issue 61346 route can be added and disposed in the same frame (flutte…

…r#61375)

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

@@ -213,7 +213,11 @@ abstract class Route<T> {
     // focused child can only be attached to navigator after initState which
     // will be guarded by the asynchronous gap.
     TickerFuture.complete().then<void>((void _) {
-      navigator.focusScopeNode.requestFocus();
+      // The route can be disposed before the ticker future completes. This can
+      // happen when the navigator is under a TabView that does a warping. The
+      // navigator will be null in this case, and we have to do a null-safe
+      // operation.
+      navigator?.focusScopeNode?.requestFocus();
     });
   }
 

packages/flutter/test/widgets/navigator_test.dart

@@ -489,6 +489,38 @@ void main() {
     expect(observations[2].previous, '/A');
   });
 
+  testWidgets('Route didAdd and dispose in same frame work', (WidgetTester tester) async {
+    // Regression Test for https://github.com/flutter/flutter/issues/61346.
+    Widget buildNavigator() {
+      return Navigator(
+        pages: <Page<void>>[
+          MaterialPage<void>(
+            builder: (BuildContext context) => const Placeholder(),
+          )
+        ],
+        onPopPage: (Route<dynamic> route, dynamic result) => false,
+      );
+    }
+    final TabController controller = TabController(length: 3, vsync: tester);
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: TabBarView(
+          controller: controller,
+          children: <Widget>[
+            buildNavigator(),
+            buildNavigator(),
+            buildNavigator(),
+          ],
+        )
+      ),
+    );
+
+    // This test should finish without crashing.
+    controller.index = 2;
+    await tester.pumpAndSettle();
+  });
+
   testWidgets('replaceNamed replaces', (WidgetTester tester) async {
     final Map<String, WidgetBuilder> routes = <String, WidgetBuilder>{
       '/' : (BuildContext context) => OnTapPage(id: '/', onTap: () { Navigator.pushReplacementNamed(context, '/A'); }),