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82 lines
2.4 KiB
Dart
82 lines
2.4 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 'package:sky/animation/scroll_behavior.dart';
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import 'package:sky/widgets/basic.dart';
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import 'package:sky/widgets/block_viewport.dart';
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import 'package:sky/widgets/scrollable.dart';
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import 'package:sky/widgets/widget.dart';
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class VariableHeightScrollable extends Scrollable {
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VariableHeightScrollable({
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String key,
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this.builder,
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this.token,
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this.layoutState
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}) : super(key: key);
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IndexedBuilder builder;
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Object token;
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BlockViewportLayoutState layoutState;
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// When the token changes the scrollable's contents may have
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// changed. Remember as much so that after the new contents
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// have been laid out we can adjust the scrollOffset so that
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// the last page of content is still visible.
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bool _contentsChanged = true;
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void initState() {
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assert(layoutState != null);
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layoutState.removeListener(_handleLayoutChanged);
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layoutState.addListener(_handleLayoutChanged);
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super.initState();
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}
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void syncFields(VariableHeightScrollable source) {
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builder = source.builder;
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if (token != source.token)
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_contentsChanged = true;
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token = source.token;
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if (layoutState != source.layoutState) {
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// Warning: this is unlikely to be what you intended.
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assert(source.layoutState != null);
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layoutState == source.layoutState;
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layoutState.removeListener(_handleLayoutChanged);
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layoutState.addListener(_handleLayoutChanged);
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}
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super.syncFields(source);
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}
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ScrollBehavior createScrollBehavior() => new OverscrollBehavior();
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OverscrollBehavior get scrollBehavior => super.scrollBehavior;
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void _handleSizeChanged(Size newSize) {
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scrollBehavior.containerSize = newSize.height;
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}
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void _handleLayoutChanged() {
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if (layoutState.didReachLastChild) {
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scrollBehavior.contentsSize = layoutState.contentsSize;
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if (_contentsChanged && scrollOffset > scrollBehavior.maxScrollOffset) {
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_contentsChanged = false;
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settleScrollOffset();
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}
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} else {
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scrollBehavior.contentsSize = double.INFINITY;
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}
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}
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Widget buildContent() {
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return new SizeObserver(
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callback: _handleSizeChanged,
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child: new BlockViewport(
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builder: builder,
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layoutState: layoutState,
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startOffset: scrollOffset,
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token: token
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)
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);
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}
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}
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