transition/src/android/support/transition/Fade.java

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.support.transition;

import android.animation.Animator;
import android.os.Build;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.view.View;
import android.view.ViewGroup;

/**
 * This transition tracks changes to the visibility of target views in the
 * start and end scenes and fades views in or out when they become visible
 * or non-visible. Visibility is determined by both the
 * {@link View#setVisibility(int)} state of the view as well as whether it
 * is parented in the current view hierarchy.
 *
 * <p>The ability of this transition to fade out a particular view, and the
 * way that that fading operation takes place, is based on
 * the situation of the view in the view hierarchy. For example, if a view was
 * simply removed from its parent, then the view will be added into a {@link
 * android.view.ViewGroupOverlay} while fading. If a visible view is
 * changed to be {@link View#GONE} or {@link View#INVISIBLE}, then the
 * visibility will be changed to {@link View#VISIBLE} for the duration of
 * the animation. However, if a view is in a hierarchy which is also altering
 * its visibility, the situation can be more complicated. In general, if a
 * view that is no longer in the hierarchy in the end scene still has a
 * parent (so its parent hierarchy was removed, but it was not removed from
 * its parent), then it will be left alone to avoid side-effects from
 * improperly removing it from its parent. The only exception to this is if
 * the previous {@link Scene} was
 * {@link Scene#getSceneForLayout(android.view.ViewGroup, int, android.content.Context)
 * created from a layout resource file}, then it is considered safe to un-parent
 * the starting scene view in order to fade it out.</p>
 *
 * <p>Unlike the platform version, this does not support use in XML resources.</p>
 */
public class Fade extends Transition {

    /**
     * Fading mode used in {@link #Fade(int)} to make the transition
     * operate on targets that are appearing. Maybe be combined with
     * {@link #OUT} to fade both in and out.
     */
    public static final int IN = 0x1;

    /**
     * Fading mode used in {@link #Fade(int)} to make the transition
     * operate on targets that are disappearing. Maybe be combined with
     * {@link #IN} to fade both in and out.
     */
    public static final int OUT = 0x2;

    /**
     * Constructs a Fade transition that will fade targets in
     * and/or out, according to the value of fadingMode.
     *
     * @param fadingMode The behavior of this transition, a combination of
     *                   {@link #IN} and {@link #OUT}.
     */
    public Fade(int fadingMode) {
        super(true);
        if (Build.VERSION.SDK_INT < 19) {
            if (fadingMode < 0) {
                mImpl = new FadeIcs(this, fadingMode);
            } else {
                mImpl = new FadeIcs(this);
            }
        } else {
            if (fadingMode < 0) {
                mImpl = new FadeKitKat(this, fadingMode);
            } else {
                mImpl = new FadeKitKat(this);
            }
        }
    }

    /**
     * Constructs a Fade transition that will fade targets in and out.
     */
    public Fade() {
        this(-1);
    }

    @Override
    public void captureEndValues(@NonNull TransitionValues transitionValues) {
        mImpl.captureEndValues(transitionValues);
    }

    @Override
    public void captureStartValues(@NonNull TransitionValues transitionValues) {
        mImpl.captureStartValues(transitionValues);
    }

    @Override
    @Nullable
    public Animator createAnimator(@NonNull ViewGroup sceneRoot,
            @NonNull TransitionValues startValues, @NonNull TransitionValues endValues) {
        return mImpl.createAnimator(sceneRoot, startValues, endValues);
    }

}