通过广播Intent控制Android系统自带的音乐播放器

通过广播Intent控制Android系统自带的音乐播放器

ZhengZhiren
http://blog.csdn.net/ZhengZhiRen/archive/2011/01/13/6134730.aspx

Android自带的音乐播放器只能算是系统之上的应用，并不包含在SDK中，因此SDK文档中没有提及。但是，有时我们需要控制系统音乐播放器的行为，比如切换歌曲、暂停/继续等。这就只能从这个应用的源代码着手了。

这是播放器的代码树：
http://android.git.kernel.org/?p=platform/packages/apps/Music.git;a=tree

可以看到，音乐的播放是由MediaPlaybackService这个服务实现的：
http://android.git.kernel.org/?p=platform/packages/apps/Music.git;a=blob;f=src/com/android/music/MediaPlaybackService.java;h=7c0bbedbedef49bf4c38ef97fdcd0f1017bf5d35;hb=HEAD

在服务的onCreate函数中，注册了IntentFilter和BroadcastReceiver。

public void onCreate() {
super.onCreate();
……
IntentFilter commandFilter = new IntentFilter();
commandFilter.addAction(SERVICECMD);
commandFilter.addAction(TOGGLEPAUSE_ACTION);
commandFilter.addAction(PAUSE_ACTION);
commandFilter.addAction(NEXT_ACTION);
commandFilter.addAction(PREVIOUS_ACTION);
registerReceiver(mIntentReceiver, commandFilter);
……
}

这些Action常量在类的开头定义为：

public static final String SERVICECMD = "com.android.music.musicservicecommand";
public static final String CMDNAME = "command";
public static final String CMDTOGGLEPAUSE = "togglepause";
public static final String CMDSTOP = "stop";
public static final String CMDPAUSE = "pause";
public static final String CMDPREVIOUS = "previous";
public static final String CMDNEXT = "next";
public static final String TOGGLEPAUSE_ACTION = "com.android.music.musicservicecommand.togglepause";
public static final String PAUSE_ACTION = "com.android.music.musicservicecommand.pause";
public static final String PREVIOUS_ACTION = "com.android.music.musicservicecommand.previous";
public static final String NEXT_ACTION = "com.android.music.musicservicecommand.next";

BroadcastReceiver接收和IntentFilter匹配的Intent。根据intent.getAction或intent.getStringExtra("command")的内容，进行相应操作，控制播放器的播放。

private BroadcastReceiver mIntentReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
String cmd = intent.getStringExtra("command");
MusicUtils.debugLog("mIntentReceiver.onReceive " + action + " / " + cmd);
if (CMDNEXT.equals(cmd) || NEXT_ACTION.equals(action)) {
next(true);
} else if (CMDPREVIOUS.equals(cmd) || PREVIOUS_ACTION.equals(action)) {
prev();
} else if (CMDTOGGLEPAUSE.equals(cmd) || TOGGLEPAUSE_ACTION.equals(action)) {
if (isPlaying()) {
pause();
mPausedByTransientLossOfFocus = false;
} else {
play();
}
} else if (CMDPAUSE.equals(cmd) || PAUSE_ACTION.equals(action)) {
pause();
mPausedByTransientLossOfFocus = false;
} else if (CMDSTOP.equals(cmd)) {
pause();
mPausedByTransientLossOfFocus = false;
seek(0);
} else if (MediaAppWidgetProvider.CMDAPPWIDGETUPDATE.equals(cmd)) {
// Someone asked us to refresh a set of specific widgets, probably
// because they were just added.
int[] appWidgetIds = intent.getIntArrayExtra(AppWidgetManager.EXTRA_APPWIDGET_IDS);
mAppWidgetProvider.performUpdate(MediaPlaybackService.this, appWidgetIds);
}
}
};

由此，我们可以通过广播intent控制播放器了：

Intent intent = new Intent("上面那几个常量");
sendBroadcast(intent);

参考资料：
http://www.poemcode.net/2009/11/android_music/
http://android.git.kernel.org/?p=platform/packages/apps/Music.git;a=tree