/**
 * 來電靜音
 *
 * @param context
 */
private void toggleRingerMute(Context context)
{
    AudioManager am = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
    if (previousMuteMode == -1)
    {
        previousMuteMode = am.getRingerMode();
        am.setRingerMode(0);
    }
    am.setRingerMode(previousMuteMode);
    previousMuteMode = -1;
}