docs: Add more potential use case for Bottom Navigation Bar (#99644)

examples/api/lib/material/bottom_navigation_bar/bottom_navigation_bar.2.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flutter code sample for BottomNavigationBar
+
+import 'package:flutter/material.dart';
+
+void main() => runApp(const MyApp());
+
+class MyApp extends StatelessWidget {
+  const MyApp({super.key});
+
+  static const String _title = 'Flutter Code Sample';
+
+  @override
+  Widget build(BuildContext context) {
+    return const MaterialApp(
+      title: _title,
+      home: MyStatefulWidget(),
+    );
+  }
+}
+
+class MyStatefulWidget extends StatefulWidget {
+  const MyStatefulWidget({super.key});
+
+  @override
+  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
+}
+
+class _MyStatefulWidgetState extends State<MyStatefulWidget> {
+  int _selectedIndex = 0;
+  final ScrollController _homeController = ScrollController();
+
+  Widget _listViewBody() {
+    return ListView.separated(
+        controller: _homeController,
+        itemBuilder: (BuildContext context, int index) {
+          return Center(
+            child: Text(
+              'Item $index',
+            ),
+          );
+        },
+        separatorBuilder: (BuildContext context, int index) => const Divider(
+              thickness: 1,
+            ),
+        itemCount: 50);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('BottomNavigationBar Sample'),
+      ),
+      body: _listViewBody(),
+      bottomNavigationBar: BottomNavigationBar(
+        items: const <BottomNavigationBarItem>[
+          BottomNavigationBarItem(
+            icon: Icon(Icons.home),
+            label: 'Home',
+          ),
+          BottomNavigationBarItem(
+            icon: Icon(Icons.open_in_new_rounded),
+            label: 'Open Dialog',
+          ),
+        ],
+        currentIndex: _selectedIndex,
+        selectedItemColor: Colors.amber[800],
+        onTap: (int index) {
+          switch (index) {
+            case 0:
+              // only scroll to top when current index is selected.
+              if (_selectedIndex == index) {
+                _homeController.animateTo(
+                  0.0,
+                  duration: const Duration(milliseconds: 500),
+                  curve: Curves.easeOut,
+                );
+              }
+              break;
+            case 1:
+              showModal(context);
+              break;
+          }
+          setState(
+            () {
+              _selectedIndex = index;
+            },
+          );
+        },
+      ),
+    );
+  }
+
+  void showModal(BuildContext context) {
+    showDialog(
+      context: context,
+      builder: (BuildContext context) => AlertDialog(
+        content: const Text('Example Dialog'),
+        actions: <TextButton>[
+          TextButton(
+            onPressed: () {
+              Navigator.pop(context);
+            },
+            child: const Text('Close'),
+          )
+        ],
+      ),
+    );
+  }
+}

examples/api/test/material/bottom_navigation_bar/bottom_navigation_bar.2.test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_api_samples/material/bottom_navigation_bar/bottom_navigation_bar.2.dart'
+    as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('BottomNavigationBar Updates Screen Content',
+      (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.MyApp(),
+    );
+
+    expect(find.widgetWithText(AppBar, 'BottomNavigationBar Sample'),
+        findsOneWidget);
+    expect(find.byType(BottomNavigationBar), findsOneWidget);
+    expect(find.widgetWithText(Center, 'Item 0'), findsOneWidget);
+
+    await tester.scrollUntilVisible(
+        find.widgetWithText(Center, 'Item 49'), 100);
+    await tester.pumpAndSettle();
+    expect(find.widgetWithText(Center, 'Item 49'), findsOneWidget);
+
+    await tester.tap(find.byIcon(Icons.home));
+    await tester.tap(find.byIcon(Icons.home));
+    await tester.pumpAndSettle();
+
+    final Scrollable bodyScrollView = tester.widget(find.byType(Scrollable));
+    expect(bodyScrollView.controller?.offset, 0.0);
+
+    await tester.tap(find.byIcon(Icons.open_in_new_rounded));
+    await tester.pumpAndSettle();
+    expect(find.byType(AlertDialog), findsOneWidget);
+  });
+}

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

@@ -118,6 +118,15 @@ enum BottomNavigationBarLandscapeLayout {
 ///
 /// ** See code in examples/api/lib/material/bottom_navigation_bar/bottom_navigation_bar.1.dart **
 /// {@end-tool}
+///
+/// {@tool dartpad}
+/// This example shows [BottomNavigationBar] used in a [Scaffold] Widget with
+/// different interaction patterns. Tapping twice on the first [BottomNavigationBarItem]
+/// uses the [ScrollController] to animate the [ListView] to the top. The second
+/// [BottomNavigationBarItem] shows a Modal Dialog.
+///
+/// ** See code in examples/api/lib/material/bottom_navigation_bar/bottom_navigation_bar.2.dart **
+/// {@end-tool}
 /// See also:
 ///
 ///  * [BottomNavigationBarItem]