NotificationPlayer.java

定義一個播放Notification聲音的player，本質上仍然是一個MediaPlayer，這個是多線程編程的很好的例子

public?class?NotificationPlayer?implements?OnCompletionListener?{

//發送播放和停止的cmd

private?static?final?int?PLAY?=?1;

private?static?final?int?STOP?=?2;

//對于多線程處理來說，這個class用來線程之間傳遞數據

private?static?final?class?Command?{

int?code;

Context?context;

Uri?uri;

boolean?looping;

int?stream;

long?requestTime;

public?String?toString()?{

return?"{?code="?+?code?+?"?looping="?+?looping?+?"?stream="?+?stream

+?"?uri="?+?uri?+?"?}";

}

}

//播放類構造函數

public?NotificationPlayer(String?tag)?{

if?(tag?!=?null)?{

mTag?=?tag;

}?else?{

mTag?=?"NotificationPlayer";

}

}

public?void?play(Context?context,?Uri?uri,?boolean?looping,?int?stream)?{

//創建用于進程之間傳遞數據的類。前面說的那個中間class

Command?cmd?=?new?Command();

//初始化信息

cmd.requestTime?=?SystemClock.uptimeMillis();

cmd.code?=?PLAY;

cmd.context?=?context;

cmd.uri?=?uri;

cmd.looping?=?looping;

cmd.stream?=?stream;

synchronized?(mCmdQueue)?{

//開始另外一個線程，用來解析用戶設置cmd，然后才決定是play還是stop

enqueueLocked(cmd);

mState?=?PLAY;

}

}

//這表明CmdThread就是一個thread

private?final?class?CmdThread?extends?java.lang.Thread?{

CmdThread()?{

super("NotificationPlayer-"?+?mTag);

}

public?void?run()?{

while?(true)?{

Command?cmd?=?null;

synchronized?(mCmdQueue)?{

//這一步很巧妙，直接用隊列中刪除返回刪除數據的引用來獲取剛才在play中設置的信息

cmd?=?mCmdQueue.removeFirst();

}

switch?(cmd.code)?{

case?PLAY:

startSound(cmd);

break;

//主要是用戶發出停止的命令的操作--非正常播放結束stop

case?STOP:

……

//強制停止要釋放focus

mAudioManager.abandonAudioFocus(null);

break;

}

//處理之后要釋放wakelock

synchronized?(mCmdQueue)?{

if?(mCmdQueue.size()?==?0)?{

mThread?=?null;

releaseWakeLock();

return;

}

}

}

}

}//end?ofCmdThread

private?void?startSound(Command?cmd)?{

try?{

if((mLooper?!=?null)

&&?(mLooper.getThread().getState()?!=?Thread.State.TERMINATED))?{

mLooper.quit();

}

mCompletionThread?=?new?CreationAndCompletionThread(cmd);

//開啟播放線程

synchronized(mCompletionThread)?{

mCompletionThread.start();

mCompletionThread.wait();

}

}

}

private?final?class?CreationAndCompletionThread?extends?Thread?{

public?Command?mCmd;

public?CreationAndCompletionThread(Command?cmd)?{

super();

mCmd?=?cmd;

}

public?void?run()?{

try?{

//設置播放信息，并開始播放

MediaPlayer?player?=?new?MediaPlayer();

player.setAudioStreamType(mCmd.stream);

player.setDataSource(mCmd.context,?mCmd.uri);

player.setLooping(mCmd.looping);

player.prepare();

if?((mCmd.uri?!=?null)?&&?(mCmd.uri.getEncodedPath()?!=?null)

&&?(mCmd.uri.getEncodedPath().length()?>?0))?{

if?(mCmd.looping)?{

audioManager.requestAudioFocus(null,?mCmd.stream,

AudioManager.AUDIOFOCUS_GAIN);

}?else?{

audioManager.requestAudioFocus(null,?mCmd.stream,

AudioManager.AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK);

}

}

//這一步是必須的，要釋放focus

player.setOnCompletionListener(NotificationPlayer.this);

player.start();

}

}

}

public?void?onCompletion(MediaPlayer?mp)?{

if?(mAudioManager?!=?null)?{

mAudioManager.abandonAudioFocus(null);

}

}

}

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