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When using OverscrollCurve, we continue to scroll beyond the top of the scrollable area but the scroll delta is reduced by 2x. A future CL will add an animation at gesturescrollend to relax back to scroll position 0.0. R=eseidel@chromium.org Review URL: https://codereview.chromium.org/1002953003
88 lines
2.5 KiB
Dart
88 lines
2.5 KiB
Dart
// Copyright 2015 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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import '../animation/scroll_curve.dart';
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import '../fn.dart';
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import 'dart:math' as math;
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import 'dart:sky' as sky;
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import 'scrollable.dart';
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abstract class FixedHeightScrollable extends Scrollable {
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// TODO(rafaelw): This component really shouldn't have an opinion
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// about how it is sized. The owning component should decide whether
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// it's explicitly sized or flexible or whatever...
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static final Style _style = new Style('''
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overflow: hidden;
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position: relative;
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flex: 1;
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will-change: transform;'''
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);
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static final Style _scrollAreaStyle = new Style('''
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position:relative;
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will-change: transform;'''
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);
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double _height = 0.0;
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double _itemHeight;
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FixedHeightScrollable({
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Object key,
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ScrollCurve scrollCurve
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}) : super(key: key, scrollCurve: scrollCurve);
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void didMount() {
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super.didMount();
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var root = getRoot();
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var item = root.firstChild.firstChild;
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sky.ClientRect scrollRect = root.getBoundingClientRect();
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sky.ClientRect itemRect = item.getBoundingClientRect();
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assert(scrollRect.height > 0);
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assert(itemRect.height > 0);
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setState(() {
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_height = scrollRect.height;
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_itemHeight = itemRect.height;
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});
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}
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Node build() {
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var itemNumber = 0;
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var drawCount = 1;
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var transformStyle = '';
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if (_height > 0.0) {
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if (scrollOffset < 0.0) {
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double visibleHeight = _height + scrollOffset;
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drawCount = (visibleHeight / _itemHeight).round() + 1;
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transformStyle =
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'transform: translateY(${(-scrollOffset).toStringAsFixed(2)}px)';
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} else {
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drawCount = (_height / _itemHeight).round() + 1;
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double alignmentOffset = math.max(0.0, scrollOffset);
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double alignmentDelta = -scrollOffset % _itemHeight;
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if (alignmentDelta != 0.0)
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alignmentDelta -= _itemHeight;
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double drawStart = scrollOffset + alignmentDelta;
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itemNumber = (drawStart / _itemHeight).floor();
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transformStyle =
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'transform: translateY(${(alignmentDelta).toStringAsFixed(2)}px)';
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}
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}
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return new Container(
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styles: [_style],
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children: [
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new Container(
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styles: [_scrollAreaStyle],
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inlineStyle: transformStyle,
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children: buildItems(itemNumber, drawCount)
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)
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]
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);
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}
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}
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