Fix GitHub issue #250

MusicService wasn't getting started, leading to a situation where the
service would be killed and the ExoPlayer playback thread would continue
to play queued songs until it was also killed or it completed the queue.

This change ensures the service is started when playback begins so that
the client may unbind without service being killed immediately.

Change-Id: Ib4a846c2e60d3f0644b0b5843d1815dbd3caef68

media/src/main/java/com/example/android/uamp/media/MusicService.kt

@@ -164,9 +164,22 @@ class MusicService : MediaBrowserServiceCompat() {
         packageValidator = PackageValidator(this, R.xml.allowed_media_browser_callers)
     }
 
+    /**
+     * This is the code that causes UAMP to stop playing when swiping it away from recents.
+     * The choice to do this is app specific. Some apps stop playback, while others allow playback
+     * to continue and allow uses to stop it with the notification.
+     */
     override fun onTaskRemoved(rootIntent: Intent) {
         super.onTaskRemoved(rootIntent)
-        stopSelf()
+
+        /**
+         * By stopping playback, the player will transition to [Player.STATE_IDLE]. This will
+         * cause a state change in the MediaSession, and (most importantly) call
+         * [MediaControllerCallback.onPlaybackStateChanged]. Because the playback state will
+         * be reported as [PlaybackStateCompat.STATE_NONE], the service will first remove
+         * itself as a foreground service, and will then call [stopSelf].
+         */
+        exoPlayer.stop(true)
     }
 
     override fun onDestroy() {
@@ -288,21 +301,36 @@ class MusicService : MediaBrowserServiceCompat() {
                 PlaybackStateCompat.STATE_PLAYING -> {
                     becomingNoisyReceiver.register()
 
-                    startForeground(NOW_PLAYING_NOTIFICATION, notification)
-                    isForegroundService = true
+                    /**
+                     * This may look strange, but the documentation for [Service.startForeground]
+                     * notes that "calling this method does *not* put the service in the started
+                     * state itself, even though the name sounds like it."
+                     */
+                    if (!isForegroundService) {
+                        startService(Intent(applicationContext, this@MusicService.javaClass))
+                        startForeground(NOW_PLAYING_NOTIFICATION, notification)
+                        isForegroundService = true
+                    } else if (notification != null) {
+                        notificationManager.notify(NOW_PLAYING_NOTIFICATION, notification)
+                    }
                 }
                 else -> {
                     becomingNoisyReceiver.unregister()
 
                     if (isForegroundService) {
                         stopForeground(false)
+                        isForegroundService = false
+
+                        // If playback has ended, also stop the service.
+                        if (updatedState == PlaybackStateCompat.STATE_NONE) {
+                            stopSelf()
+                        }
 
                         if (notification != null) {
                             notificationManager.notify(NOW_PLAYING_NOTIFICATION, notification)
                         } else {
                             removeNowPlayingNotification()
                         }
-                        isForegroundService = false
                     }
                 }
             }