1/*
2 * Copyright (C) 2017 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package androidx.transition;
18
19import android.view.ViewGroup;
20
21/**
22 * Extend <code>TransitionPropagation</code> to customize start delays for Animators created
23 * in {@link Transition#createAnimator(ViewGroup, TransitionValues, TransitionValues)}.
24 * A Transition such as {@link Explode} defaults to using {@link CircularPropagation} and Views
25 * closer to the epicenter will move out of the scene later and into the scene sooner than Views
26 * farther from the epicenter, giving the appearance of inertia. With no TransitionPropagation, all
27 * Views will react simultaneously to the start of the transition.
28 *
29 * @see Transition#setPropagation(TransitionPropagation)
30 * @see Transition#getEpicenter()
31 */
32public abstract class TransitionPropagation {
33
34    /**
35     * Called by Transition to alter the Animator start delay. All start delays will be adjusted
36     * such that the minimum becomes zero.
37     *
38     * @param sceneRoot   The root of the View hierarchy running the transition.
39     * @param transition  The transition that created the Animator
40     * @param startValues The values for a specific target in the start scene.
41     * @param endValues   The values for the target in the end scene.
42     * @return A start delay to use with the Animator created by <code>transition</code>. The
43     * delay will be offset by the minimum delay of all <code>TransitionPropagation</code>s
44     * used in the Transition so that the smallest delay will be 0. Returned values may be
45     * negative.
46     */
47    public abstract long getStartDelay(ViewGroup sceneRoot, Transition transition,
48            TransitionValues startValues, TransitionValues endValues);
49
50    /**
51     * Captures the values in the start or end scene for the properties that this
52     * transition propagation monitors. These values are then passed as the startValues
53     * or endValues structure in a later call to
54     * {@link #getStartDelay(ViewGroup, Transition, TransitionValues, TransitionValues)}.
55     * The main concern for an implementation is what the
56     * properties are that the transition cares about and what the values are
57     * for all of those properties. The start and end values will be compared
58     * later during the
59     * {@link #getStartDelay(ViewGroup, Transition, TransitionValues, TransitionValues)}.
60     * method to determine the start delay.
61     *
62     * <p>Subclasses must implement this method. The method should only be called by the
63     * transition system; it is not intended to be called from external classes.</p>
64     *
65     * @param transitionValues The holder for any values that the Transition
66     *                         wishes to store. Values are stored in the <code>values</code> field
67     *                         of this TransitionValues object and are keyed from
68     *                         a String value. For example, to store a view's rotation value,
69     *                         a transition might call
70     *                         <code>transitionValues.values.put("appname:transitionname:rotation",
71     *                         view.getRotation())</code>. The target view will already be stored
72     *                         in
73     *                         the transitionValues structure when this method is called.
74     */
75    public abstract void captureValues(TransitionValues transitionValues);
76
77    /**
78     * Returns the set of property names stored in the {@link TransitionValues}
79     * object passed into {@link #captureValues(TransitionValues)} that
80     * this transition propagation cares about for the purposes of preventing
81     * duplicate capturing of property values.
82     *
83     * <p>A <code>TransitionPropagation</code> must override this method to prevent
84     * duplicate capturing of values and must contain at least one </p>
85     *
86     * @return An array of property names as described in the class documentation for
87     * {@link TransitionValues}.
88     */
89    public abstract String[] getPropagationProperties();
90
91}
92