构建媒体浏览器服务

private const val MY_MEDIA_ROOT_ID = "media_root_id"
private const val MY_EMPTY_MEDIA_ROOT_ID = "empty_root_id"

class MediaPlaybackService : MediaBrowserServiceCompat() {

    private var mediaSession: MediaSessionCompat? = null
    private lateinit var stateBuilder: PlaybackStateCompat.Builder

    override fun onCreate() {
        super.onCreate()

        // Create a MediaSessionCompat
        mediaSession = MediaSessionCompat(baseContext, LOG_TAG).apply {

            // Enable callbacks from MediaButtons and TransportControls
            setFlags(MediaSessionCompat.FLAG_HANDLES_MEDIA_BUTTONS
                    or MediaSessionCompat.FLAG_HANDLES_TRANSPORT_CONTROLS
            )

            // Set an initial PlaybackState with ACTION_PLAY, so media buttons can start the player
            stateBuilder = PlaybackStateCompat.Builder()
                    .setActions(PlaybackStateCompat.ACTION_PLAY
                                    or PlaybackStateCompat.ACTION_PLAY_PAUSE
                    )
            setPlaybackState(stateBuilder.build())

            // MySessionCallback() has methods that handle callbacks from a media controller
            setCallback(MySessionCallback())

            // Set the session's token so that client activities can communicate with it.
            setSessionToken(sessionToken)
        }
    }
}

public class MediaPlaybackService extends MediaBrowserServiceCompat {
    private static final String MY_MEDIA_ROOT_ID = "media_root_id";
    private static final String MY_EMPTY_MEDIA_ROOT_ID = "empty_root_id";

    private MediaSessionCompat mediaSession;
    private PlaybackStateCompat.Builder stateBuilder;

    @Override
    public void onCreate() {
        super.onCreate();

        // Create a MediaSessionCompat
        mediaSession = new MediaSessionCompat(context, LOG_TAG);

        // Enable callbacks from MediaButtons and TransportControls
        mediaSession.setFlags(
              MediaSessionCompat.FLAG_HANDLES_MEDIA_BUTTONS |
              MediaSessionCompat.FLAG_HANDLES_TRANSPORT_CONTROLS);

        // Set an initial PlaybackState with ACTION_PLAY, so media buttons can start the player
        stateBuilder = new PlaybackStateCompat.Builder()
                            .setActions(
                                PlaybackStateCompat.ACTION_PLAY |
                                PlaybackStateCompat.ACTION_PLAY_PAUSE);
        mediaSession.setPlaybackState(stateBuilder.build());

        // MySessionCallback() has methods that handle callbacks from a media controller
        mediaSession.setCallback(new MySessionCallback());

        // Set the session's token so that client activities can communicate with it.
        setSessionToken(mediaSession.getSessionToken());
    }
}

override fun onGetRoot(
        clientPackageName: String,
        clientUid: Int,
        rootHints: Bundle?
): MediaBrowserServiceCompat.BrowserRoot {

    // (Optional) Control the level of access for the specified package name.
    // You'll need to write your own logic to do this.
    return if (allowBrowsing(clientPackageName, clientUid)) {
        // Returns a root ID that clients can use with onLoadChildren() to retrieve
        // the content hierarchy.
        MediaBrowserServiceCompat.BrowserRoot(MY_MEDIA_ROOT_ID, null)
    } else {
        // Clients can connect, but this BrowserRoot is an empty hierarchy
        // so onLoadChildren returns nothing. This disables the ability to browse for content.
        MediaBrowserServiceCompat.BrowserRoot(MY_EMPTY_MEDIA_ROOT_ID, null)
    }
}

@Override
public BrowserRoot onGetRoot(String clientPackageName, int clientUid,
    Bundle rootHints) {

    // (Optional) Control the level of access for the specified package name.
    // You'll need to write your own logic to do this.
    if (allowBrowsing(clientPackageName, clientUid)) {
        // Returns a root ID that clients can use with onLoadChildren() to retrieve
        // the content hierarchy.
        return new BrowserRoot(MY_MEDIA_ROOT_ID, null);
    } else {
        // Clients can connect, but this BrowserRoot is an empty hierarchy
        // so onLoadChildren returns nothing. This disables the ability to browse for content.
        return new BrowserRoot(MY_EMPTY_MEDIA_ROOT_ID, null);
    }
}

override fun onLoadChildren(
        parentMediaId: String,
        result: MediaBrowserServiceCompat.Result<List<MediaBrowserCompat.MediaItem>>
) {
    //  Browsing not allowed
    if (MY_EMPTY_MEDIA_ROOT_ID == parentMediaId) {
        result.sendResult(null)
        return
    }

    // Assume for example that the music catalog is already loaded/cached.

    val mediaItems = emptyList<MediaBrowserCompat.MediaItem>()

    // Check if this is the root menu:
    if (MY_MEDIA_ROOT_ID == parentMediaId) {
        // Build the MediaItem objects for the top level,
        // and put them in the mediaItems list...
    } else {
        // Examine the passed parentMediaId to see which submenu we're at,
        // and put the children of that menu in the mediaItems list...
    }
    result.sendResult(mediaItems)
}

@Override
public void onLoadChildren(final String parentMediaId,
    final Result<List<MediaItem>> result) {

    //  Browsing not allowed
    if (TextUtils.equals(MY_EMPTY_MEDIA_ROOT_ID, parentMediaId)) {
        result.sendResult(null);
        return;
    }

    // Assume for example that the music catalog is already loaded/cached.

    List<MediaItem> mediaItems = new ArrayList<>();

    // Check if this is the root menu:
    if (MY_MEDIA_ROOT_ID.equals(parentMediaId)) {
        // Build the MediaItem objects for the top level,
        // and put them in the mediaItems list...
    } else {
        // Examine the passed parentMediaId to see which submenu we're at,
        // and put the children of that menu in the mediaItems list...
    }
    result.sendResult(mediaItems);
}

// Given a media session and its context (usually the component containing the session)
// Create a NotificationCompat.Builder

// Get the session's metadata
val controller = mediaSession.controller
val mediaMetadata = controller.metadata
val description = mediaMetadata.description

val builder = NotificationCompat.Builder(context, channelId).apply {
    // Add the metadata for the currently playing track
    setContentTitle(description.title)
    setContentText(description.subtitle)
    setSubText(description.description)
    setLargeIcon(description.iconBitmap)

    // Enable launching the player by clicking the notification
    setContentIntent(controller.sessionActivity)

    // Stop the service when the notification is swiped away
    setDeleteIntent(
            MediaButtonReceiver.buildMediaButtonPendingIntent(
                    context,
                    PlaybackStateCompat.ACTION_STOP
            )
    )

    // Make the transport controls visible on the lockscreen
    setVisibility(NotificationCompat.VISIBILITY_PUBLIC)

    // Add an app icon and set its accent color
    // Be careful about the color
    setSmallIcon(R.drawable.notification_icon)
    color = ContextCompat.getColor(context, R.color.primaryDark)

    // Add a pause button
    addAction(
            NotificationCompat.Action(
                    R.drawable.pause,
                    getString(R.string.pause),
                    MediaButtonReceiver.buildMediaButtonPendingIntent(
                            context,
                            PlaybackStateCompat.ACTION_PLAY_PAUSE
                    )
            )
    )

    // Take advantage of MediaStyle features
    setStyle(android.support.v4.media.app.NotificationCompat.MediaStyle()
            .setMediaSession(mediaSession.sessionToken)
            .setShowActionsInCompactView(0)

            // Add a cancel button
            .setShowCancelButton(true)
            .setCancelButtonIntent(
                    MediaButtonReceiver.buildMediaButtonPendingIntent(
                            context,
                            PlaybackStateCompat.ACTION_STOP
                    )
            )
    )
}

// Display the notification and place the service in the foreground
startForeground(id, builder.build())

// Given a media session and its context (usually the component containing the session)
// Create a NotificationCompat.Builder

// Get the session's metadata
MediaControllerCompat controller = mediaSession.getController();
MediaMetadataCompat mediaMetadata = controller.getMetadata();
MediaDescriptionCompat description = mediaMetadata.getDescription();

NotificationCompat.Builder builder = new NotificationCompat.Builder(context, channelId);

builder
    // Add the metadata for the currently playing track
    .setContentTitle(description.getTitle())
    .setContentText(description.getSubtitle())
    .setSubText(description.getDescription())
    .setLargeIcon(description.getIconBitmap())

    // Enable launching the player by clicking the notification
    .setContentIntent(controller.getSessionActivity())

    // Stop the service when the notification is swiped away
    .setDeleteIntent(MediaButtonReceiver.buildMediaButtonPendingIntent(context,
       PlaybackStateCompat.ACTION_STOP))

    // Make the transport controls visible on the lockscreen
    .setVisibility(NotificationCompat.VISIBILITY_PUBLIC)

    // Add an app icon and set its accent color
    // Be careful about the color
    .setSmallIcon(R.drawable.notification_icon)
    .setColor(ContextCompat.getColor(context, R.color.primaryDark))

    // Add a pause button
    .addAction(new NotificationCompat.Action(
        R.drawable.pause, getString(R.string.pause),
        MediaButtonReceiver.buildMediaButtonPendingIntent(context,
            PlaybackStateCompat.ACTION_PLAY_PAUSE)))

    // Take advantage of MediaStyle features
    .setStyle(new MediaStyle()
        .setMediaSession(mediaSession.getSessionToken())
        .setShowActionsInCompactView(0)

        // Add a cancel button
       .setShowCancelButton(true)
       .setCancelButtonIntent(MediaButtonReceiver.buildMediaButtonPendingIntent(context,
           PlaybackStateCompat.ACTION_STOP)));

// Display the notification and place the service in the foreground
startForeground(id, builder.build());