Btukfyl

I am having this issue on an app that I made. It's a simple game that I loads data from Room database in my onCreate method, saves the loaded data in List<GameData> gameData and then starts the game.

gameDao.getAll()

    .subscribe(gameDatas -> {

        gameData.addAll(gameDatas);

        startGame();

    });

inside my startGame, I randomly select a number in the range [0, gameData.size()] and do some game related work with the corresponding gameData.

public void startGame(){

    Random random = new Random();

    int randomNumber = random.nextInt(gameData.size());



    // do something with gameData[ramdomNumber]

}

So, then user keeps playing and then when the user loses I send him to GameOverActivity with startActivityForResult(gameOver,1123)

Inside GameOverActivity user can

• restart the game


• watch an ad to continue playing


• other social related staff

So when the user presses restart button, I just finish the GameOverActivity which will redirect me to onActivityResult of GameActivity. Here I just call startGame method again, and it should supposedly start a new game.

Now the problem is sometimes for certain devices, gameData is getting empty and hence I am getting exception inside startGame when I call random.nextInt(gameData.size())

java.lang.RuntimeException: 



  at android.app.ActivityThread.performResumeActivity (ActivityThread.java:3790)



  at android.app.ActivityThread.handleResumeActivity (ActivityThread.java:3830)



  at android.app.ActivityThread.handleLaunchActivity (ActivityThread.java:3038)



  at android.app.ActivityThread.-wrap11 (Unknown Source)



  at android.app.ActivityThread$H.handleMessage (ActivityThread.java:1696)



  at android.os.Handler.dispatchMessage (Handler.java:105)



  at android.os.Looper.loop (Looper.java:164)



  at android.app.ActivityThread.main (ActivityThread.java:6944)



  at java.lang.reflect.Method.invoke (Native Method)



  at com.android.internal.os.Zygote$MethodAndArgsCaller.run (Zygote.java:327)



  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1374)

Caused by: java.lang.RuntimeException: 



  at android.app.ActivityThread.deliverResults (ActivityThread.java:4491)



  at android.app.ActivityThread.performResumeActivity (ActivityThread.java:3762)

Caused by: java.lang.IllegalArgumentException: 



  at java.util.Random.nextInt (Random.java:388)



  at com.company.game.GameActivity.startGame (GameActivity.java:149)



  at com.company.game.GameActivity.onActivityResult (GameActivity.java:477)



  at android.app.Activity.dispatchActivityResult (Activity.java:7556)



  at android.app.ActivityThread.deliverResults (ActivityThread.java:4487)

I am not understating why would gameData is getting cleared, and I am not able to check because I have never encountered while testing and I got the crash report from PlayConsole. Any idea what might be causing this?

I suspect the problem happens when the OS destroys the GamaActivity due to memory needs, and then recreates it for the onActivityResult. This is part of the normal Android Activity Lifecycle. Now when that happens, gameData will be null, and onCreate is called to init. onCreate will call again the Room function to fill gameData, but as Room is asynchronous, it will let onCreate finish, before the gameData is filled. At that point, onActivityResult will be called, and gameData may still empty, as the the Room code hasn't finished, so app crashes.
The correct way to fix this, is to move gameData out of the Activity class, and to the Application class. That is where it belongs, as data should be tied to the Application, not the Activity. You will have to extend the Application class, and in the onCreate of the Application, init the Room data. Just Google "Extending Android Application Class" for specific instructions. This way the data will be safe for the lifetime of the application.