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

    <receiver android:name=".CallBroadcastReceiver" >
        <intent-filter>
            <action android:name="android.media.VOLUME_CHANGED_ACTION" />
        </intent-filter>
    </receiver>
    <receiver android:name=".MyWakefulReceiver"></receiver> //deprecated.

public class MainActivity extends AppCompatActivity {

PowerManager pm;
PowerManager.WakeLock wl;
MediaButtonIntentReceiver r;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    pm = (PowerManager) getSystemService(getApplicationContext().POWER_SERVICE);
    wl = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "Tag");
    wl.acquire();
    IntentFilter filter = new IntentFilter(Intent.ACTION_MEDIA_BUTTON);
     r = new MediaButtonIntentReceiver();
    filter.setPriority(1000);
    registerReceiver(r, filter);
}
}

public class MediaButtonIntentReceiver extends BroadcastReceiver {

public MediaButtonIntentReceiver() {
    super();
}


@Override
public void onReceive(Context context, Intent intent) {
    String intentAction = intent.getAction();
    if (!Intent.ACTION_MEDIA_BUTTON.equals(intentAction)) {
        return;
    }
    KeyEvent event = intent.getParcelableExtra(Intent.EXTRA_KEY_EVENT);
    if (event == null) {
        return;
    }
    int action = event.getAction();
    if (action == KeyEvent.ACTION_DOWN) {
        // do something
        Toast.makeText(context, "BUTTON PRESSED! "+action, Toast.LENGTH_SHORT).show();
    }

    abortBroadcast();
}
}