Android实现监听音量的变化

@Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        switch (keyCode) {
            case KeyEvent.KEYCODE_VOLUME_UP:
                //音量键up
                return false;
            case KeyEvent.KEYCODE_VOLUME_DOWN:
                //音量键down
                return false;
            default:
                break;
        }
        return super.onKeyDown(keyCode, event);
}

class VolumeChangeHelper(var context: Context){

    private var mVolumeBroadCastReceiver: VolumeBroadCastReceiver&＃63; = null
    private var mVolumeChangeListener: VolumeChangeListener&＃63; = null

    companion object{
        const val  VOLUME_CHANGE_ACTION = "android.media.VOLUME_CHANGED_ACTION"
        const val EXTRA_VOLUME_STREAM_TYPE = "android.media.EXTRA_VOLUME_STREAM_TYPE"
    }

    private var audioManager: AudioManager&＃63; =  context.getSystemService(Context.AUDIO_SERVICE) as&＃63; AudioManager

    fun registerVolumeChangeListener(volumeChangeListener: VolumeChangeListener){
        mVolumeChangeListener = volumeChangeListener
        mVolumeBroadCastReceiver = VolumeBroadCastReceiver()
        val filter = IntentFilter()
        filter.addAction(VOLUME_CHANGE_ACTION)
        if(mVolumeBroadCastReceiver != null){
            //注册这个广播
            context.registerReceiver(mVolumeBroadCastReceiver!!, filter)
        }
    }

    fun unregisterReceiver(){
        if(mVolumeBroadCastReceiver != null){
            context.unregisterReceiver(mVolumeBroadCastReceiver!!)
            mVolumeBroadCastReceiver = null
        }
    }

    interface VolumeChangeListener{
        fun onVolumeDownToMin()
        fun onVolumeUp()
    }
    
    //定义一个想监听音量变化的广播接受者
    inner class VolumeBroadCastReceiver : BroadcastReceiver(){
        override fun onReceive(context: Context&＃63;, intent: Intent&＃63;) {
            if(intent&＃63;.action == VOLUME_CHANGE_ACTION && intent&＃63;.getIntExtra(EXTRA_VOLUME_STREAM_TYPE, -1) == AudioManager.STREAM_MUSIC){
                val currentVolume = audioManager&＃63;.getStreamVolume(AudioManager.STREAM_MUSIC) &＃63;: -1
                if(currentVolume > 0){
                    mVolumeChangeListener&＃63;.onVolumeUp()
                } else  if( currentVolume == 0){
                    mVolumeChangeListener&＃63;.onVolumeDownToMin()
                }
            }
        }

    }
}