Add missing example links (#130521)

## Description

This adds some more missing example links.

I also wrote another PR for adding a check to make sure that examples are all linked from a source file and have tests: https://github.com/flutter/flutter/pull/130523

## Related Issues
 - https://github.com/flutter/flutter/issues/129956

## Tests
 - Documentation and refactoring only.

examples/api/lib/material/drawer/drawer.0.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';
+
+/// Flutter code sample for [Drawer].
+
+void main() => runApp(const DrawerApp());
+
+class DrawerApp extends StatelessWidget {
+  const DrawerApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      theme: ThemeData(useMaterial3: true),
+      home: const DrawerExample(),
+    );
+  }
+}
+
+class DrawerExample extends StatefulWidget {
+  const DrawerExample({super.key});
+
+  @override
+  State<DrawerExample> createState() => _DrawerExampleState();
+}
+
+class _DrawerExampleState extends State<DrawerExample> {
+  String selectedPage = '';
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Drawer Example'),
+      ),
+      drawer: Drawer(
+        child: ListView(
+          padding: EdgeInsets.zero,
+          children: <Widget>[
+            const DrawerHeader(
+              decoration: BoxDecoration(
+                color: Colors.blue,
+              ),
+              child: Text(
+                'Drawer Header',
+                style: TextStyle(
+                  color: Colors.white,
+                  fontSize: 24,
+                ),
+              ),
+            ),
+            ListTile(
+              leading: const Icon(Icons.message),
+              title: const Text('Messages'),
+              onTap: () {
+                setState(() {
+                  selectedPage = 'Messages';
+                });
+              },
+            ),
+            ListTile(
+              leading: const Icon(Icons.account_circle),
+              title: const Text('Profile'),
+              onTap: () {
+                setState(() {
+                  selectedPage = 'Profile';
+                });
+              },
+            ),
+            ListTile(
+              leading: const Icon(Icons.settings),
+              title: const Text('Settings'),
+              onTap: () {
+                setState(() {
+                  selectedPage = 'Settings';
+                });
+              },
+            ),
+          ],
+        ),
+      ),
+      body: Center(
+        child: Text('Page: $selectedPage'),
+      ),
+    );
+  }
+}

examples/api/lib/material/navigation_drawer/navigation_drawer.0.dart

@@ -11,6 +11,8 @@ import 'package:flutter/material.dart';
 
 /// Flutter code sample for [NavigationDrawer].
 
+void main() => runApp(const NavigationDrawerApp());
+
 class ExampleDestination {
   const ExampleDestination(this.label, this.icon, this.selectedIcon);
 
@@ -20,20 +22,22 @@ class ExampleDestination {
 }
 
 const List<ExampleDestination> destinations = <ExampleDestination>[
-  ExampleDestination('page 0', Icon(Icons.widgets_outlined), Icon(Icons.widgets)),
-  ExampleDestination('page 1', Icon(Icons.format_paint_outlined), Icon(Icons.format_paint)),
-  ExampleDestination('page 2', Icon(Icons.text_snippet_outlined), Icon(Icons.text_snippet)),
-  ExampleDestination('page 3', Icon(Icons.invert_colors_on_outlined), Icon(Icons.opacity)),
+  ExampleDestination('Messages', Icon(Icons.widgets_outlined), Icon(Icons.widgets)),
+  ExampleDestination('Profile', Icon(Icons.format_paint_outlined), Icon(Icons.format_paint)),
+  ExampleDestination('Settings', Icon(Icons.settings_outlined), Icon(Icons.settings)),
 ];
 
-void main() {
-  runApp(
-    MaterialApp(
+class NavigationDrawerApp extends StatelessWidget {
+  const NavigationDrawerApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
       debugShowCheckedModeBanner: false,
       theme: ThemeData(useMaterial3: true),
       home: const NavigationDrawerExample(),
-    ),
-  );
+    );
+  }
 }
 
 class NavigationDrawerExample extends StatefulWidget {
@@ -65,7 +69,7 @@ class _NavigationDrawerExampleState extends State<NavigationDrawerExample> {
         child: Column(
           mainAxisAlignment: MainAxisAlignment.spaceEvenly,
           children: <Widget>[
-            Text('Page Index =  $screenIndex'),
+            Text('Page Index = $screenIndex'),
           ],
         ),
       ),
@@ -125,7 +129,7 @@ class _NavigationDrawerExampleState extends State<NavigationDrawerExample> {
               child: Column(
                 mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                 children: <Widget>[
-                  Text('Page Index =  $screenIndex'),
+                  Text('Page Index = $screenIndex'),
                   ElevatedButton(
                     onPressed: openDrawer,
                     child: const Text('Open Drawer'),

examples/api/lib/material/navigation_drawer/navigation_drawer.1.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';
-
-/// Flutter code sample for [NavigationDrawer].
-
-void main() => runApp(const MyApp());
-
-class MyApp extends StatelessWidget {
-  const MyApp({super.key});
-
-  @override
-  Widget build(BuildContext context) {
-    return MaterialApp(
-      title: 'Flutter Demo',
-      debugShowCheckedModeBanner: false,
-      theme: ThemeData(
-        useMaterial3: true,
-      ),
-      home:  const MyHomePage(),
-    );
-  }
-}
-
-class MyHomePage extends StatelessWidget {
-  const MyHomePage({super.key});
-
-  @override
-  Widget build(BuildContext context) {
-    return Scaffold(
-      appBar: AppBar(
-        title: const Text('Drawer Demo'),
-      ),
-      drawer: NavigationDrawer(
-        children: <Widget>[
-          Padding(
-                padding: const EdgeInsets.fromLTRB(28, 16, 16, 10),
-                child: Text(
-                  'Drawer Header',
-                  style: Theme.of(context).textTheme.titleSmall,
-                ),
-              ),
-          const NavigationDrawerDestination(
-            icon: Icon(Icons.message),
-            label: Text('Messages'),
-          ),
-          const NavigationDrawerDestination(
-            icon: Icon(Icons.account_circle),
-            label: Text('Profile'),
-          ),
-          const NavigationDrawerDestination(
-            icon: Icon(Icons.settings),
-            label: Text('Settings'),
-          ),
-        ])
-    );
-  }
-}

examples/api/lib/material/scaffold/scaffold_state.show_snack_bar.0.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';
-
-/// Flutter code sample for [ScaffoldState.showSnackBar].
-
-void main() => runApp(const ShowSnackBarExampleApp());
-
-class ShowSnackBarExampleApp extends StatelessWidget {
-  const ShowSnackBarExampleApp({super.key});
-
-  @override
-  Widget build(BuildContext context) {
-    return MaterialApp(
-      home: Scaffold(
-        appBar: AppBar(title: const Text('ScaffoldState Sample')),
-        body: const Center(
-          child: ShowSnackBarExample(),
-        ),
-      ),
-    );
-  }
-}
-
-class ShowSnackBarExample extends StatelessWidget {
-  const ShowSnackBarExample({super.key});
-
-  @override
-  Widget build(BuildContext context) {
-    return OutlinedButton(
-      onPressed: () {
-        ScaffoldMessenger.of(context).showSnackBar(
-          const SnackBar(
-            content: Text('A SnackBar has been shown.'),
-          ),
-        );
-      },
-      child: const Text('Show SnackBar'),
-    );
-  }
-}

examples/api/test/material/drawer/drawer.0_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/drawer/drawer.0.dart'
+    as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Navigation bar updates destination on tap',
+      (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.DrawerApp(),
+    );
+
+    await tester.tap(find.byIcon(Icons.menu));
+    await tester.pumpAndSettle();
+
+    /// NavigationDestinations must be rendered
+    expect(find.text('Messages'), findsOneWidget);
+    expect(find.text('Profile'), findsOneWidget);
+    expect(find.text('Settings'), findsOneWidget);
+
+    /// Initial index must be zero
+    expect(find.text('Page: '), findsOneWidget);
+
+    /// Switch to second tab
+    await tester.tap(find.ancestor(of: find.text('Messages'), matching: find.byType(InkWell)));
+    await tester.pumpAndSettle();
+    expect(find.text('Page: Messages'), findsOneWidget);
+
+    /// Switch to third tab
+    await tester.tap(find.ancestor(of: find.text('Profile'), matching: find.byType(InkWell)));
+    await tester.pumpAndSettle();
+    expect(find.text('Page: Profile'), findsOneWidget);
+
+    /// Switch to fourth tab
+    await tester.tap(find.ancestor(of: find.text('Settings'), matching: find.byType(InkWell)));
+    await tester.pumpAndSettle();
+    expect(find.text('Page: Settings'), findsOneWidget);
+  });
+}

examples/api/test/material/navigation_drawer/navigation_drawer.0_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/navigation_drawer/navigation_drawer.0.dart'
+    as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Navigation bar updates destination on tap',
+      (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.NavigationDrawerApp(),
+    );
+
+    await tester.tap(find.text('Open Drawer'));
+    await tester.pumpAndSettle();
+
+    final NavigationDrawer navigationDrawerWidget = tester.firstWidget(find.byType(NavigationDrawer));
+
+    /// NavigationDestinations must be rendered
+    expect(find.text('Messages'), findsNWidgets(2));
+    expect(find.text('Profile'), findsNWidgets(2));
+    expect(find.text('Settings'), findsNWidgets(2));
+
+    /// Initial index must be zero
+    expect(navigationDrawerWidget.selectedIndex, 0);
+    expect(find.text('Page Index = 0'), findsOneWidget);
+
+    /// Switch to second tab
+    await tester.tap(find.ancestor(of: find.text('Profile'), matching: find.byType(InkWell)));
+    await tester.pumpAndSettle();
+    expect(find.text('Page Index = 1'), findsOneWidget);
+
+    /// Switch to fourth tab
+    await tester.tap(find.ancestor(of: find.text('Settings'), matching: find.byType(InkWell)));
+    await tester.pumpAndSettle();
+    expect(find.text('Page Index = 2'), findsOneWidget);
+  });
+}