sliver_list_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_test/flutter_test.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter/material.dart';

void main() {
  testWidgets('SliverList reverse children (with keys)', (WidgetTester tester) async {
    final List<int> items = List<int>.generate(20, (int i) => i);
    const double itemHeight = 300.0;
    const double viewportHeight = 500.0;

    const double scrollPosition = 18 * itemHeight;
    final ScrollController controller = ScrollController(initialScrollOffset: scrollPosition);

    await tester.pumpWidget(_buildSliverList(
      items: items,
      controller: controller,
      itemHeight: itemHeight,
      viewportHeight: viewportHeight,
    ));
    await tester.pumpAndSettle();

    expect(controller.offset, scrollPosition);
    expect(find.text('Tile 0'), findsNothing);
    expect(find.text('Tile 1'), findsNothing);
    expect(find.text('Tile 18'), findsOneWidget);
    expect(find.text('Tile 19'), findsOneWidget);

    await tester.pumpWidget(_buildSliverList(
      items: items.reversed.toList(),
      controller: controller,
      itemHeight: itemHeight,
      viewportHeight: viewportHeight,
    ));
    final int frames = await tester.pumpAndSettle();
    expect(frames, 1); // ensures that there is no (animated) bouncing of the scrollable

    expect(controller.offset, scrollPosition);
    expect(find.text('Tile 19'), findsNothing);
    expect(find.text('Tile 18'), findsNothing);
    expect(find.text('Tile 1'), findsOneWidget);
    expect(find.text('Tile 0'), findsOneWidget);

    controller.jumpTo(0.0);
    await tester.pumpAndSettle();

    expect(controller.offset, 0.0);
    expect(find.text('Tile 19'), findsOneWidget);
    expect(find.text('Tile 18'), findsOneWidget);
    expect(find.text('Tile 1'), findsNothing);
    expect(find.text('Tile 0'), findsNothing);
  });

  testWidgets('SliverList replace children (with keys)', (WidgetTester tester) async {
    final List<int> items = List<int>.generate(20, (int i) => i);
    const double itemHeight = 300.0;
    const double viewportHeight = 500.0;

    const double scrollPosition = 18 * itemHeight;
    final ScrollController controller = ScrollController(initialScrollOffset: scrollPosition);

    await tester.pumpWidget(_buildSliverList(
      items: items,
      controller: controller,
      itemHeight: itemHeight,
      viewportHeight: viewportHeight,
    ));
    await tester.pumpAndSettle();

    expect(controller.offset, scrollPosition);
    expect(find.text('Tile 0'), findsNothing);
    expect(find.text('Tile 1'), findsNothing);
    expect(find.text('Tile 18'), findsOneWidget);
    expect(find.text('Tile 19'), findsOneWidget);

    await tester.pumpWidget(_buildSliverList(
      items: items.map<int>((int i) => i + 100).toList(),
      controller: controller,
      itemHeight: itemHeight,
      viewportHeight: viewportHeight,
    ));
    final int frames = await tester.pumpAndSettle();
    expect(frames, 1); // ensures that there is no (animated) bouncing of the scrollable

    expect(controller.offset, scrollPosition);
    expect(find.text('Tile 0'), findsNothing);
    expect(find.text('Tile 1'), findsNothing);
    expect(find.text('Tile 18'), findsNothing);
    expect(find.text('Tile 19'), findsNothing);

    expect(find.text('Tile 100'), findsNothing);
    expect(find.text('Tile 101'), findsNothing);
    expect(find.text('Tile 118'), findsOneWidget);
    expect(find.text('Tile 119'), findsOneWidget);

    controller.jumpTo(0.0);
    await tester.pumpAndSettle();

    expect(controller.offset, 0.0);
    expect(find.text('Tile 100'), findsOneWidget);
    expect(find.text('Tile 101'), findsOneWidget);
    expect(find.text('Tile 118'), findsNothing);
    expect(find.text('Tile 119'), findsNothing);
  });

  testWidgets('SliverList replace with shorter children list (with keys)', (WidgetTester tester) async {
    final List<int> items = List<int>.generate(20, (int i) => i);
    const double itemHeight = 300.0;
    const double viewportHeight = 500.0;

    final double scrollPosition = items.length * itemHeight - viewportHeight;
    final ScrollController controller = ScrollController(initialScrollOffset: scrollPosition);

    await tester.pumpWidget(_buildSliverList(
      items: items,
      controller: controller,
      itemHeight: itemHeight,
      viewportHeight: viewportHeight,
    ));
    await tester.pumpAndSettle();

    expect(controller.offset, scrollPosition);
    expect(find.text('Tile 0'), findsNothing);
    expect(find.text('Tile 1'), findsNothing);
    expect(find.text('Tile 17'), findsNothing);
    expect(find.text('Tile 18'), findsOneWidget);
    expect(find.text('Tile 19'), findsOneWidget);

    await tester.pumpWidget(_buildSliverList(
      items: items.sublist(0, items.length - 1),
      controller: controller,
      itemHeight: itemHeight,
      viewportHeight: viewportHeight,
    ));
    final int frames = await tester.pumpAndSettle();
    expect(frames, greaterThan(1)); // ensure animation to bring tile17 into view

    expect(controller.offset, scrollPosition - itemHeight);
    expect(find.text('Tile 0'), findsNothing);
    expect(find.text('Tile 1'), findsNothing);
    expect(find.text('Tile 17'), findsOneWidget);
    expect(find.text('Tile 18'), findsOneWidget);
    expect(find.text('Tile 19'), findsNothing);
  });

  testWidgets('SliverList should layout first child in case of child reordering', (WidgetTester tester) async {
    // Regression test for https://github.com/flutter/flutter/issues/35904.
    List<String> items = <String>['1', '2'];

    await tester.pumpWidget(_buildSliverListRenderWidgetChild(items));
    await tester.pumpAndSettle();

    expect(find.text('Tile 1'), findsOneWidget);
    expect(find.text('Tile 2'), findsOneWidget);

    items = items.reversed.toList();
    await tester.pumpWidget(_buildSliverListRenderWidgetChild(items));
    await tester.pumpAndSettle();

    expect(find.text('Tile 1'), findsOneWidget);
    expect(find.text('Tile 2'), findsOneWidget);
  });
}

Widget _buildSliverListRenderWidgetChild(List<String> items) {
  return MaterialApp(
    home: Directionality(
      textDirection: TextDirection.ltr,
      child: Material(
        child: Container(
          height: 500,
          child: CustomScrollView(
            controller: ScrollController(),
            slivers: <Widget>[
              SliverList(
                delegate: SliverChildListDelegate(
                  items.map<Widget>((String item) {
                    return Chip(
                      key: Key(item),
                      label: Text('Tile $item'),
                    );
                  }).toList(),
                ),
              ),
            ],
          ),
        ),
      ),
    ),
  );
}

Widget _buildSliverList({
  List<int> items = const <int>[],
  ScrollController controller,
  double itemHeight = 500.0,
  double viewportHeight = 300.0,
}) {
  return Directionality(
    textDirection: TextDirection.ltr,
    child: Center(
      child: Container(
        height: viewportHeight,
        child: CustomScrollView(
          controller: controller,
          slivers: <Widget>[
            SliverList(
              delegate: SliverChildBuilderDelegate(
                (BuildContext context, int i) {
                  return Container(
                    key: ValueKey<int>(items[i]),
                    height: itemHeight,
                    child: Text('Tile ${items[i]}'),
                  );
                },
                childCount: items.length,
              ),
            ),
          ],
        ),
      ),
    ),
  );
}