RefreshIndicator: Add notificationPredicate example (#103894)

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

@@ -11,21 +11,16 @@ void main() => runApp(const MyApp());
 class MyApp extends StatelessWidget {
   const MyApp({super.key});
 
-  static const String _title = 'RefreshIndicator Sample';
-
   @override
   Widget build(BuildContext context) {
     return const MaterialApp(
-      title: _title,
-      home: RefreshIndicatorExample(title: _title),
+      home: RefreshIndicatorExample(),
     );
   }
 }
 
 class RefreshIndicatorExample extends StatefulWidget {
-  const RefreshIndicatorExample({super.key, required this.title});
-
-  final String title;
+  const RefreshIndicatorExample({super.key});
 
   @override
   State<RefreshIndicatorExample> createState() => _RefreshIndicatorExampleState();
@@ -39,7 +34,7 @@ class _RefreshIndicatorExampleState extends State<RefreshIndicatorExample> {
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
-        title: Text(widget.title),
+        title: const Text('RefreshIndicator Sample'),
       ),
       body: RefreshIndicator(
         key: _refreshIndicatorKey,

examples/api/lib/material/refresh_indicator/refresh_indicator.1.dart

@@ -0,0 +1,87 @@
+// 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 RefreshIndicator
+
+import 'package:flutter/material.dart';
+
+void main() => runApp(const MyApp());
+
+class MyApp extends StatelessWidget {
+  const MyApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return const MaterialApp(
+      home: RefreshIndicatorExample(),
+    );
+  }
+}
+
+class RefreshIndicatorExample extends StatelessWidget {
+  const RefreshIndicatorExample({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('RefreshIndicator Sample'),
+      ),
+      body: RefreshIndicator(
+        color: Colors.white,
+        backgroundColor: Colors.blue,
+        onRefresh: () async {
+          // Replace this delay with the code to be executed during refresh
+          // and return asynchronous code
+          return Future<void>.delayed(const Duration(seconds: 3));
+        },
+        // This check is used to customize listening to scroll notifications
+        // from the widget's children.
+        //
+        // By default this is set to `notification.depth == 0`, which ensures
+        // the only the scroll notifications from the first child are listened to.
+        //
+        // Here setting `notification.depth == 1` triggers the refresh indicator
+        // when overscrolling the nested scroll view.
+        notificationPredicate: (ScrollNotification notification) {
+          return notification.depth == 1;
+        },
+        child: SingleChildScrollView(
+          child: Column(
+            children: <Widget>[
+              Container(
+                height: 100,
+                alignment: Alignment.center,
+                color: Colors.pink[100],
+                child: Column(
+                  mainAxisAlignment: MainAxisAlignment.center,
+                  children: <Widget>[
+                    Text(
+                      'Pull down here',
+                      style: Theme.of(context).textTheme.headlineMedium,
+                    ),
+                    const Text("RefreshIndicator won't trigger"),
+                  ],
+                ),
+              ),
+              Container(
+                color: Colors.green[100],
+                child: ListView.builder(
+                  shrinkWrap: true,
+                  itemCount: 25,
+                  itemBuilder: (BuildContext context, int index) {
+                    return const ListTile(
+                      title: Text('Pull down here'),
+                      subtitle: Text('RefreshIndicator will trigger'),
+                    );
+                  },
+                ),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}

examples/api/test/material/refresh_indicator/refresh_indicator.1_test.dart

@@ -0,0 +1,27 @@
+// 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/refresh_indicator/refresh_indicator.1.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Pulling from nested scroll view triggers refresh indicator', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.MyApp(),
+    );
+
+    // Pull from the upper scroll view.
+    await tester.fling(find.text('Pull down here').first, const Offset(0.0, 300.0), 1000.0);
+    await tester.pump();
+    expect(find.byType(RefreshProgressIndicator), findsNothing);
+    await tester.pumpAndSettle(); // Advance pending time
+
+    // Pull from the nested scroll view.
+    await tester.fling(find.text('Pull down here').at(3), const Offset(0.0, 300.0), 1000.0);
+    await tester.pump();
+    expect(find.byType(RefreshProgressIndicator), findsOneWidget);
+    await tester.pumpAndSettle(); // Advance pending time
+  });
+}

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

@@ -78,6 +78,13 @@ enum RefreshIndicatorTriggerMode {
 /// ** See code in examples/api/lib/material/refresh_indicator/refresh_indicator.0.dart **
 /// {@end-tool}
 ///
+/// {@tool dartpad}
+/// This example shows how to trigger [RefreshIndicator] in a nested scroll view using
+/// the [notificationPredicate] property.
+///
+/// ** See code in examples/api/lib/material/refresh_indicator/refresh_indicator.1.dart **
+/// {@end-tool}
+///
 /// ## Troubleshooting
 ///
 /// ### Refresh indicator does not show up