sliver_fixed_extent_layout_test.dart 3.01 KB
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// Copyright 2014 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/rendering.dart';
import '../flutter_test_alternative.dart';

import 'rendering_tester.dart';

void main() {
  test('RenderSliverFixedExtentList layout test - rounding error', () {
    final List<RenderBox> children = <RenderBox>[
      RenderSizedBox(const Size(400.0, 100.0)),
      RenderSizedBox(const Size(400.0, 100.0)),
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      RenderSizedBox(const Size(400.0, 100.0)),
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    ];
    final TestRenderSliverBoxChildManager childManager = TestRenderSliverBoxChildManager(
      children: children,
    );
    final RenderViewport root = RenderViewport(
      axisDirection: AxisDirection.down,
      crossAxisDirection: AxisDirection.right,
      offset: ViewportOffset.zero(),
      cacheExtent: 0,
      children: <RenderSliver>[
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        childManager.createRenderSliverFillViewport(),
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      ],
    );
    layout(root);
    expect(children[0].attached, true);
    expect(children[1].attached, false);

    root.offset = ViewportOffset.fixed(600);
    pumpFrame();
    expect(children[0].attached, false);
    expect(children[1].attached, true);

    // Simulate double precision error.
    root.offset = ViewportOffset.fixed(1199.999999999998);
    pumpFrame();
    expect(children[1].attached, false);
    expect(children[2].attached, true);
  });
}

class TestRenderSliverBoxChildManager extends RenderSliverBoxChildManager {
  TestRenderSliverBoxChildManager({
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    required this.children,
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  });

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  RenderSliverMultiBoxAdaptor? _renderObject;
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  List<RenderBox> children;

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  RenderSliverFillViewport createRenderSliverFillViewport() {
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    assert(_renderObject == null);
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    _renderObject = RenderSliverFillViewport(
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      childManager: this,
    );
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    return _renderObject as RenderSliverFillViewport;
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  }

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  int? _currentlyUpdatingChildIndex;
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  @override
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  void createChild(int index, { required RenderBox? after }) {
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    if (index < 0 || index >= children.length)
      return;
    try {
      _currentlyUpdatingChildIndex = index;
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      _renderObject!.insert(children[index], after: after);
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    } finally {
      _currentlyUpdatingChildIndex = null;
    }
  }

  @override
  void removeChild(RenderBox child) {
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    _renderObject!.remove(child);
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  }

  @override
  double estimateMaxScrollOffset(
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    SliverConstraints constraints, {
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    int? firstIndex,
    int? lastIndex,
    double? leadingScrollOffset,
    double? trailingScrollOffset,
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  }) {
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    assert(lastIndex! >= firstIndex!);
    return children.length * (trailingScrollOffset! - leadingScrollOffset!) / (lastIndex! - firstIndex! + 1);
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  }

  @override
  int get childCount => children.length;

  @override
  void didAdoptChild(RenderBox child) {
    assert(_currentlyUpdatingChildIndex != null);
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    final SliverMultiBoxAdaptorParentData childParentData = child.parentData as SliverMultiBoxAdaptorParentData;
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    childParentData.index = _currentlyUpdatingChildIndex;
  }

  @override
  void setDidUnderflow(bool value) { }
}