Android13 MediaPlayer 创建流程分析

MediaPlayer可以通过两种方法进行创建。

方法一：通过new一个MediaPlayer对象的方法进行创建，MediaPlayer的构造函数如下：

方法二：通过MediaPlayer的create方法进行创建。

通过new一个MediaPlayer对象的方法进行创建

MediaPlayer的构造函数如下：

//frameworks/base/media/java/android/media/MediaPlayer.java
public class MediaPlayer extends PlayerBase implements SubtitleController.Listener, VolumeAutomation, AudioRouting
{
    public MediaPlayer() {
        this(AudioSystem.AUDIO_SESSION_ALLOCATE);
    }
}

调用重载方法：

//frameworks/base/media/java/android/media/MediaPlayer.java
public class MediaPlayer extends PlayerBase implements SubtitleController.Listener, VolumeAutomation, AudioRouting
{
    private MediaPlayer(int sessionId) {
        super(new AudioAttributes.Builder().build(),
                AudioPlaybackConfiguration.PLAYER_TYPE_JAM_MEDIAPLAYER);


        Looper looper;
        if ((looper = Looper.myLooper()) != null) {
            mEventHandler = new EventHandler(this, looper); //创建EventHandler对象，用于处理消息
        } else if ((looper = Looper.getMainLooper()) != null) {
            mEventHandler = new EventHandler(this, looper); //创建EventHandler对象，用于处理消息
        } else {
            mEventHandler = null;
        }


        mTimeProvider = new TimeProvider(this); 
        mOpenSubtitleSources = new Vector<InputStream>();


        AttributionSource attributionSource = AttributionSource.myAttributionSource();
        // set the package name to empty if it was null
        if (attributionSource.getPackageName() == null) {
            attributionSource = attributionSource.withPackageName("");
        }


        /* Native setup requires a weak reference to our object.
         * It's easier to create it here than in C++.
         */
        try (ScopedParcelState attributionSourceState = attributionSource.asScopedParcelState()) {
            native_setup(new WeakReference<MediaPlayer>(this), attributionSourceState.getParcel()); //调用了native_setup()函数，并传入了一个MediaPlayer类型的弱引用实例
        }


        baseRegisterPlayer(sessionId);
    }
}

构造函数中主要处理如下：

1、创建EventHandler对象

EventHandler是MediaPlayer的一个内部类，它专门处理来自Native层的事件，这些事件一般都表明了MediaPlayer现在转移到了某个状态，我们可以在该状态处理什么回调操作。EventHandler的功能较为单一，就是根据底层上抛的事件，进行对应的回调或事件处理。

2、调用了native_setup()方法，并传入了一个MediaPlayer类型的弱引用实例。

3、调用baseRegisterPlayer方法，也就是父类PlayerBase的baseRegisterPlayer方法，注册播放器。

EventHandler处理比较简单，我们在其它流程中分析，下面我们继续分析native_setup方法：

native_setup

调用native_setup会通过jni调用android_media_MediaPlayer的android_media_MediaPlayer_native_setup方法：

//frameworks/base/core/jni/android_media_MediaPlayer.cpp
static void
android_media_MediaPlayer_native_setup(JNIEnv *env, jobject thiz, jobject weak_this, jobject jAttributionSource)
{
    ALOGV("native_setup");


    Parcel* parcel = parcelForJavaObject(env, jAttributionSource);
    android::content::AttributionSourceState attributionSource;
    attributionSource.readFromParcel(parcel);
    sp<MediaPlayer> mp = sp<MediaPlayer>::make(attributionSource); //创建MediaPlayer对象
    if (mp == NULL) {
        jniThrowException(env, "java/lang/RuntimeException", "Out of memory");
        return;
    }


    // create new listener and give it to MediaPlayer
    sp<JNIMediaPlayerListener> listener = new JNIMediaPlayerListener(env, thiz, weak_this); //创建JNIMediaPlayerListener对象
    mp->setListener(listener); //在Native MediaPlayer实例中保存这个JNIMediaPlayerListener监听