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0fcbeef342
This CL makes FixedHeightScrollable able to measure heights. In the DOM-based version, FixedHeightScrollable forced a synchronous layout in a microtask in order to measure the size of itself and its children. In the DOM-less version, we now require the subclass to tell us the item height and we measure our own height using a layout callback. R=ianh@google.com Review URL: https://codereview.chromium.org/1161063005
78 lines
2.2 KiB
Dart
78 lines
2.2 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_behavior.dart';
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import '../fn2.dart';
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import 'dart:async';
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import 'dart:math' as math;
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import 'dart:sky' as sky;
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import 'package:vector_math/vector_math.dart';
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import 'scrollable.dart';
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abstract class FixedHeightScrollable extends Scrollable {
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FixedHeightScrollable({ this.itemHeight, Object key }) : super(key: key) {
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assert(itemHeight != null);
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}
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ScrollBehavior createScrollBehavior() => new OverscrollBehavior();
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OverscrollBehavior get scrollBehavior => super.scrollBehavior as OverscrollBehavior;
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double _height;
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final double itemHeight;
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int _itemCount = 0;
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int get itemCount => _itemCount;
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void set itemCount (int value) {
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if (_itemCount != value) {
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_itemCount = value;
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scrollBehavior.contentsHeight = itemHeight * _itemCount;
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}
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}
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void _handleSizeChanged(sky.Size newSize) {
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setState(() {
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_height = newSize.height;
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scrollBehavior.containerHeight = _height;
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});
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}
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UINode buildContent() {
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var itemNumber = 0;
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var itemCount = 0;
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Matrix4 transform = new Matrix4.identity();
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if (_height != null && _height > 0.0) {
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if (scrollOffset < 0.0) {
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double visibleHeight = _height + scrollOffset;
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itemCount = (visibleHeight / itemHeight).round() + 1;
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transform.translate(0.0, -scrollOffset);
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} else {
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itemCount = (_height / itemHeight).ceil() + 1;
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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 = math.max(0, (drawStart / itemHeight).floor());
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transform.translate(0.0, alignmentDelta);
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}
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}
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return new SizeObserver(
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callback: _handleSizeChanged,
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child: new Clip(
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child: new Transform(
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transform: transform,
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child: new BlockContainer(
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children: buildItems(itemNumber, itemCount))
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)
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)
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);
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}
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List<UINode> buildItems(int start, int count);
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}
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