packages/flutter/test/widgets/scrollable_of_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/widgets.dart';
import 'package:flutter_test/flutter_test.dart';

class ScrollPositionListener extends StatefulWidget {
  const ScrollPositionListener({ Key? key, required this.child, required this.log}) : super(key: key);

  final Widget child;
  final ValueChanged<String> log;

  @override
  State<ScrollPositionListener> createState() => _ScrollPositionListenerState();
}

class _ScrollPositionListenerState extends State<ScrollPositionListener> {
  ScrollPosition? _position;

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    _position?.removeListener(listener);
    _position = Scrollable.of(context)?.position;
    _position?.addListener(listener);
    widget.log('didChangeDependencies ${_position?.pixels.toStringAsFixed(1)}');
  }

  @override
  void dispose() {
    _position?.removeListener(listener);
    super.dispose();
  }

  @override
  Widget build(BuildContext context) => widget.child;

  void listener() {
    widget.log('listener ${_position?.pixels.toStringAsFixed(1)}');
  }

}

void main() {
  testWidgets('Scrollable.of() dependent rebuilds when Scrollable position changes', (WidgetTester tester) async {
    late String logValue;
    final ScrollController controller = ScrollController();

    // Changing the SingleChildScrollView's physics causes the
    // ScrollController's ScrollPosition to be rebuilt.

    Widget buildFrame(ScrollPhysics? physics) {
      return SingleChildScrollView(
        controller: controller,
        physics: physics,
        child: ScrollPositionListener(
          log: (String s) { logValue = s; },
          child: const SizedBox(height: 400.0),
        ),
      );
    }

    await tester.pumpWidget(buildFrame(null));
    expect(logValue, 'didChangeDependencies 0.0');

    controller.jumpTo(100.0);
    expect(logValue, 'listener 100.0');

    await tester.pumpWidget(buildFrame(const ClampingScrollPhysics()));
    expect(logValue, 'didChangeDependencies 100.0');

    controller.jumpTo(200.0);
    expect(logValue, 'listener 200.0');

    controller.jumpTo(300.0);
    expect(logValue, 'listener 300.0');

    await tester.pumpWidget(buildFrame(const BouncingScrollPhysics()));
    expect(logValue, 'didChangeDependencies 300.0');

    controller.jumpTo(400.0);
    expect(logValue, 'listener 400.0');
  });

  testWidgets('Scrollable.of() is possible using ScrollNotification context', (WidgetTester tester) async {
    late ScrollNotification notification;

    await tester.pumpWidget(NotificationListener<ScrollNotification>(
      onNotification: (ScrollNotification value) {
        notification = value;
        return false;
      },
      child: const SingleChildScrollView(
        child: SizedBox(height: 1200.0),
      ),
    ));

    await tester.startGesture(const Offset(100.0, 100.0));
    await tester.pump(const Duration(seconds: 1));

    final StatefulElement scrollableElement = find.byType(Scrollable).evaluate().first as StatefulElement;
    expect(Scrollable.of(notification.context!), equals(scrollableElement.state));
  });
}