ParallaxTarget.java revision 05de4b68e45fc22c867d49ab88e2bdfd599bf7cc 
1/*
2 * Copyright (C) 2016 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5 * in compliance with the License. You may obtain a copy of the License at
6 *
7 * http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software distributed under the License
10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11 * or implied. See the License for the specific language governing permissions and limitations under
12 * the License.
13 */
14package android.support.v17.leanback.widget;
15
16import android.animation.ObjectAnimator;
17import android.animation.PropertyValuesHolder;
18
19import java.util.List;
20
21/**
22 * ParallaxTarget is reponsible for updating the target through the {@link #update(float)} method.
23 * {@link ParallaxEffect} transforms the values of {@link ParallaxSource}, which represents the
24 * current state of UI, into a float value between 0 and 1. That float value is passed into
25 * {@link #update(float)} method.
26 */
27public abstract class ParallaxTarget {
28
29    /**
30     * Implementation class is supposed to update target with the provided fraction
31     * (between 0 and 1). The fraction represents percentage of completed change (e.g. scroll) on
32     * target.
33     *
34     * @param fraction Fraction between 0 to 1.
35     */
36    public abstract void update(float fraction);
37
38    /**
39     * Returns the current fraction (between 0 and 1). The fraction represents percentage of
40     * completed change (e.g. scroll) on target.
41     *
42     * @return Current fraction value.
43     */
44    public abstract float getFraction();
45
46    /**
47     * PropertyValuesHolderTarget is an implementation of {@link ParallaxTarget} that uses
48     * {@link PropertyValuesHolder} to update the target object.
49     */
50    public static final class PropertyValuesHolderTarget extends ParallaxTarget {
51
52        /**
53         * We simulate a parallax effect on target object using an ObjectAnimator. PSEUDO_DURATION
54         * is used on the ObjectAnimator.
55         */
56        private static final long PSEUDO_DURATION = 1000000;
57
58        private final ObjectAnimator mAnimator;
59        private float mFraction;
60
61        public PropertyValuesHolderTarget(Object targetObject, PropertyValuesHolder values) {
62            mAnimator = ObjectAnimator.ofPropertyValuesHolder(targetObject, values);
63            mAnimator.setDuration(PSEUDO_DURATION);
64        }
65
66        @Override
67        public void update(float fraction) {
68            mFraction = fraction;
69            mAnimator.setCurrentPlayTime((long) (PSEUDO_DURATION * fraction));
70        }
71
72        @Override
73        public float getFraction() {
74            return mFraction;
75        }
76    }
77}
78