Fix a memory leak in AutomaticKeepAlive (#124163)

Fix a memory leak in `AutomaticKeepAlive`

Author: GregoryConrad

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

@@ -144,7 +144,8 @@ class _AutomaticKeepAliveState extends State<AutomaticKeepAlive> {
   }
 
   VoidCallback _createCallback(Listenable handle) {
-    return () {
+    late final VoidCallback callback;
+    return callback = () {
       assert(() {
         if (!mounted) {
           throw FlutterError(
@@ -157,6 +158,7 @@ class _AutomaticKeepAliveState extends State<AutomaticKeepAlive> {
         return true;
       }());
       _handles!.remove(handle);
+      handle.removeListener(callback);
       if (_handles!.isEmpty) {
         if (SchedulerBinding.instance.schedulerPhase.index < SchedulerPhase.persistentCallbacks.index) {
           // Build/layout haven't started yet so let's just schedule this for

packages/flutter/test/widgets/automatic_keep_alive_test.dart

@@ -557,6 +557,26 @@ void main() {
 
     expect(alternate.children.length, 1);
   });
+
+  testWidgets('Keep alive Listenable has its listener removed once called', (WidgetTester tester) async {
+    final LeakCheckerHandle handle = LeakCheckerHandle();
+    await tester.pumpWidget(Directionality(
+      textDirection: TextDirection.ltr,
+      child: ListView.builder(
+        itemCount: 1,
+        itemBuilder: (BuildContext context, int index) {
+          return const KeepAliveListenableLeakChecker(key: GlobalObjectKey<_KeepAliveListenableLeakCheckerState>(0));
+        },
+      ),
+    ));
+    final _KeepAliveListenableLeakCheckerState state = const GlobalObjectKey<_KeepAliveListenableLeakCheckerState>(0).currentState!;
+
+    expect(handle.hasListeners, false);
+    state.dispatch(handle);
+    expect(handle.hasListeners, true);
+    handle.notifyListeners();
+    expect(handle.hasListeners, false);
+  });
 }
 
 class _AlwaysKeepAlive extends StatefulWidget {
@@ -633,3 +653,26 @@ class RenderSliverMultiBoxAdaptorAlt extends RenderSliver with
   @override
   void performLayout() { }
 }
+
+class LeakCheckerHandle with ChangeNotifier {
+  @override
+  bool get hasListeners => super.hasListeners;
+}
+
+class KeepAliveListenableLeakChecker extends StatefulWidget {
+  const KeepAliveListenableLeakChecker({super.key});
+
+  @override
+  State<KeepAliveListenableLeakChecker> createState() => _KeepAliveListenableLeakCheckerState();
+}
+
+class _KeepAliveListenableLeakCheckerState extends State<KeepAliveListenableLeakChecker> {
+  void dispatch(Listenable handle) {
+    KeepAliveNotification(handle).dispatch(context);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return const Placeholder();
+  }
+}