播放一个声音

 // Do the common stuff when starting the alarm.
    private void startAlarm(MediaPlayer player)
            throws java.io.IOException, IllegalArgumentException,
                   IllegalStateException {
        final AudioManager audioManager = (AudioManager)getSystemService(Context.AUDIO_SERVICE);
        // do not play alarms if stream volume is 0
        // (typically because ringer mode is silent).
        if (audioManager.getStreamVolume(AudioManager.STREAM_ALARM) != 0) {
            player.setAudioStreamType(AudioManager.STREAM_ALARM);
            player.setLooping(true);
            player.prepare();
            player.start();
        }
    }

    private void setDataSourceFromResource(Resources resources,
            MediaPlayer player, int res) throws java.io.IOException {
        AssetFileDescriptor afd = resources.openRawResourceFd(res);
        if (afd != null) {
            player.setDataSource(afd.getFileDescriptor(), afd.getStartOffset(),
                    afd.getLength());
            afd.close();
        }
    }

private static final float IN_CALL_VOLUME = 0.125f;

 // Check if we are in a call. If we are, use the in-call alarm
                // resource at a low volume to not disrupt the call.
                if (mTelephonyManager.getCallState()
                        != TelephonyManager.CALL_STATE_IDLE) {
                    Log.v("Using the in-call alarm");
                    mMediaPlayer.setVolume(IN_CALL_VOLUME, IN_CALL_VOLUME);
                    setDataSourceFromResource(getResources(), mMediaPlayer,
                            R.raw.in_call_alarm);
                } else {
                    mMediaPlayer.setDataSource(this, alert);
                }
                startAlarm(mMediaPlayer);