionAnimationStyle`.

Closes #146760
---
 .../lib/src/material/expansion_tile.dart      | 18 ++++++++++++++----
 .../test/material/expansion_tile_test.dart    | 19 +++++++++++++++++--
 2 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/packages/flutter/lib/src/material/expansion_tile.dart b/packages/flutter/lib/src/material/expansion_tile.dart
index fab75cba946..6cd45acce55 100644
--- a/packages/flutter/lib/src/material/expansion_tile.dart
+++ b/packages/flutter/lib/src/material/expansion_tile.dart
@@ -543,6 +543,11 @@ class ExpansionTile extends StatefulWidget {
   /// from the [ExpansionTileThemeData.expansionAnimationStyle] will be used.
   /// Otherwise, defaults to [Curves.easeIn].
   ///
+  /// If [AnimationStyle.reverseCurve] is provided, it will be used to override
+  /// the collapse animation curve. If it is null, then [AnimationStyle.reverseCurve]
+  /// from the [ExpansionTileThemeData.expansionAnimationStyle] will be used.
+  /// Otherwise, the same curve will be used as for expansion.
+  ///
   /// To disable the theme animation, use [AnimationStyle.noAnimation].
   ///
   /// {@tool dartpad}
@@ -566,11 +571,11 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
   final ColorTween _headerColorTween = ColorTween();
   final ColorTween _iconColorTween = ColorTween();
   final ColorTween _backgroundColorTween = ColorTween();
-  final CurveTween _heightFactorTween = CurveTween(curve: Curves.easeIn);
+  final Tween<double> _heightFactorTween = Tween<double>(begin: 0.0, end: 1.0);
 
   late AnimationController _animationController;
   late Animation<double> _iconTurns;
-  late Animation<double> _heightFactor;
+  late CurvedAnimation _heightFactor;
   late Animation<ShapeBorder?> _border;
   late Animation<Color?> _headerColor;
   late Animation<Color?> _iconColor;
@@ -584,7 +589,10 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
   void initState() {
     super.initState();
     _animationController = AnimationController(duration: _kExpand, vsync: this);
-    _heightFactor = _animationController.drive(_heightFactorTween);
+    _heightFactor = CurvedAnimation(
+      parent: _animationController.drive(_heightFactorTween),
+      curve: Curves.easeIn,
+    );
     _iconTurns = _animationController.drive(_halfTween.chain(_easeInTween));
     _border = _animationController.drive(_borderTween.chain(_easeOutTween));
     _headerColor = _animationController.drive(_headerColorTween.chain(_easeInTween));
@@ -862,9 +870,11 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
   }
 
   void _updateHeightFactorCurve(ExpansionTileThemeData expansionTileTheme) {
-    _heightFactorTween.curve = widget.expansionAnimationStyle?.curve
+    _heightFactor.curve = widget.expansionAnimationStyle?.curve
       ?? expansionTileTheme.expansionAnimationStyle?.curve
       ?? Curves.easeIn;
+    _heightFactor.reverseCurve = widget.expansionAnimationStyle?.reverseCurve
+      ?? expansionTileTheme.expansionAnimationStyle?.reverseCurve;
   }
 
   @override
diff --git a/packages/flutter/test/material/expansion_tile_test.dart b/packages/flutter/test/material/expansion_tile_test.dart
index 536e4fd36ae..70daebbb82f 100644
--- a/packages/flutter/test/material/expansion_tile_test.dart
+++ b/packages/flutter/test/material/expansion_tile_test.dart
@@ -1149,7 +1149,10 @@ void main() {
     await tester.pumpAndSettle();
 
     // Override the animation curve.
-    await tester.pumpWidget(buildExpansionTile(animationStyle: AnimationStyle(curve: Easing.emphasizedDecelerate)));
+    await tester.pumpWidget(buildExpansionTile(animationStyle: AnimationStyle(
+      curve: Easing.emphasizedDecelerate,
+      reverseCurve: Easing.emphasizedAccelerate,
+    )));
     await tester.pumpAndSettle();
 
     // Test the overridden animation curve.
@@ -1167,8 +1170,20 @@ void main() {
 
     expect(getHeight(expansionTileKey), 158.0);
 
-    // Tap to collapse the ExpansionTile.
+    // Test the overridden reverse (collapse) animation curve.
     await tester.tap(find.text('title'));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 50)); // Advance the animation by 1/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(98.6, 0.1));
+
+    await tester.pump(const Duration(milliseconds: 50)); // Advance the animation by 2/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(73.4, 0.1));
+
+    await tester.pumpAndSettle(); // Advance the animation to the end.
+
+    expect(getHeight(expansionTileKey), 58.0);
 
     // Test no animation.
     await tester.pumpWidget(buildExpansionTile(animationStyle: AnimationStyle.noAnimation));