Android Studio: TimerTask

Question

I am creating a simple click game that spawns enemies on screen and when the user clicks them, they get points and the enemies are destroyed. I do this with making imageboxs visible and invisible when the user clicks on them. They run on a timer and have a constant loop of spawning.

Currently I want to implement a way the user will start to loose health. So I would like to check if the enemy imagebox is visible, if it is, the player will slowly loose health.

I am confused with creating a timer task that can refresh the UI for this job. I want to be able to check the UI constantly if some images are visible or not. I have made a start on this from my own research but the game crashes when loaded if this is implemented.

Timer to refresh UI:

private Timer mTimer1;
private TimerTask mTt1;
private Handler mTimerHandler = new Handler();

  public void onStart() {
    mTimer1 = new Timer();
    mTt1 = new TimerTask() {
        public void run() {
            mTimerHandler.post(new Runnable() {
                public void run() {
                    //TODO
                    final TextView health = (TextView) findViewById(R.id.Health);
                    health.setText("Health:  " + health2);

                    //Enemy ImageViews
                    final ImageView enemy1 = (ImageView) findViewById(R.id.enemy1);
                    final ImageView enemy2 = (ImageView) findViewById(R.id.enemy2);
                    final ImageView enemy3 = (ImageView) findViewById(R.id.enemy3);
                    final ImageView enemy4 = (ImageView) findViewById(R.id.enemy4);

                    //sets imageViews into array
                    final ImageView[] enemies = new ImageView[4];
                    enemies[0] = enemy1;
                    enemies[1] = enemy2;
                    enemies[2] = enemy3;
                    enemies[3] = enemy4;

                    boolean running = true;
                    while (running) {
                        if (enemy1.getVisibility() == View.VISIBLE) {
                            int damage = 1;
                            health2 = health2 - damage;
                            health.setText("Health:" + health2);
                        } else {
                            // Either gone or invisible
                        }
                        if (enemy2.getVisibility() == View.VISIBLE) {
                            int damage = 1;
                            health2 = health2 - damage;
                            health.setText("Health:" + health2);
                        } else {
                            // Either gone or invisible
                        }
                        if (enemy3.getVisibility() == View.VISIBLE) {
                            int damage = 1;
                            health2 = health2 - damage;
                            health.setText("Health:" + health2);
                        } else {
                            // Either gone or invisible
                        }
                        if (enemy4.getVisibility() == View.VISIBLE) {
                            int damage = 1;
                            health2 = health2 - damage;
                            health.setText("Health:" + health2);
                        } else {
                            // Either gone or invisible
                        }

                    }
                }
            });
        }


    };
    mTimer1.schedule(mTt1, 1, 5000);
}

}

This is the timer task I have created. I would like some clarity to why this crashes my game and how to fix this issue. I have never used timer in this way before so if the problem is obvious that is why I have not noticed it.

I have a lot more code inside the onCreate method and can post if needed. Thank you for all the help and advice for this begineer.

Crash:

Answer 1

Based on the error message you need to call super.onStart() so you need to add that here:

public void onStart() {

super.onStart();

//your code

}

I assume you know, but just in case super is class you extend, the parent. if you override it's onStart function the normal onStart procedure isn't done, if you don't call the super function.

EDIT: as for your other question, i (as a beginner with java, so i'm not claiming this is the best way to go) would be thinking along the lines of doing something like:

First create a handler and make runnables for the enemies:

Handler handler = new Handler();
Runnable[] eRunnables = new Runnable[enemies.length-1];

for(int i = 0; i < eRunnables.length; i++){
   eRunnables[i] = new Runnable(){
        public void run(){
            if(enemies[i].getVisibility() == View.VISIBLE){
                health2--;
                health.setText("Health:" + health2);
                handler.postDelayed(eRunnables[i], 1000);
            }    
        }
    };
}

And then where you initially make the enemies visible (besides setting them to visible) do something like

handler.postDelayed(eRunnable[enemyNr], 1000);

ofcourse replace the 1000 with however many milliseconds you want.

Again i'm not saying this is the best way, just what i thought up.