Leaf Petersen
745f112ef6
Opt an initial batch of files under samples, samples-dev, utils, and runtime/tools/dartfuzz out of null safety in preparation for switching the flag on by default. Change-Id: Icdfd52a5a969e678a7205903332f73fe3841c223 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/166960 Reviewed-by: Daco Harkes <dacoharkes@google.com> Commit-Queue: Leaf Petersen <leafp@google.com>
69 lines
1.9 KiB
Dart
69 lines
1.9 KiB
Dart
// Copyright (c) 2011, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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// @dart = 2.9
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part of touch;
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abstract class ScrollListener {
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/**
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* The callback invoked for a scroll event.
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* [decelerating] specifies whether or not the content is moving due
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* to deceleration. It should be false if the content is moving because the
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* user is dragging the content.
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*/
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void onScrollerMoved(double scrollX, double scrollY, bool decelerating);
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}
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/**
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* The scroll watcher is intended to provide a single way to
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* listen for scroll events from instances of Scroller.
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* TODO(jacobr): this class is obsolete.
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*/
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class ScrollWatcher {
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Scroller _scroller;
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List<ScrollListener> _listeners;
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Element _scrollerEl;
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ScrollWatcher(Scroller scroller)
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: _scroller = scroller,
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_listeners = new List<ScrollListener>() {}
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void addListener(ScrollListener listener) {
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_listeners.add(listener);
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}
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/**
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* Send the scroll event to all listeners.
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* [decelerating] is true if the offset is changing because of deceleration.
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*/
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void _dispatchScroll(num scrollX, num scrollY, [bool decelerating = false]) {
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for (final listener in _listeners) {
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listener.onScrollerMoved(scrollX, scrollY, decelerating);
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}
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}
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/**
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* Initializes elements and event handlers. Must be called after construction
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* and before usage.
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*/
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void initialize() {
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_scrollerEl = _scroller.getElement();
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_scroller.onContentMoved.listen((e) {
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_onContentMoved(e);
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});
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}
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/**
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* This callback is invoked any time the scroller content offset changes.
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*/
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void _onContentMoved(Event e) {
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num scrollX = _scroller.getHorizontalOffset();
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num scrollY = _scroller.getVerticalOffset();
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_dispatchScroll(scrollX, scrollY);
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}
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}
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