Prepare Unity without showing UnityPlayer

I'm integrating Unity as a subview in a native Android app.

I'd need to prepare Unity when the app starts, but without showing it, because I need to change between scenes when the user taps a button, without showing the Unity screen presentation. Also if I try to send a message without making sure that the UnityPlayer is ready, it doesn't process the message.

The flow is:

User chooses a scene -> Display scene in a different activity with UnityPlayer.UnitySendMessage

In iOS I did it like this:

 class AppDelegate: UIResponder, UIApplicationDelegate {

 var window: UIWindow?

 var currentUnityController: UnityAppController!


 func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
     self.currentUnityController = UnityAppController()

     self.currentUnityController.application(application, didFinishLaunchingWithOptions: launchOptions)

     return true
 }

 

But I don't find something similar in Android. This is how I'm showing the UnityPlayer in a subview:

 public class PlayGameActivity extends UnityPlayerActivity {
     private static final String TAG = "PlayGameActivity";
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_play_game);
 
         // Create the UnityPlayer
         mUnityPlayer = new UnityPlayer(this);
         int glesMode = mUnityPlayer.getSettings().getInt("gles_mode", 1);
         boolean trueColor8888 = false;
         mUnityPlayer.init(glesMode, trueColor8888);
 
         // Add the Unity view
         RelativeLayout layout = (RelativeLayout) findViewById(R.id.container_unity_play_game_activity);
         RelativeLayout.LayoutParams lp = (RelativeLayout.LayoutParams) layout.getLayoutParams();
         layout.addView(mUnityPlayer.getView(), 0, lp);
 
         String unityScene = "some_scene";
         Log.d(TAG, "calling scene " + unityScene);
         UnityPlayer.UnitySendMessage("AController", "AMethodToChangeScene", unityScene);
     }
 }

I tried changing scene in an Activity with the player and the buttons below, and it works, because I wait for the player to be ready.

So is there a way to init Unity without showing it like in iOS? Or a way to know when the UnityPlayer is ready to receive messages?