Added onEnd callback into AnimatedSize (#139859)

close #106439

Author: feduke-nukem

packages/flutter/lib/src/rendering/animated_size.dart

@@ -82,6 +82,7 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
     super.textDirection,
     super.child,
     Clip clipBehavior = Clip.hardEdge,
+    VoidCallback? onEnd,
   }) : _vsync = vsync,
        _clipBehavior = clipBehavior {
     _controller = AnimationController(
@@ -97,6 +98,7 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
       parent: _controller,
       curve: curve,
     );
+    _onEnd = onEnd;
   }
 
   /// When asserts are enabled, returns the animation controller that is used
@@ -203,6 +205,19 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
     _controller.resync(vsync);
   }
 
+  /// Called every time an animation completes.
+  ///
+  /// This can be useful to trigger additional actions (e.g. another animation)
+  /// at the end of the current animation.
+  VoidCallback? get onEnd => _onEnd;
+  VoidCallback? _onEnd;
+  set onEnd(VoidCallback? value) {
+    if (value == _onEnd) {
+      return;
+    }
+    _onEnd = value;
+  }
+
   @override
   void attach(PipelineOwner owner) {
     super.attach(owner);
@@ -216,11 +231,13 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
         // already, to resume interrupted resizing animation.
         markNeedsLayout();
     }
+    _controller.addStatusListener(_animationStatusListener);
   }
 
   @override
   void detach() {
     _controller.stop();
+    _controller.removeStatusListener(_animationStatusListener);
     super.detach();
   }
 
@@ -363,6 +380,16 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
     }
   }
 
+  void _animationStatusListener(AnimationStatus status) {
+    switch (status) {
+      case AnimationStatus.completed:
+        _onEnd?.call();
+      case AnimationStatus.dismissed:
+      case AnimationStatus.forward:
+      case AnimationStatus.reverse:
+    }
+  }
+
   @override
   void paint(PaintingContext context, Offset offset) {
     if (child != null && _hasVisualOverflow && clipBehavior != Clip.none) {

packages/flutter/lib/src/widgets/animated_size.dart

@@ -31,6 +31,7 @@ class AnimatedSize extends StatefulWidget {
     required this.duration,
     this.reverseDuration,
     this.clipBehavior = Clip.hardEdge,
+    this.onEnd,
   });
 
   /// The widget below this widget in the tree.
@@ -78,6 +79,12 @@ class AnimatedSize extends StatefulWidget {
   /// Defaults to [Clip.hardEdge].
   final Clip clipBehavior;
 
+  /// Called every time an animation completes.
+  ///
+  /// This can be useful to trigger additional actions (e.g. another animation)
+  /// at the end of the current animation.
+  final VoidCallback? onEnd;
+
   @override
   State<AnimatedSize> createState() => _AnimatedSizeState();
 }
@@ -93,6 +100,7 @@ class _AnimatedSizeState
       reverseDuration: widget.reverseDuration,
       vsync: this,
       clipBehavior: widget.clipBehavior,
+      onEnd: widget.onEnd,
       child: widget.child,
     );
   }
@@ -107,6 +115,7 @@ class _AnimatedSize extends SingleChildRenderObjectWidget {
     this.reverseDuration,
     required this.vsync,
     this.clipBehavior = Clip.hardEdge,
+    this.onEnd,
   });
 
   final AlignmentGeometry alignment;
@@ -119,6 +128,8 @@ class _AnimatedSize extends SingleChildRenderObjectWidget {
 
   final Clip clipBehavior;
 
+  final VoidCallback? onEnd;
+
   @override
   RenderAnimatedSize createRenderObject(BuildContext context) {
     return RenderAnimatedSize(
@@ -129,6 +140,7 @@ class _AnimatedSize extends SingleChildRenderObjectWidget {
       vsync: vsync,
       textDirection: Directionality.maybeOf(context),
       clipBehavior: clipBehavior,
+      onEnd: onEnd,
     );
   }
 
@@ -141,7 +153,8 @@ class _AnimatedSize extends SingleChildRenderObjectWidget {
       ..curve = curve
       ..vsync = vsync
       ..textDirection = Directionality.maybeOf(context)
-      ..clipBehavior = clipBehavior;
+      ..clipBehavior = clipBehavior
+      ..onEnd = onEnd;
   }
 
   @override

packages/flutter/test/widgets/animated_size_test.dart

@@ -87,6 +87,61 @@ void main() {
       expect(box.size.height, equals(100.0));
     });
 
+    testWidgets('calls onEnd when animation is completed', (WidgetTester tester) async {
+      int callCount = 0;
+      void handleEnd() {
+        callCount++;
+      }
+
+      await tester.pumpWidget(
+        Center(
+          child: AnimatedSize(
+            onEnd: handleEnd,
+            duration: const Duration(milliseconds: 200),
+            child: const SizedBox(
+              width: 100.0,
+              height: 100.0,
+            ),
+          ),
+        ),
+      );
+
+      expect(callCount, equals(0));
+
+      await tester.pumpWidget(
+        Center(
+          child: AnimatedSize(
+            onEnd: handleEnd,
+            duration: const Duration(milliseconds: 200),
+            child: const SizedBox(
+              width: 200.0,
+              height: 200.0,
+            ),
+          ),
+        ),
+      );
+
+      expect(callCount, equals(0));
+      await tester.pumpAndSettle();
+      expect(callCount, equals(1));
+
+      await tester.pumpWidget(
+        Center(
+          child: AnimatedSize(
+            onEnd: handleEnd,
+            duration: const Duration(milliseconds: 200),
+            child: const SizedBox(
+              width: 100.0,
+              height: 100.0,
+            ),
+          ),
+        ),
+      );
+
+      await tester.pumpAndSettle();
+      expect(callCount, equals(2));
+    });
+
     testWidgets('clamps animated size to constraints', (WidgetTester tester) async {
       await tester.pumpWidget(
         const Center(