Android小窗口模式，picture-in-picture（PIP画中画）的使用

1.介绍

Android8.0的时候推出了画中画模式，可以让Activity缩小显示在其他Activity上方。当初我维护的项目本身自己实现了这个功能，Android加入画中画之后两个功能并行，互相交互的时候出了一大堆问题。现在几乎所有的视频软件都加入了这个功能。使用方法十分简单，但是需要处理好AudioFocus的问题。

2.参数介绍

在Android 8.0时候，只需要调用Activity的
enterPictureInPictureMode();
或者enterPictureInPictureModeIfPossible() 即可

 public boolean enterPictureInPictureMode(@NonNull PictureInPictureParams params) {try {if (params == null) {throw new IllegalArgumentException("Expected non-null picture-in-picture params");}return ActivityManagerNative.getDefault().enterPictureInPictureMode(mToken, params);} catch (RemoteException e) {return false;}}

进入的时候需要传入PictureInPictureParams类型参数。
现在高版本Android已经@Deprecated enterPictureInPictureMode() 和enterPictureInPictureMode(@NonNull PictureInPictureArgs args) 这两个方法。想要使用画中画必须传入参数。

我们先看一下PictureInPictureParams 的源码

/** Copyright (C) 2017 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.app;import android.annotation.Nullable;
import android.graphics.Rect;
import android.os.Parcel;
import android.os.Parcelable;
import android.util.Rational;import java.util.ArrayList;
import java.util.List;/*** Represents a set of parameters used to initialize and update an Activity in picture-in-picture* mode.*/
public final class PictureInPictureParams implements Parcelable {/*** Builder class for {@link PictureInPictureParams} objects.*/public static class Builder {@Nullableprivate Rational mAspectRatio;@Nullableprivate List<RemoteAction> mUserActions;@Nullableprivate Rect mSourceRectHint;/*** Sets the aspect ratio. This aspect ratio is defined as the desired width / height, and* does not change upon device rotation.** @param aspectRatio the new aspect ratio for the activity in picture-in-picture, must be* between 2.39:1 and 1:2.39 (inclusive).** @return this builder instance.*/public Builder setAspectRatio(Rational aspectRatio) {mAspectRatio = aspectRatio;return this;}/*** Sets the user actions. If there are more than* {@link Activity#getMaxNumPictureInPictureActions()} actions, then the input list* will be truncated to that number.** @param actions the new actions to show in the picture-in-picture menu.** @return this builder instance.** @see RemoteAction*/public Builder setActions(List<RemoteAction> actions) {if (mUserActions != null) {mUserActions = null;}if (actions != null) {mUserActions = new ArrayList<>(actions);}return this;}/*** Sets the source bounds hint. These bounds are only used when an activity first enters* picture-in-picture, and describe the bounds in window coordinates of activity entering* picture-in-picture that will be visible following the transition. For the best effect,* these bounds should also match the aspect ratio in the arguments.** @param launchBounds window-coordinate bounds indicating the area of the activity that* will still be visible following the transition into picture-in-picture (eg. the video* view bounds in a video player)** @return this builder instance.*/public Builder setSourceRectHint(Rect launchBounds) {if (launchBounds == null) {mSourceRectHint = null;} else {mSourceRectHint = new Rect(launchBounds);}return this;}/*** @return an immutable {@link PictureInPictureParams} to be used when entering or updating* the activity in picture-in-picture.** @see Activity#enterPictureInPictureMode(PictureInPictureParams)* @see Activity#setPictureInPictureParams(PictureInPictureParams)*/public PictureInPictureParams build() {PictureInPictureParams params = new PictureInPictureParams(mAspectRatio, mUserActions,mSourceRectHint);return params;}}/*** The expected aspect ratio of the picture-in-picture.*/@Nullableprivate Rational mAspectRatio;/*** The set of actions that are associated with this activity when in picture-in-picture.*/@Nullableprivate List<RemoteAction> mUserActions;/*** The source bounds hint used when entering picture-in-picture, relative to the window bounds.* We can use this internally for the transition into picture-in-picture to ensure that a* particular source rect is visible throughout the whole transition.*/@Nullableprivate Rect mSourceRectHint;/** {@hide} */PictureInPictureParams() {}/** {@hide} */PictureInPictureParams(Parcel in) {if (in.readInt() != 0) {mAspectRatio = new Rational(in.readInt(), in.readInt());}if (in.readInt() != 0) {mUserActions = new ArrayList<>();in.readParcelableList(mUserActions, RemoteAction.class.getClassLoader());}if (in.readInt() != 0) {mSourceRectHint = Rect.CREATOR.createFromParcel(in);}}/** {@hide} */PictureInPictureParams(Rational aspectRatio, List<RemoteAction> actions,Rect sourceRectHint) {mAspectRatio = aspectRatio;mUserActions = actions;mSourceRectHint = sourceRectHint;}/*** Copies the set parameters from the other picture-in-picture args.* @hide*/public void copyOnlySet(PictureInPictureParams otherArgs) {if (otherArgs.hasSetAspectRatio()) {mAspectRatio = otherArgs.mAspectRatio;}if (otherArgs.hasSetActions()) {mUserActions = otherArgs.mUserActions;}if (otherArgs.hasSourceBoundsHint()) {mSourceRectHint = new Rect(otherArgs.getSourceRectHint());}}/*** @return the aspect ratio. If none is set, return 0.* @hide*/public float getAspectRatio() {if (mAspectRatio != null) {return mAspectRatio.floatValue();}return 0f;}/** @hide */public Rational getAspectRatioRational() {return mAspectRatio;}/*** @return whether the aspect ratio is set.* @hide*/public boolean hasSetAspectRatio() {return mAspectRatio != null;}/*** @return the set of user actions.* @hide*/public List<RemoteAction> getActions() {return mUserActions;}/*** @return whether the user actions are set.* @hide*/public boolean hasSetActions() {return mUserActions != null;}/*** Truncates the set of actions to the given {@param size}.* @hide*/public void truncateActions(int size) {if (hasSetActions()) {mUserActions = mUserActions.subList(0, Math.min(mUserActions.size(), size));}}/*** @return the source rect hint* @hide*/public Rect getSourceRectHint() {return mSourceRectHint;}/*** @return whether there are launch bounds set* @hide*/public boolean hasSourceBoundsHint() {return mSourceRectHint != null && !mSourceRectHint.isEmpty();}@Overridepublic int describeContents() {return 0;}@Overridepublic void writeToParcel(Parcel out, int flags) {if (mAspectRatio != null) {out.writeInt(1);out.writeInt(mAspectRatio.getNumerator());out.writeInt(mAspectRatio.getDenominator());} else {out.writeInt(0);}if (mUserActions != null) {out.writeInt(1);out.writeParcelableList(mUserActions, 0);} else {out.writeInt(0);}if (mSourceRectHint != null) {out.writeInt(1);mSourceRectHint.writeToParcel(out, 0);} else {out.writeInt(0);}}public static final Creator<PictureInPictureParams> CREATOR =new Creator<PictureInPictureParams>() {public PictureInPictureParams createFromParcel(Parcel in) {return new PictureInPictureParams(in);}public PictureInPictureParams[] newArray(int size) {return new PictureInPictureParams[size];}};
}

可以看到PictureInPictureParams是使用链式调用的建造者模式设计的，他的主要成员有
mAspectRatio ：

/*** Sets the aspect ratio. This aspect ratio is defined as the desired width / height, and* does not change upon device rotation.** @param aspectRatio the new aspect ratio for the activity in picture-in-picture, must be* between 2.39:1 and 1:2.39 (inclusive).** @return this builder instance.*/

高宽比，比例限定在2.39:1到1:2.39之间。

mUserActions ：

     /*** Sets the user actions. If there are more than* {@link Activity#getMaxNumPictureInPictureActions()} actions, then the input list* will be truncated to that number.** @param actions the new actions to show in the picture-in-picture menu.** @return this builder instance.** @see RemoteAction*/

Action是一种控件，早期版本的Android GMS Setting中的item就是由Action组成的。
这里的userAction是RemoteAction类型，这个类型和Action没哟US很么关系，但是是类似的东西，它是一个可序列化的对象，具体成员为

 	private final Icon mIcon;private final CharSequence mTitle;private final CharSequence mContentDescription;private final PendingIntent mActionIntent;private boolean mEnabled;

具体代码可看RemoteAction.java

简单来说这个就是当Activity进入画中画之后缩小的Activity下方会显示一个类似Android导航栏的东西，由几个按键组成，每个按键就是一个RemoteAction。将这个RemoteAction 列表在放入PictureInPictureParams参数中进入画中画的时候这些按钮就会显示。但是在手机端一般不需要，这几个键的功能一般是回到全屏显示，关闭画中画小窗口，切换小窗口大小，位置这种功能，一般手机端的APP只需要双击小窗口回到全屏这个功能。但是Android TV端是需要的，因为TV一般没有触摸屏，全靠遥控器，走的是onKey事件，需要使用按键来切换获得焦点的控件。

这里比较重要的是mActionIntent，这是一个PendingIntent类型的对象。这个PendingIntent定义了RemoteAction被触发后的行为。PendingIntent可以看作是对Intent的一个封装，但它不是立刻执行某个行为。可以使用getActivity, getActivities, getBroadcast, and getService方法获取可以启动Activity或者发送广播开启服务的PendingIntent对象。

PendingIntent官方文档

mSourceRectHint ：

 /*** Sets the source bounds hint. These bounds are only used when an activity first enters* picture-in-picture, and describe the bounds in window coordinates of activity entering* picture-in-picture that will be visible following the transition. For the best effect,* these bounds should also match the aspect ratio in the arguments.** @param launchBounds window-coordinate bounds indicating the area of the activity that* will still be visible following the transition into picture-in-picture (eg. the video* view bounds in a video player)** @return this builder instance.*/

边界约束
官方文档上的介绍是

每个单词我都知道什么意思，但是我感觉它讲的不是人话。

大概意思是说Activity在进入画中画模式之后因为变小了，宽高比又可能和原先屏幕不同，所以有些画面显示不出来，设定一个区域。这个区域在进入画中画缩小了之后依然可见。这个区域要和前面设置的高宽比对应，这样才能显示的比较好。（我猜的）

然后我在代码中设置各种Rect的值发现对PIP叼影响都没有，根本猜不到这玩意干吗的。这叼文档不讲人话，代码也没效果，我真不知道这玩意干吗的，有知道的大神麻烦指点一下。

3.使用

最早的时候使用十分简单。
直接调用Activity的

  @Overridepublic void enterPictureInPictureModeIfPossible() {if (mActivityInfo.supportsPictureInPicture()) {enterPictureInPictureMode();}}

就可以了。现在这个API没法调用了，可以通过

 @Deprecatedpublic void enterPictureInPictureMode() {enterPictureInPictureMode(new PictureInPictureParams.Builder().build());}

进入PIP，但是和上面那个API相比，如果你的Activity不支持PIP模式，会报异常出来。
所以你需要在清单文件中加上这样一句话

 android:supportsPictureInPicture="true"android:configChanges="screenSize|smallestScreenSize|screenLayout|orientation"

我在Activity中创建一个Button，点击这个Button调用enterPictureInPictureMode()

点击之后的效果

再单击一次小窗口

但是这个方法毕竟被Deprecated了，目前API28上还可以使用，说不定下个版本这个API就被取消了。

所以我们还是需要学会使用带有PictureInPictureParams 参数的
enterPictureInPictureMode(@NonNull PictureInPictureParams params) 方法

 Icon icon = Icon.createWithResource(mContext, R.mipmap.ic_launcher);Icon icon2 = Icon.createWithResource(mContext,R.mipmap.ic_launcher_round);Intent intent = new Intent(this, MainActivity.class);PendingIntent pendingIntent = PendingIntent.getActivity(mContext, 998, intent, PendingIntent.FLAG_ONE_SHOT);RemoteAction remoteAction = new RemoteAction(icon, "标题", "介绍", pendingIntent);RemoteAction remoteAction2 = new RemoteAction(icon2, "标题2", "介绍2", pendingIntent);ArrayList<RemoteAction> arrayList = new ArrayList<RemoteAction>();arrayList.add(remoteAction);arrayList.add(remoteAction2);Rational rational = new Rational(3, 7);//这里如果设置的值太大或者太小或报异常Rect rect = new Rect(0, 0, 0, 0);final PictureInPictureParams params = new PictureInPictureParams.Builder().setActions(arrayList).setAspectRatio(rational).setSourceRectHint(rect).build();button.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {
// enterPictureInPictureMode();enterPictureInPictureMode(params);}});

Rational的比值需要在2.39:1到1:2.39之间否则

java.lang.IllegalArgumentException: enterPictureInPictureMode: Aspect ratio is too extreme (must be between 0.418410 and 2.390000).

效果：

单击小窗口后

可以看到有2个按钮，这就是我们设置的RemoteAction，点击后会触发PendingIntent。
中间的按钮是自带的最大化按钮，右上角也是自带的关闭按钮，左上为自带的设置按钮，这个在不同版本的Android上还有Android TV上都可能不相同。

哎刚准备讲改变小窗口size的，我记得Android 8.0 拿到beta版本的时候还是可以调节小窗口大小的，有3种size，结果现在用最新的AndroidQ已经不能调节了，不知道google又改了啥。然后我用EMUI10看b站和斗鱼都找不到PIP入口图标了，优酷和爱奇艺可以进入PIP,但是也不能调节小窗口大小。

言归正传，可以看到进入小窗口后显示的比例和原屏幕比例不一样，所以有的内容显示不出来，这个时候需要对UI进行调节。

比如你播放视频的话，你可以先让Video全屏播放，或者干脆全屏播放的时候才提供PIP入口，然后设置视频对应的Rational给PIP,也就是说在进入PIP前和退出PIP后是需要做一些页面调整的，而且比如你有计算UI坐标或者动态修改控件位置的逻辑，在进入PIP之前都需要处理掉，回到正常模式再还原，否则进入PIP之后再去获取这些就不准确了，整个UI会乱掉。
之前PIP功能刚上的时候QA给我开了很多这样的BUG。

现在还提供了了onPictureInPictureModeChanged()回调

  @Overridepublic void onPictureInPictureModeChanged(boolean isInPictureInPictureMode, Configuration newConfig) {super.onPictureInPictureModeChanged(isInPictureInPictureMode, newConfig);if (isInPictureInPictureMode){}else {}}

可以在这里处理PIP进入和退出的逻辑。禁用一些UI或者干脆给PIP模式加载一套新的layout。

4.注意

一些需要注意的点
首先一个Activity进入PIP的时候，缩小在其他应用上方显示，这个时候生命周期是走到了onPause(),但是没有走到OnStop(),这个有点像以前的VisibleBehind模式下的Activity生命周期。所以如果你在onPause的时候暂停播放，进入画中画之后就不会播放了。

AudioFocus问题，在8.0的时候我看到很多app小窗口的时候会去抢AudioFocus,我记得我曾经开了3个小窗口可以同时播放视频，还都有声音。但是现在的版本不行了，同时只有一个APP能获取到AudioFocus，而且主页面播放视频小窗口会自动暂停,而且同一时间也只能存活一个PIP进程。