@RequiresApi(Build.VERSION_CODES.M)
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    val component = ComponentName(this, MediaService::class.java)
    mMediaBrowser = MediaBrowser(this, component, connectionCallback, null);
    mMediaBrowser.connect()
}

@RequiresApi(Build.VERSION_CODES.M)
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    val component = ComponentName(this, MediaService::class.java)
    mMediaBrowser = MediaBrowser(this, component, connectionCallback, null);
    mMediaBrowser.connect()
}
private val connectionCallback = object : MediaBrowser.ConnectionCallback() {
    override fun onConnected() {
        super.onConnected()
        ...  //連接成功后我們才可以創(chuàng)建媒體控制器
    }
    override fun onConnectionFailed() {
        super.onConnectionFailed()
    }
    override fun onConnectionSuspended() {
        super.onConnectionSuspended()
    }
}

private val connectionCallback = object : MediaBrowser.ConnectionCallback() {
    override fun onConnected() {
        super.onConnected()
         ... //返回執(zhí)行結(jié)果
        if(mMediaBrowser.isConnected) {
            val mediaId = mMediaBrowser.root
            mMediaBrowser.getItem(mediaId, itemCallback)
        }
    }
}
@RequiresApi(Build.VERSION_CODES.M)
private val itemCallback = object : MediaBrowser.ItemCallback(){
    override fun onItemLoaded(item: MediaBrowser.MediaItem?) {
        super.onItemLoaded(item)
    }
    override fun onError(mediaId: String) {
        super.onError(mediaId)
    }
}

private val connectionCallback = object : MediaBrowser.ConnectionCallback() {
    override fun onConnected() {
        super.onConnected()
        // ...
        if(mMediaBrowser.isConnected) {
            val mediaId = mMediaBrowser.root
            //需要先取消訂閱
            mMediaBrowser.unsubscribe(mediaId)
            //服務(wù)端會(huì)調(diào)用 onLoadChildren
            mMediaBrowser.subscribe(mediaId, subscribeCallback)
        }
    }
}
private val subscribeCallback = object : MediaBrowser.SubscriptionCallback(){
    override fun onChildrenLoaded(
        parentId: String,
        children: MutableList<MediaBrowser.MediaItem>
    ) {
        super.onChildrenLoaded(parentId, children)
    }
    override fun onChildrenLoaded(
        parentId: String,
        children: MutableList<MediaBrowser.MediaItem>,
        options: Bundle
    ) {
        super.onChildrenLoaded(parentId, children, options)
    }
    override fun onError(parentId: String) {
        super.onError(parentId)
    }
    override fun onError(parentId: String, options: Bundle) {
        super.onError(parentId, options)
    }
}

private val connectionCallback = object : MediaBrowser.ConnectionCallback() {
    override fun onConnected() {
        super.onConnected()
        // ...
        if(mMediaBrowser.isConnected) {
            val sessionToken = mMediaBrowser.sessionToken
            mMediaController = MediaController(applicationContext,sessionToken)
        }
    }
}

private val connectionCallback = object : MediaBrowser.ConnectionCallback() {
    override fun onConnected() {
        super.onConnected()
        // ...
        if(mMediaBrowser.isConnected) {
            val sessionToken = mMediaBrowser.sessionToken
            mMediaController = MediaController(applicationContext,sessionToken)
            mMediaController.registerCallback(controllerCallback)
        }
    }
}
private val controllerCallback = object : MediaController.Callback() {
     override fun onAudioInfoChanged(info: MediaController.PlaybackInfo?) {
        super.onAudioInfoChanged(info)
       ... //回調(diào)方法接收受控端的狀態(tài)，從而根據(jù)相應(yīng)的狀態(tài)刷新界面 UI
    }
    override fun onExtrasChanged(extras: Bundle?) {
        super.onExtrasChanged(extras)
    }
    // ...
}

private val connectionCallback = object : MediaBrowser.ConnectionCallback() {
    override fun onConnected() {
        super.onConnected()
        // ...
        if(mMediaBrowser.isConnected) {
            val sessionToken = mMediaBrowser.sessionToken
            mMediaController = MediaController(applicationContext,sessionToken)
            // 播放媒體
            mMediaController.transportControls.play()
            // 暫停媒體
            mMediaController.transportControls.pause()
        }
    }
}

const val FOLDERS_ID = "__FOLDERS__"
const val ARTISTS_ID = "__ARTISTS__"
const val ALBUMS_ID = "__ALBUMS__"
const val GENRES_ID = "__GENRES__"
const val ROOT_ID = "__ROOT__"
class MediaService : MediaBrowserService() {
    override fun onGetRoot(
        clientPackageName: String,
        clientUid: Int,
        rootHints: Bundle?
    ): BrowserRoot? {
        // 由 MediaBrowser.connect 觸發(fā)，可以通過(guò)返回 null 拒絕客戶(hù)端的連接。
        return BrowserRoot(ROOT_ID, null)
    }
    override fun onLoadChildren(
        parentId: String,
        result: Result<MutableList<MediaBrowser.MediaItem>>
    ) {
       //由 MediaBrowser.subscribe 觸發(fā)
        when (parentId) {
            ROOT_ID -> {
                // 查詢(xún)本地媒體庫(kù)
                result.detach()
                result.sendResult()
            }
            FOLDERS_ID -> {
            }
            ALBUMS_ID -> {
            }
            ARTISTS_ID -> {
            }
            GENRES_ID -> {
            }
            else -> {
            }
        }
    }
}

<service
    android:name=".MediaService"
    android:label="@string/service_name">
    <intent-filter>
        <action android:name="android.media.browse.MediaBrowserService" />
    </intent-filter>
</service>

MediaBrowserService.BrowserRoot(String rootId, Bundle extras)

const val FOLDERS_ID = "__FOLDERS__"
const val ARTISTS_ID = "__ARTISTS__"
const val ALBUMS_ID = "__ALBUMS__"
const val GENRES_ID = "__GENRES__"
const val ROOT_ID = "__ROOT__"
class MediaService : MediaBrowserService() {
    private lateinit var mediaSession: MediaSession;
    override fun onCreate() {
        super.onCreate()
        mediaSession = MediaSession(this, "TAG")
        mediaSession.setCallback(callback)
        sessionToken = mediaSession.sessionToken
    }
    // 與 MediaController.transportControls 中的大部分方法都是一一對(duì)應(yīng)的
    // 在該方法中實(shí)現(xiàn)對(duì) 播放器 的控制，
    private val callback = object : MediaSession.Callback() {
        override fun onPlay() {
            super.onPlay()
            // 處理 播放器 的播放邏輯。
            // 車(chē)載應(yīng)用的話(huà)，別忘了處理音頻焦點(diǎn)
        }
        override fun onPause() {
            super.onPause()
        }
    }
        override fun onGetRoot(
        clientPackageName: String,
        clientUid: Int,
        rootHints: Bundle?
    ): BrowserRoot? {
        Log.e("TAG", "onGetRoot: $rootHints")
        return BrowserRoot(ROOT_ID, null)
    }
    override fun onLoadChildren(
        parentId: String,
        result: Result<MutableList<MediaBrowser.MediaItem>>
    ) {
        result.detach()
        when (parentId) {
            ROOT_ID -> {
                result.sendResult(null)
            }
            FOLDERS_ID -> {
            }
            ALBUMS_ID -> {
            }
            ARTISTS_ID -> {
            }
            GENRES_ID -> {
            }
            else -> {
            }
        }
    }
    override fun onLoadItem(itemId: String?, result: Result<MediaBrowser.MediaItem>?) {
        super.onLoadItem(itemId, result)
        Log.e("TAG", "onLoadItem: $itemId")
    }
}

private val callback = object : MediaSession.Callback() {
     override fun onPlay() {
        super.onPlay()       
        if (!mediaSession.isActive) {
            mediaSession.isActive = true
        }
        //更新播放狀態(tài).
        val state = PlaybackState.Builder()
            .setState(
                PlaybackState.STATE_PLAYING,1,1f
            )
            .build()
        mediaSession.setPlaybackState(state)
    }
    override fun onPause() {
        super.onPause()
    }
    override fun onStop() {
        super.onStop()
    }
}

private val callback = object : MediaSession.Callback() {
    override fun onPlay() {
        super.onPlay()
        // 更新?tīng)顟B(tài)
        val state = PlaybackState.Builder()
            .setState(
                PlaybackState.STATE_PLAYING,1,1f
            )
            .build()
        mediaSession.setPlaybackState(state)
    }
}

PlaybackState state = new PlaybackState.Builder()
        .setState(PlaybackState.STATE_PLAYING,
                mMediaPlayer.getCurrentPosition(), PLAYBACK_SPEED)
        .setActions(PLAYING_ACTIONS)
        .addCustomAction(mShuffle)
        .setActiveQueueItemId(mQueue.get(mCurrentQueueIdx).getQueueId())
        .build();

CustomAction action = new CustomAction
        .Builder("android.car.media.localmediaplayer.shuffle",
        mContext.getString(R.string.shuffle),
        R.drawable.shuffle)
        .build();
PlaybackState state = new PlaybackState.Builder()
        .setState(PlaybackState.STATE_PLAYING,
                mMediaPlayer.getCurrentPosition(), PLAYBACK_SPEED)
        .setActions(PLAYING_ACTIONS)
        .addCustomAction(action)
        .setActiveQueueItemId(mQueue.get(mCurrentQueueIdx).getQueueId())
        .build();

class MainActivity : AppCompatActivity() {
    private lateinit var mMediaBrowser: MediaBrowser
    private lateinit var mMediaController: MediaController
    @RequiresApi(Build.VERSION_CODES.M)
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val component = ComponentName(this, MediaService::class.java)
        mMediaBrowser = MediaBrowser(this, component, connectionCallback, null);
        // 連接到 MediaBrowserService，會(huì)觸發(fā) MediaBrowserService 的 onGetRoot 方法。
        mMediaBrowser.connect()
        findViewById<Button>(R.id.btn_play).setOnClickListener {
            mMediaController.transportControls.play()
        }
    }
    private val connectionCallback = object : MediaBrowser.ConnectionCallback() {
        override fun onConnected() {
            super.onConnected()
            if (mMediaBrowser.isConnected) {
                val sessionToken = mMediaBrowser.sessionToken
                mMediaController = MediaController(applicationContext, sessionToken)
                mMediaController.registerCallback(controllerCallback)
                // 獲取根 mediaId
                val rootMediaId = mMediaBrowser.root
                // 獲取根 mediaId 的 item 列表，會(huì)觸發(fā) MediaBrowserService.onLoadItem 方法
                mMediaBrowser.getItem(rootMediaId,itemCallback)
                mMediaBrowser.unsubscribe(rootMediaId)
                // 訂閱服務(wù)端 media item 的改變，會(huì)觸發(fā) MediaBrowserService.onLoadChildren 方法
                mMediaBrowser.subscribe(rootMediaId, subscribeCallback)
            }
        }
    }
    private val controllerCallback = object : MediaController.Callback() {
        override fun onPlaybackStateChanged(state: PlaybackState?) {
            super.onPlaybackStateChanged(state)
            Log.d("TAG", "onPlaybackStateChanged: $state")
            when(state?.state){
                PlaybackState.STATE_PLAYING ->{
                    // 處理 UI
                }
                PlaybackState.STATE_PAUSED ->{
                    // 處理 UI
                }
                // 還有其它狀態(tài)需要處理
            }
        }
        //音頻信息，音量
        override fun onAudioInfoChanged(info: MediaController.PlaybackInfo?) {
            super.onAudioInfoChanged(info)
            val currentVolume = info?.currentVolume
            // 顯示在 UI 上
        }
        override fun onMetadataChanged(metadata: MediaMetadata?) {
            super.onMetadataChanged(metadata)
            val artUri = metadata?.getString(MediaMetadata.METADATA_KEY_ALBUM_ART_URI)
            // 顯示 UI 上
        }
        override fun onSessionEvent(event: String, extras: Bundle?) {
            super.onSessionEvent(event, extras)
            Log.d("TAG", "onSessionEvent: $event")
        }
        // ...
    }
    private val subscribeCallback = object : MediaBrowser.SubscriptionCallback() {
        override fun onChildrenLoaded(
            parentId: String,
            children: MutableList<MediaBrowser.MediaItem>
        ) {
            super.onChildrenLoaded(parentId, children)
        }
        override fun onChildrenLoaded(
            parentId: String,
            children: MutableList<MediaBrowser.MediaItem>,
            options: Bundle
        ) {
            super.onChildrenLoaded(parentId, children, options)
        }
        override fun onError(parentId: String) {
            super.onError(parentId)
        }
    }
    private val itemCallback = object : MediaBrowser.ItemCallback() {
        override fun onItemLoaded(item: MediaBrowser.MediaItem?) {
            super.onItemLoaded(item)
        }
        override fun onError(mediaId: String) {
            super.onError(mediaId)
        }
    }
}

const val FOLDERS_ID = "__FOLDERS__"
const val ARTISTS_ID = "__ARTISTS__"
const val ALBUMS_ID = "__ALBUMS__"
const val GENRES_ID = "__GENRES__"
const val ROOT_ID = "__ROOT__"
class MediaService : MediaBrowserService() {
    // 控制是否允許客戶(hù)端連接，并返回 root media id 給客戶(hù)端
    override fun onGetRoot(
        clientPackageName: String,
        clientUid: Int,
        rootHints: Bundle?
    ): BrowserRoot? {
        Log.e("TAG", "onGetRoot: $rootHints")
        return BrowserRoot(ROOT_ID, null)
    }
    // 處理客戶(hù)端的訂閱信息
    override fun onLoadChildren(
        parentId: String,
        result: Result<MutableList<MediaBrowser.MediaItem>>
    ) {
        Log.e("TAG", "onLoadChildren: $parentId")
        result.detach()
        when (parentId) {
            ROOT_ID -> {
                result.sendResult(null)
            }
            FOLDERS_ID -> {
            }
            ALBUMS_ID -> {
            }
            ARTISTS_ID -> {
            }
            GENRES_ID -> {
            }
            else -> {
            }
        }
    }
    override fun onLoadItem(itemId: String?, result: Result<MediaBrowser.MediaItem>?) {
        super.onLoadItem(itemId, result)
        Log.e("TAG", "onLoadItem: $itemId")
        // 根據(jù) itemId，返回對(duì)用 MediaItem
        result?.detach()
        result?.sendResult(null)
    }
    private lateinit var mediaSession: MediaSession;
    override fun onCreate() {
        super.onCreate()
        mediaSession = MediaSession(this, "TAG")
        mediaSession.setCallback(callback)
        // 設(shè)置 token
        sessionToken = mediaSession.sessionToken
    }
    // 與 MediaController.transportControls 中的方法是一一對(duì)應(yīng)的。
    // 在該方法中實(shí)現(xiàn)對(duì) 播放器 的控制，
    private val callback = object : MediaSession.Callback() {
        override fun onPlay() {
            super.onPlay()
            // 處理 播放器 的播放邏輯。
            // 車(chē)載應(yīng)用的話(huà)，別忘了處理音頻焦點(diǎn)
            Log.e("TAG", "onPlay:")
            if (!mediaSession.isActive) {
                mediaSession.isActive = true
            }
            // 更新?tīng)顟B(tài)
            val state = PlaybackState.Builder()
                .setState(
                    PlaybackState.STATE_PLAYING, 1, 1f
                )
                .build()
            mediaSession.setPlaybackState(state)
        }
        override fun onPause() {
            super.onPause()
        }
        override fun onStop() {
            super.onStop()
        }
        //省略其他方法
    }
}