// Copyright 2016 The Chromium Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. import 'dart:ui' show VoidCallback; import 'package:flutter/foundation.dart'; /// The status of an animation enum AnimationStatus { /// The animation is stopped at the beginning dismissed, /// The animation is running from beginning to end forward, /// The animation is running backwards, from end to beginning reverse, /// The animation is stopped at the end completed, } /// Signature for listeners attached using [Animation.addStatusListener]. typedef void AnimationStatusListener(AnimationStatus status); /// An animation with a value of type `T`. /// /// An animation consists of a value (of type `T`) together with a status. The /// status indicates whether the animation is conceptually running from /// beginning to end or from the end back to the beginning, although the actual /// value of the animation might not change monotonically (e.g., if the /// animation uses a curve that bounces). /// /// Animations also let other objects listen for changes to either their value /// or their status. These callbacks are called during the "animation" phase of /// the pipeline, just prior to rebuilding widgets. /// /// To create a new animation that you can run forward and backward, consider /// using [AnimationController]. abstract class Animation<T> extends Listenable implements ValueListenable<T> { /// Abstract const constructor. This constructor enables subclasses to provide /// const constructors so that they can be used in const expressions. const Animation(); // keep these next five dartdocs in sync with the dartdocs in AnimationWithParentMixin<T> /// Calls the listener every time the value of the animation changes. /// /// Listeners can be removed with [removeListener]. @override void addListener(VoidCallback listener); /// Stop calling the listener every time the value of the animation changes. /// /// Listeners can be added with [addListener]. @override void removeListener(VoidCallback listener); /// Calls listener every time the status of the animation changes. /// /// Listeners can be removed with [removeStatusListener]. void addStatusListener(AnimationStatusListener listener); /// Stops calling the listener every time the status of the animation changes. /// /// Listeners can be added with [addStatusListener]. void removeStatusListener(AnimationStatusListener listener); /// The current status of this animation. AnimationStatus get status; /// The current value of the animation. @override T get value; /// Whether this animation is stopped at the beginning. bool get isDismissed => status == AnimationStatus.dismissed; /// Whether this animation is stopped at the end. bool get isCompleted => status == AnimationStatus.completed; @override String toString() { return '${describeIdentity(this)}(${toStringDetails()})'; } /// Provides a string describing the status of this object, but not including /// information about the object itself. /// /// This function is used by [Animation.toString] so that [Animation] /// subclasses can provide additional details while ensuring all [Animation] /// subclasses have a consistent [toString] style. /// /// The result of this function includes an icon describing the status of this /// [Animation] object: /// /// * "▶": [AnimationStatus.forward] ([value] increasing) /// * "◀": [AnimationStatus.reverse] ([value] decreasing) /// * "⏭": [AnimationStatus.completed] ([value] == 1.0) /// * "⏮": [AnimationStatus.dismissed] ([value] == 0.0) String toStringDetails() { assert(status != null); String icon; switch (status) { case AnimationStatus.forward: icon = '\u25B6'; // > break; case AnimationStatus.reverse: icon = '\u25C0'; // < break; case AnimationStatus.completed: icon = '\u23ED'; // >>| break; case AnimationStatus.dismissed: icon = '\u23EE'; // |<< break; } assert(icon != null); return '$icon'; } }