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74575775bd
This fixes some theoretical bugs whereby we were using hashCode to try
to get unique keys for objects, but really we wanted object identity.
It also lays the groundwork for a new GlobalKey concept.
I tried to keep the impact on the code minimal, which is why the "Key"
constructor is actually a factory that returns a StringKey. The code
has this class hierarchy:
```
KeyBase
|
Key--------------+---------------+
| | |
StringKey ObjectKey UniqueKey
```
...where the constructors are Key and Key.stringify (StringKey),
Key.fromObjectIdentity (ObjectKey), and Key.unique (UniqueKey).
We could instead of factory methods use regular constructors with the
following hierarchy:
```
KeyBase
|
LocalKey---------+---------------+
| | |
Key ObjectIdentityKey UniqueKey
```
...with constructors Key, Key.stringify, ObjectIdentityKey, and
UniqueKey, but I felt that that was maybe a more confusing hierarchy.
I don't have a strong opinion on this.
92 lines
2.6 KiB
Dart
92 lines
2.6 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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export 'package:sky/widgets/block_viewport.dart' show BlockViewportLayoutState;
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class VariableHeightScrollable extends Scrollable {
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VariableHeightScrollable({
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Key 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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super.initState();
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}
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void didMount() {
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layoutState.addListener(_handleLayoutChanged);
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super.didMount();
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}
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void didUnmount() {
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layoutState.removeListener(_handleLayoutChanged);
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super.didUnmount();
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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.removeListener(_handleLayoutChanged);
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layoutState = source.layoutState;
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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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