Android 当源为空时，如何在exoplayer中显示脱机消息

我需要捕获exoplayer在没有输入或坏流时抛出的错误。如果没有显示带有控件的播放器的输入活动打开，则不会显示任何内容。当没有输入hls源时，我需要显示流媒体脱机的警报对话框。如何做到这一点。请帮忙

class playlive : AppCompatActivity() {

    private var player: SimpleExoPlayer? = null
    private var playerView: PlayerView? = null
    private var playWhenReady = true

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_playlive)
        playerView = findViewById(R.id.player_view)


        play()

    }

private fun play(){

        val trackSelector = DefaultTrackSelector()
        trackSelector.setParameters(trackSelector.buildUponParameters().setMaxVideoSizeSd())
        player = ExoPlayerFactory.newSimpleInstance(this, trackSelector)

    playerView!!.player = player
    val dataSourceFactory = DefaultHttpDataSourceFactory(Util.getUserAgent(this, "app-name"))
    val uri = Uri.parse("http://localhost:1935/live/mystream/index.m3u8")
    val hlsMediaSource = HlsMediaSource.Factory(dataSourceFactory).createMediaSource(uri)

    player!!.playWhenReady = playWhenReady
    player!!.prepare(hlsMediaSource)

}
    override fun onStop() {
        super.onStop()
        releasePlayer()

    }

    override fun onResume() {
        super.onResume()
        releasePlayer()
        resumePlayer()
    }

    override fun onDestroy() {
        super.onDestroy()
        releasePlayer()

    }

    private fun releasePlayer(){
        player?.release()
    }

    private fun resumePlayer(){
        play()
    }

    }```

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在ExoplayService的顶部显示脱机消息的文本视图怎么样？您能告诉我如何使用上面的代码吗？我想首先我需要捕获错误并使用alertdialogue显示它。在ExoplayService的顶部显示脱机消息的文本视图如何？您能告诉我如何处理上面的代码吗？我想首先我需要捕捉错误并使用alertdialogue显示它。