当按下耳机按钮时，在Android API中生成KEYCODE_MEDIA_PLAY_PAUSE＆gt; 21？

Question

我正在尝试获取处理ACTION_MEDIA_BUTTON Intent的keyCodes。我正在研究API＆gt; 21，下面是我的代码。每次按下耳机按钮，我都会收到keyCode = KEYCODE_HEADSETHOOK。有人可以告诉我何时会收到KEYCODE_MEDIA_PLAY_PAUSE或KEYCODE_MEDIA_NEXT或任何其他与MEDIA相关的keyCode。

public class MainActivity extends Activity {


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    setVolumeControlStream(AudioManager.STREAM_MUSIC);
    final MediaSession session = new MediaSession(getApplicationContext(), "TRIGGER");
    session.setFlags(MediaSession.FLAG_HANDLES_MEDIA_BUTTONS | MediaSession.FLAG_HANDLES_TRANSPORT_CONTROLS);
    session.setActive(true);
    PlaybackState state = new PlaybackState.Builder()
            .setActions(PlaybackState.ACTION_PLAY | PlaybackState.ACTION_PLAY_PAUSE |
                            PlaybackState.ACTION_PLAY_FROM_MEDIA_ID | PlaybackState.ACTION_PAUSE |
                            PlaybackState.ACTION_SKIP_TO_NEXT | PlaybackState.ACTION_SKIP_TO_PREVIOUS)
            .setState(PlaybackState.STATE_PLAYING, 1, 2, SystemClock.elapsedRealtime())
            .build();
    session.setPlaybackState(state);


    session.setCallback(new MediaSession.Callback() {
        @Override
        public boolean onMediaButtonEvent(final Intent mediaButtonIntent) {

            String intentAction = mediaButtonIntent.getAction();

            if (Intent.ACTION_MEDIA_BUTTON.equals(intentAction))
            {
                KeyEvent event = (KeyEvent)mediaButtonIntent.getParcelableExtra(Intent.EXTRA_KEY_EVENT);
                if (event != null)
                {
                    int action = event.getAction();
                    int code = event.getKeyCode();
                    if (action == KeyEvent.ACTION_DOWN) {
                        Log.i("TRIGGER", "EVENT RECEIVED");
                        Log.i("TRIGGER", String.valueOf(event));
                        Log.i("TRIGGER", String.valueOf(action));
                        Log.i("TRIGGER", String.valueOf(code));
                    }
                }

            }
           return super.onMediaButtonEvent(mediaButtonIntent);
        }


    });

}

清单文件中也提到了Intent过滤器，如下所示。

<intent-filter>
            <action android:name="android.intent.action.MEDIA_BUTTON" />
        </intent-filter>

按下耳机按钮时的LogCat详细信息。

09-11 17:39:42.134  15765-15789/com.example.amit.myapplication I/OpenGLRenderer﹕ Initialized EGL, version 1.4
09-11 17:39:42.147  15765-15789/com.example.amit.myapplication D/OpenGLRenderer﹕ Enabling debug mode 0
09-11 17:39:46.843  15765-15765/com.example.amit.myapplication I/TRIGGER﹕ EVENT RECEIVED
09-11 17:39:46.843  15765-15765/com.example.amit.myapplication I/TRIGGER﹕ KeyEvent { action=ACTION_DOWN, keyCode=KEYCODE_HEADSETHOOK, scanCode=226, metaState=0, flags=0x8, repeatCount=0, eventTime=217783805, downTime=217783641, deviceId=4, source=0x101 }
09-11 17:39:46.843  15765-15765/com.example.amit.myapplication I/TRIGGER﹕ 0
09-11 17:39:46.843  15765-15765/com.example.amit.myapplication I/TRIGGER﹕ 79