ep-af-wrapper.kt

class AudioFocusWrapper(private val audioAttributes: AudioAttributesCompat,
                        private val audioManager: AudioManager,
                        private val player: SimpleExoPlayer) : ExoPlayer by player, AnkoLogger {
    private var shouldPlayWhenReady = false

    private val audioFocusListener =
            AudioManager.OnAudioFocusChangeListener { focusChange ->
                when (focusChange) {
                    AudioManager.AUDIOFOCUS_GAIN -> {
                        if (shouldPlayWhenReady || player.playWhenReady) {
                            player.playWhenReady = true
                            player.volume = MEDIA_VOLUME_DEFAULT
                        }
                        shouldPlayWhenReady = false
                    }
                    AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK -> {
                        if (player.playWhenReady) {
                            player.volume = MEDIA_VOLUME_DUCK
                        }
                    }
                    AudioManager.AUDIOFOCUS_LOSS_TRANSIENT -> {
                        shouldPlayWhenReady = player.playWhenReady
                        player.playWhenReady = false
                    }
                    AudioManager.AUDIOFOCUS_LOSS -> {
                        abandonAudioFocus()
                    }
                }
            }

    @get:RequiresApi(Build.VERSION_CODES.O)
    private val audioFocusRequest by lazy { buildFocusRequest() }

    override fun setPlayWhenReady(playWhenReady: Boolean) {
        if (playWhenReady) requestAudioFocus() else abandonAudioFocus()
    }

    private fun requestAudioFocus() {
        val result = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            requestAudioFocusOreo()
        } else {
            @Suppress("deprecation")
            audioManager.requestAudioFocus(audioFocusListener,
                    audioAttributes.legacyStreamType,
                    AudioManager.AUDIOFOCUS_GAIN)
        }

        // Call the listener whenever focus is granted - even the first time!
        if (result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
            shouldPlayWhenReady = true
            audioFocusListener.onAudioFocusChange(AudioManager.AUDIOFOCUS_GAIN)
        } else {
            warn { "Playback not started: Audio focus request denied" }
        }
    }

    private fun abandonAudioFocus() {
        player.playWhenReady = false
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            abandonAudioFocusOreo()
        } else {
            @Suppress("deprecation")
            audioManager.abandonAudioFocus(audioFocusListener)
        }
    }

    @RequiresApi(Build.VERSION_CODES.O)
    private fun requestAudioFocusOreo(): Int = 
        audioManager.requestAudioFocus(audioFocusRequest)

    @RequiresApi(Build.VERSION_CODES.O)
    private fun abandonAudioFocusOreo() = 
        audioManager.abandonAudioFocusRequest(audioFocusRequest)

    @TargetApi(Build.VERSION_CODES.O)
    private fun buildFocusRequest(): AudioFocusRequest =
            AudioFocusRequest.Builder(AudioManager.AUDIOFOCUS_GAIN)
                    .setAudioAttributes(
                         audioAttributes.unwrap() as? AudioAttributes)
                    .setOnAudioFocusChangeListener(audioFocusListener)
                    .build()
}

private const val MEDIA_VOLUME_DEFAULT = 1.0f
private const val MEDIA_VOLUME_DUCK = 0.2f

Finally, to use this instead of a SimpleExoPlayer here’s what the PlayerHolder class (that you’ve seen in the previous parts of this series of articles) looks like.

class PlayerHolder(val context: Context,
                   val playerState: PlayerState,
                   val playerView: PlayerView) : AnkoLogger {
    val audioFocusPlayer: ExoPlayer

    // Create the player instance.
    init {
        val audioManager = 
                context.getSystemService(Context.AUDIO_SERVICE) as AudioManager
        val audioAttributes = AudioAttributesCompat.Builder()
                .setContentType(AudioAttributesCompat.CONTENT_TYPE_MUSIC)
                .setUsage(AudioAttributesCompat.USAGE_MEDIA)
                .build()
        audioFocusPlayer = AudioFocusWrapper(
                audioAttributes,
                audioManager,
                ExoPlayerFactory.newSimpleInstance(
                    context, DefaultTrackSelector())
                        .apply { playerView.player = this }
        )
        info { "SimpleExoPlayer created" }
    }