fix some DSS bugs (#112142)

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

@@ -201,8 +201,12 @@ class DraggableScrollableController extends ChangeNotifier {
     }
   }
 
-  void _detach() {
-    _attachedController?.extent._currentSize.removeListener(notifyListeners);
+  void _detach({bool disposeExtent = false}) {
+    if (disposeExtent) {
+      _attachedController?.extent.dispose();
+    } else {
+      _attachedController?.extent._currentSize.removeListener(notifyListeners);
+    }
     _attachedController = null;
   }
 
@@ -593,6 +597,10 @@ class _DraggableSheetExtent {
     return size / maxSize * availablePixels;
   }
 
+  void dispose() {
+    _currentSize.dispose();
+  }
+
   _DraggableSheetExtent copyWith({
     required double minSize,
     required double maxSize,
@@ -663,6 +671,10 @@ class _DraggableScrollableSheetState extends State<DraggableScrollableSheet> {
   @override
   void didUpdateWidget(covariant DraggableScrollableSheet oldWidget) {
     super.didUpdateWidget(oldWidget);
+    if (widget.controller != oldWidget.controller) {
+      oldWidget.controller?._detach();
+      widget.controller?._attach(_scrollController);
+    }
     _replaceExtent(oldWidget);
   }
 
@@ -695,14 +707,14 @@ class _DraggableScrollableSheetState extends State<DraggableScrollableSheet> {
 
   @override
   void dispose() {
-    widget.controller?._detach();
+    widget.controller?._detach(disposeExtent: true);
     _scrollController.dispose();
     super.dispose();
   }
 
   void _replaceExtent(covariant DraggableScrollableSheet oldWidget) {
     final _DraggableSheetExtent previousExtent = _extent;
-    _extent = _extent.copyWith(
+    _extent = previousExtent.copyWith(
       minSize: widget.minChildSize,
       maxSize: widget.maxChildSize,
       snap: widget.snap,
@@ -716,6 +728,7 @@ class _DraggableScrollableSheetState extends State<DraggableScrollableSheet> {
     // If an external facing controller was provided, let it know that the
     // extent has been replaced.
     widget.controller?._onExtentReplaced(previousExtent);
+    previousExtent.dispose();
     if (widget.snap
         && (widget.snap != oldWidget.snap || widget.snapSizes != oldWidget.snapSizes)
         && _scrollController.hasClients

packages/flutter/test/widgets/draggable_scrollable_sheet_test.dart

@@ -1512,4 +1512,62 @@ void main() {
     // DraggableScrollableSheet has rebuilt, so expect the builder to be called.
     expect(buildCount, 2);
   });
+
+  testWidgets('DraggableScrollableSheet controller can be changed', (WidgetTester tester) async {
+    final DraggableScrollableController controller1 = DraggableScrollableController();
+    final DraggableScrollableController controller2 = DraggableScrollableController();
+    final List<double> loggedSizes = <double>[];
+
+    DraggableScrollableController controller = controller1;
+    await tester.pumpWidget(MaterialApp(
+      home: StatefulBuilder(
+        builder: (BuildContext context, StateSetter setState) => Scaffold(
+          body: DraggableScrollableSheet(
+            initialChildSize: 0.25,
+            snap: true,
+            snapSizes: const <double>[0.25, 0.5, 1.0],
+            controller: controller,
+            builder: (BuildContext context, ScrollController scrollController) {
+              return ListView(
+                controller: scrollController,
+                children: <Widget>[
+                  ElevatedButton(
+                    onPressed: () => setState(() {
+                      controller = controller2;
+                    }),
+                    child: const Text('Switch controller'),
+                  ),
+                  Container(
+                    height: 10000,
+                    color: Colors.blue,
+                  ),
+                ],
+              );
+            },
+          ),
+        ),
+      ),
+    ));
+    expect(controller1.isAttached, true);
+    expect(controller2.isAttached, false);
+
+    controller1.addListener(() {
+      loggedSizes.add(controller1.size);
+    });
+    controller1.jumpTo(0.5);
+    expect(loggedSizes, <double>[0.5].map((double v) => closeTo(v, precisionErrorTolerance)));
+    loggedSizes.clear();
+
+    await tester.tap(find.text('Switch controller'));
+    await tester.pump();
+
+    expect(controller1.isAttached, false);
+    expect(controller2.isAttached, true);
+
+    controller2.addListener(() {
+      loggedSizes.add(controller2.size);
+    });
+    controller2.jumpTo(1.0);
+    expect(loggedSizes, <double>[1.0].map((double v) => closeTo(v, precisionErrorTolerance)));
+  });
 }