Improve the Scaffold.bottomSheet update behavior (#73084)

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

@@ -2389,6 +2389,7 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin, Resto
   // bottom sheet.
   final List<_StandardBottomSheet> _dismissedBottomSheets = <_StandardBottomSheet>[];
   PersistentBottomSheetController<dynamic>? _currentBottomSheet;
+  final GlobalKey _currentBottomSheetKey = GlobalKey();
 
   void _maybeBuildPersistentBottomSheet() {
     if (widget.bottomSheet != null && _currentBottomSheet == null) {
@@ -2421,7 +2422,10 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin, Resto
           return NotificationListener<DraggableScrollableNotification>(
             onNotification: _persistentBottomSheetExtentChanged,
             child: DraggableScrollableActuator(
-              child: widget.bottomSheet!,
+              child: StatefulBuilder(
+                key: _currentBottomSheetKey,
+                builder: (BuildContext context, StateSetter setState) => widget.bottomSheet!,
+              ),
             ),
           );
         },
@@ -2445,6 +2449,10 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin, Resto
     }
   }
 
+  void _updatePersistentBottomSheet() {
+    _currentBottomSheetKey.currentState!.setState(() {});
+  }
+
   PersistentBottomSheetController<T> _buildBottomSheet<T>(
     WidgetBuilder builder,
     bool isPersistent, {
@@ -2774,8 +2782,13 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin, Resto
         }
         return true;
       }());
-      _closeCurrentBottomSheet();
-      _maybeBuildPersistentBottomSheet();
+      if (widget.bottomSheet == null) {
+        _closeCurrentBottomSheet();
+      } else if (widget.bottomSheet != null && oldWidget.bottomSheet == null) {
+        _maybeBuildPersistentBottomSheet();
+      } else {
+        _updatePersistentBottomSheet();
+      }
     }
     super.didUpdateWidget(oldWidget);
   }

packages/flutter/test/material/persistent_bottom_sheet_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
 
 void main() {
   // Pumps and ensures that the BottomSheet animates non-linearly.
@@ -475,6 +476,28 @@ void main() {
     expect(find.byKey(bottomSheetKey), findsNothing);
   });
 
+  // Regression test for https://github.com/flutter/flutter/issues/71435
+  testWidgets('Scaffold.bottomSheet should be updated without creating a new RO'
+      ' when the new widget has the same key and type.', (WidgetTester tester) async {
+    Widget buildFrame(String text) {
+      return MaterialApp(
+        home: Scaffold(
+          body: const Placeholder(),
+          bottomSheet: Text(text),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildFrame('I love Flutter!'));
+    final RenderParagraph renderBeforeUpdate = tester.renderObject(find.text('I love Flutter!'));
+
+    await tester.pumpWidget(buildFrame('Flutter is the best!'));
+    await tester.pumpAndSettle();
+    final RenderParagraph renderAfterUpdate = tester.renderObject(find.text('Flutter is the best!'));
+
+    expect(renderBeforeUpdate, renderAfterUpdate);
+  });
+
   testWidgets('Verify that visual properties are passed through', (WidgetTester tester) async {
     final GlobalKey<ScaffoldState> scaffoldKey = GlobalKey<ScaffoldState>();
     const Color color = Colors.pink;