[Inspector V2] Fixes an issue where the V2 Inspector wouldn't load af…

…ter hot-restarting from legacy inspector (flutter#8491)

packages/devtools_app/lib/src/screens/inspector_shared/inspector_screen.dart

@@ -3,12 +3,14 @@
 // found in the LICENSE file.
 
 import 'package:devtools_app_shared/shared.dart';
+import 'package:devtools_app_shared/utils.dart';
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 
 import '../../shared/feature_flags.dart';
 import '../../shared/globals.dart';
 import '../../shared/screen.dart';
+import '../../shared/utils.dart';
 import '../inspector/inspector_screen_body.dart' as legacy;
 import '../inspector_v2/inspector_screen_body.dart' as v2;
 import 'inspector_screen_controller.dart';
@@ -33,17 +35,44 @@ class InspectorScreen extends Screen {
       const InspectorScreenSwitcher();
 }
 
-class InspectorScreenSwitcher extends StatelessWidget {
+class InspectorScreenSwitcher extends StatefulWidget {
   const InspectorScreenSwitcher({super.key});
 
+  @override
+  State<InspectorScreenSwitcher> createState() =>
+      _InspectorScreenSwitcherState();
+}
+
+class _InspectorScreenSwitcherState extends State<InspectorScreenSwitcher>
+    with
+        AutoDisposeMixin,
+        ProvidedControllerMixin<InspectorScreenController,
+            InspectorScreenSwitcher> {
+  bool get shouldShowInspectorV2 =>
+      FeatureFlags.inspectorV2 &&
+      preferences.inspector.inspectorV2Enabled.value;
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    if (!initController()) return;
+
+    addAutoDisposeListener(preferences.inspector.inspectorV2Enabled, () async {
+      controller.legacyInspectorController
+          .setVisibleToUser(!shouldShowInspectorV2);
+      await controller.v2InspectorController
+          .setVisibleToUser(shouldShowInspectorV2);
+    });
+  }
+
   @override
   Widget build(BuildContext context) {
     final controller = Provider.of<InspectorScreenController>(context);
 
     return ValueListenableBuilder(
       valueListenable: preferences.inspector.inspectorV2Enabled,
       builder: (context, v2Enabled, _) {
-        if (FeatureFlags.inspectorV2 && v2Enabled) {
+        if (shouldShowInspectorV2) {
           return v2.InspectorScreenBody(
             controller: controller.v2InspectorController,
           );

packages/devtools_app/lib/src/screens/inspector_v2/inspector_controller.dart

@@ -169,7 +169,7 @@ class InspectorController extends DisposableController
       serviceConnection.serviceManager.serviceExtensionManager
           .hasServiceExtension(extensions.toggleSelectWidgetMode.extension);
 
-  void _onClientChange(bool added) {
+  Future<void> _onClientChange(bool added) async {
     if (!added && _clientCount == 0) {
       // Don't try to remove clients if there are none
       return;
@@ -178,10 +178,10 @@ class InspectorController extends DisposableController
     _clientCount += added ? 1 : -1;
     assert(_clientCount >= 0);
     if (_clientCount == 1) {
-      setVisibleToUser(true);
+      await setVisibleToUser(true);
       setActivate(true);
     } else if (_clientCount == 0) {
-      setVisibleToUser(false);
+      await setVisibleToUser(false);
     }
   }
 
@@ -276,13 +276,14 @@ class InspectorController extends DisposableController
     return treeType;
   }
 
-  void setVisibleToUser(bool visible) {
+  Future<void> setVisibleToUser(bool visible) async {
     if (visibleToUser == visible) {
       return;
     }
     visibleToUser = visible;
 
     if (visibleToUser) {
+      await refreshInspector();
     } else {
       shutdownTree(false);
     }

packages/devtools_app/release_notes/NEXT_RELEASE_NOTES.md

@@ -18,6 +18,7 @@ To learn more about DevTools, check out the
 
 - Added an option to the [new Inspector's](https://docs.flutter.dev/tools/devtools/release-notes/release-notes-2.40.1#inspector-updates)
   settings to allow auto-refreshing the widget tree after a hot-reload. - [#8483](https://github.com/flutter/devtools/pull/8483)
+- Fixed an [issue](https://github.com/flutter/devtools/issues/8487) where the [new Inspector](https://docs.flutter.dev/tools/devtools/release-notes/release-notes-2.40.1#inspector-updates) would not load after a hot-restart in the legacy Inspector. - [#8491](https://github.com/flutter/devtools/pull/8491)
 
 ## Performance updates
 

packages/devtools_app/test/inspector_v2/inspector_integration_test.dart

@@ -287,9 +287,7 @@ void main() {
       await tester.pumpAndSettle(inspectorChangeSettleTime);
 
       // Disable Inspector V2:
-      final disableSwitch = find.byType(DevToolsSwitch);
-      expect(disableSwitch, findsOneWidget);
-      await tester.tap(disableSwitch);
+      await toggleV2Inspector(tester);
       await tester.pumpAndSettle(inspectorChangeSettleTime);
 
       // Verify the legacy inspector is visible:
@@ -302,6 +300,43 @@ void main() {
     },
   );
 
+  // Test to verify https://github.com/flutter/devtools/issues/8487 is fixed.
+  testWidgetsWithWindowSize(
+    'revert to legacy inspector, hot-restart, and back to new inspector',
+    windowSize,
+    (WidgetTester tester) async {
+      await _loadInspectorUI(tester);
+
+      // Disable Inspector V2.
+      await toggleV2Inspector(tester);
+      await tester.pumpAndSettle(inspectorChangeSettleTime);
+
+      // Verify the legacy inspector is visible.
+      expect(find.richTextContaining('Widget Details Tree'), findsOneWidget);
+
+      // Trigger a hot restart.
+      await env.flutter!.hotRestart();
+      await tester.pumpAndSettle(inspectorChangeSettleTime);
+
+      // Enable Inspector V2.
+      await toggleV2Inspector(tester);
+      await tester.pumpAndSettle(inspectorChangeSettleTime);
+
+      // Verify the legacy inspector is not visible.
+      expect(find.richTextContaining('Widget Details Tree'), findsNothing);
+
+      // Wait for the widget tree to load.
+      final centerWidgetFinder = find.richText('Center');
+      final centerWidgetFinderWithRetries = await retryUntilFound(
+        centerWidgetFinder,
+        tester: tester,
+        retries: 10,
+      );
+      expect(centerWidgetFinderWithRetries, findsOneWidget);
+    },
+    skip: true, // https://github.com/flutter/devtools/issues/8490
+  );
+
   testWidgetsWithWindowSize(
     'tree nodes contain only essential information',
     windowSize,
@@ -462,6 +497,12 @@ Finder findExpandCollapseButtonForNode({
   return expandCollapseButtonFinder;
 }
 
+Future<void> toggleV2Inspector(WidgetTester tester) async {
+  final inspectorSwitch = find.byType(DevToolsSwitch);
+  expect(inspectorSwitch, findsOneWidget);
+  await tester.tap(inspectorSwitch);
+}
+
 void verifyPropertyIsVisible({
   required String name,
   required String value,