Add `CupertinoSlider` example (#93633)

examples/api/lib/cupertino/slider/cupertino_slider.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.
+
+// Flutter code sample for CupertinoSlider
+
+import 'package:flutter/cupertino.dart';
+
+void main() => runApp(const MyApp());
+
+class MyApp extends StatelessWidget {
+  const MyApp({Key? key}) : super(key: key);
+
+  static const String _title = 'Flutter Code Sample';
+
+  @override
+  Widget build(BuildContext context) {
+    return const CupertinoApp(
+      title: _title,
+      home: CupertinoSliderSample(),
+    );
+  }
+}
+
+class CupertinoSliderSample extends StatefulWidget {
+  const CupertinoSliderSample({Key? key}) : super(key: key);
+
+  @override
+  State<CupertinoSliderSample> createState() => _CupertinoSliderSampleState();
+}
+
+class _CupertinoSliderSampleState extends State<CupertinoSliderSample> {
+  double _currentSliderValue =  0.0;
+  String? _sliderStatus;
+
+  @override
+  Widget build(BuildContext context) {
+    return CupertinoPageScaffold(
+      child: Center(
+        child: Column(
+          mainAxisSize: MainAxisSize.min,
+          children: <Widget>[
+            // Display the current slider value.
+            Text('$_currentSliderValue'),
+            CupertinoSlider(
+              key: const Key('slider'),
+              value: _currentSliderValue,
+              // This allows the slider to jump between divisions.
+              // If null, the slide movement is continuous.
+              divisions: 5,
+              // The maximum slider value
+              max: 100,
+              activeColor: CupertinoColors.systemPurple,
+              thumbColor: CupertinoColors.systemPurple,
+              // This is called when sliding is started.
+              onChangeStart: (double value) {
+                setState(() {
+                  _sliderStatus = 'Sliding';
+                });
+              },
+              // This is called when sliding has ended.
+              onChangeEnd: (double value) {
+                setState(() {
+                  _sliderStatus = 'Finished sliding';
+                });
+              },
+              // This is called when slider value is changed.
+              onChanged: (double value) {
+                setState(() {
+                  _currentSliderValue = value;
+                });
+              },
+            ),
+            Text(
+              _sliderStatus ?? '',
+              style: CupertinoTheme.of(context).textTheme.textStyle.copyWith(
+                fontSize: 12,
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

examples/api/test/cupertino/slider/cupertino_slider.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/cupertino.dart';
+import 'package:flutter_api_samples/cupertino/slider/cupertino_slider.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  Future<void> _dragSlider(WidgetTester tester, Key sliderKey) {
+    final Offset topLeft = tester.getTopLeft(find.byKey(sliderKey));
+    const double unit = CupertinoThumbPainter.radius;
+    const double delta = 3.0 * unit;
+    return tester.dragFrom(topLeft + const Offset(unit, unit), const Offset(delta, 0.0));
+  }
+
+  testWidgets('Can change value using CupertinoSlider', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.MyApp(),
+    );
+
+    // Check for the initial slider value.
+    expect(find.text('0.0'), findsOneWidget);
+
+    await _dragSlider(tester, const Key('slider'));
+    await tester.pumpAndSettle();
+
+    // Check for the updated slider value.
+    expect(find.text('40.0'), findsOneWidget);
+  });
+}

packages/flutter/lib/src/cupertino/slider.dart

@@ -35,6 +35,12 @@ import 'thumb_painter.dart';
 /// that use a slider will listen for the [onChanged] callback and rebuild the
 /// slider with a new [value] to update the visual appearance of the slider.
 ///
+/// {@tool dartpad}
+/// This example shows how to show the current slider value as it changes.
+///
+/// ** See code in examples/api/lib/cupertino/slider/cupertino_slider.0.dart **
+/// {@end-tool}
+///
 /// See also:
 ///
 ///  * <https://developer.apple.com/ios/human-interface-guidelines/controls/sliders/>