custom_scroll_view.dart

// Copyright 2013 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 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter/scheduler.dart';
import 'package:flutter_test/flutter_test.dart';

import 'diagram_step.dart';
import 'fake_drag_scroll_activity.dart';
import 'utils.dart';

final Duration _kTotalDuration = _kScrollUpDuration +
    _kScrollPauseDuration +
    _kScrollDownDurationPartOne +
    _kScrollPauseDuration +
    _kScrollDownDurationPartTwo +
    _kScrollPauseDuration;
const Duration _kScrollUpDuration = Duration(seconds: 1, milliseconds: 500);
const Duration _kScrollDownDurationPartOne = Duration(milliseconds: 800);
const Duration _kScrollDownDurationPartTwo = Duration(seconds: 1);
const Duration _kScrollPauseDuration = Duration(milliseconds: 900);

const String _customScrollView = 'custom_scroll_view';

class CustomScrollViewDiagram extends StatefulWidget with DiagramMetadata {
  const CustomScrollViewDiagram(this.name, {super.key});

  @override
  final String name;

  @override
  State<StatefulWidget> createState() => _CustomScrollViewDiagramState();

  @override
  Duration? get duration => _kTotalDuration;
}

class _CustomScrollViewDiagramState extends State<CustomScrollViewDiagram>
    with TickerProviderStateMixin, LockstepStateMixin {
  final ScrollController _scrollController = ScrollController();

  @override
  void initState() {
    super.initState();
    SchedulerBinding.instance.scheduleFrameCallback((Duration _) {
      _play();
    });
  }

  @override
  void didUpdateWidget(CustomScrollViewDiagram oldWidget) {
    super.didUpdateWidget(oldWidget);
    _scrollController.jumpTo(0.0);
    SchedulerBinding.instance.scheduleFrameCallback((Duration _) {
      _play();
    });
  }

  Future<void> _play() async {
    await waitLockstep(_kScrollPauseDuration);
    await _animate(
      to: 650.0,
      duration: _kScrollUpDuration,
    );
    await waitLockstep(_kScrollPauseDuration);
    await _animate(
      to: 500.0,
      duration: _kScrollDownDurationPartOne,
    );
    await waitLockstep(_kScrollPauseDuration);
    await _animate(
      to: 0.0,
      duration: _kScrollDownDurationPartTwo,
    );
  }

  Future<void> _animate({required double to, required Duration duration}) {
    final ScrollPositionWithSingleContext position =
        _scrollController.position as ScrollPositionWithSingleContext;
    final FakeDragScrollActivity activity = FakeDragScrollActivity(
      position,
      from: _scrollController.offset,
      to: to,
      duration: duration,
      curve: Curves.easeInOut,
      vsync: this,
    );
    _scrollController.position.beginActivity(activity);
    return activity.done;
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.white,
      height: 400.0,
      width: 376.0,
      child: CustomScrollView(
        controller: _scrollController,
        slivers: <Widget>[
          const SliverAppBar(
            pinned: true,
            expandedHeight: 250.0,
            flexibleSpace: FlexibleSpaceBar(
              title: Text('Demo'),
            ),
          ),
          SliverGrid(
            gridDelegate: const SliverGridDelegateWithMaxCrossAxisExtent(
              maxCrossAxisExtent: 200.0,
              mainAxisSpacing: 10.0,
              crossAxisSpacing: 10.0,
              childAspectRatio: 4.0,
            ),
            delegate: SliverChildBuilderDelegate(
              (BuildContext context, int index) {
                return Container(
                  alignment: Alignment.center,
                  color: Colors.teal[100 * (index % 9)],
                  child: Text('Grid Item $index'),
                );
              },
              childCount: 20,
            ),
          ),
          SliverFixedExtentList(
            itemExtent: 50.0,
            delegate: SliverChildBuilderDelegate(
              (BuildContext context, int index) {
                return Container(
                  alignment: Alignment.center,
                  color: Colors.lightBlue[100 * (index % 9)],
                  child: Text('List Item $index'),
                );
              },
            ),
          ),
        ],
      ),
    );
  }
}

class CustomScrollViewDiagramStep extends DiagramStep {
  @override
  final String category = 'widgets';

  @override
  Future<List<CustomScrollViewDiagram>> get diagrams async =>
      <CustomScrollViewDiagram>[
        const CustomScrollViewDiagram(_customScrollView),
      ];
}