RemoteControlClient的使用

 RemoteControlClient是从API 14也就是android 4.0开始出现的类，用于在锁屏状态控制音乐播放。界面是系统提供的。

api doc文档上附了一段注册代码

ComponentName myEventReceiver = new ComponentName(getPackageName(), MyRemoteControlEventReceiver.class.getName());
 AudioManager myAudioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
 myAudioManager.registerMediaButtonEventReceiver(myEventReceiver);
 // build the PendingIntent for the remote control client
 Intent mediaButtonIntent = new Intent(Intent.ACTION_MEDIA_BUTTON);
 mediaButtonIntent.setComponent(myEventReceiver);
 PendingIntent mediaPendingIntent = PendingIntent.getBroadcast(getApplicationContext(), 0, mediaButtonIntent, 0);
 // create and register the remote control client
 RemoteControlClient myRemoteControlClient = new RemoteControlClient(mediaPendingIntent);
 myAudioManager.registerRemoteControlClient(myRemoteControlClient);

上面的代码开始时注册了耳机按键的事件，接着注册了RemoteControlClient。

要想弄出RemoteControlClient的界面，上面的代码还不够，还需要把当前音乐状态设置为正在播放

mClient.setPlaybackState(RemoteControlClient.PLAYSTATE_PLAYING)

并且必须获取当前的stream focus

		am.requestAudioFocus(new OnAudioFocusChangeListener() {
			
			@Override
			public void onAudioFocusChange(int focusChange) {
				System.out.println("focusChange = " + focusChange);
			}
		}, AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN);

这样，在锁屏状态系统界面就能出现了，默认只有一个播放暂停按钮。要想显示额外的信息，使用editMetadata(boolean startEmpty)去put，如果想多显示几个控制按钮，如下：

        int flags = RemoteControlClient.FLAG_KEY_MEDIA_PREVIOUS
                | RemoteControlClient.FLAG_KEY_MEDIA_NEXT
                | RemoteControlClient.FLAG_KEY_MEDIA_PLAY
                | RemoteControlClient.FLAG_KEY_MEDIA_PAUSE
                | RemoteControlClient.FLAG_KEY_MEDIA_PLAY_PAUSE
                | RemoteControlClient.FLAG_KEY_MEDIA_STOP;
        mClient.setTransportControlFlags(flags);

所有按键的响应事件都在注册的receiver中。