Add CallbackShortcuts example (#123944)

Add CallbackShortcuts example

examples/api/lib/widgets/shortcuts/callback_shortcuts.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';
+import 'package:flutter/services.dart';
+
+/// Flutter code sample for [CallbackShortcuts].
+
+void main() => runApp(const CallbackShortcutsApp());
+
+class CallbackShortcutsApp extends StatelessWidget {
+  const CallbackShortcutsApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      home: Scaffold(
+        appBar: AppBar(title: const Text('CallbackShortcuts Sample')),
+        body: const Center(
+          child: CallbackShortcutsExample(),
+        ),
+      ),
+    );
+  }
+}
+
+class CallbackShortcutsExample extends StatefulWidget {
+  const CallbackShortcutsExample({super.key});
+
+  @override
+  State<CallbackShortcutsExample> createState() => _CallbackShortcutsExampleState();
+}
+
+class _CallbackShortcutsExampleState extends State<CallbackShortcutsExample> {
+  int count = 0;
+
+  @override
+  Widget build(BuildContext context) {
+    return CallbackShortcuts(
+      bindings: <ShortcutActivator, VoidCallback>{
+        const SingleActivator(LogicalKeyboardKey.arrowUp): () {
+          setState(() => count = count + 1);
+        },
+        const SingleActivator(LogicalKeyboardKey.arrowDown): () {
+          setState(() => count = count - 1);
+        },
+      },
+      child: Focus(
+        autofocus: true,
+        child: Column(
+          children: <Widget>[
+            const Text('Press the up arrow key to add to the counter'),
+            const Text('Press the down arrow key to subtract from the counter'),
+            Text('count: $count'),
+          ],
+        ),
+      ),
+    );
+  }
+}

examples/api/test/widgets/shortcuts/callback_shortcuts.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/services.dart';
+import 'package:flutter_api_samples/widgets/shortcuts/callback_shortcuts.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('CallbackShortcutsApp increments and decrements', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.CallbackShortcutsApp(),
+    );
+
+    expect(find.text('count: 0'), findsOneWidget);
+
+    // Increment the counter.
+    await tester.sendKeyEvent(LogicalKeyboardKey.arrowUp);
+    await tester.pump();
+
+    expect(find.text('count: 1'), findsOneWidget);
+
+    // Decrement the counter.
+    await tester.sendKeyEvent(LogicalKeyboardKey.arrowDown);
+    await tester.pump();
+
+    expect(find.text('count: 0'), findsOneWidget);
+  });
+}

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

@@ -1057,6 +1057,13 @@ class _ShortcutsState extends State<Shortcuts> {
 /// deletion intent may be to delete a character in a text input, or to delete
 /// a file in a file menu.
 ///
+/// {@tool dartpad}
+/// This example uses the [CallbackShortcuts] widget to add and subtract
+/// from a counter when the up or down arrow keys are pressed.
+///
+/// ** See code in examples/api/lib/widgets/shortcuts/callback_shortcuts.0.dart **
+/// {@end-tool}
+///
 /// [Shortcuts] and [CallbackShortcuts] can both be used in the same app. As
 /// with any key handling widget, if this widget handles a key event then
 /// widgets above it in the focus chain will not receive the event. This means