How to spawn enemies periodically

Question

I am attempting to create a game where enemies will spawn randomly and move towards a point on the screen. My problem is that the program waits for them to spawn and them starts moving them. I want them to start moving as they spawn and have a short break in between each one.

Here's the two main methods behind making them move:

public void newLevel() {
    runOnUiThread(new Runnable(){
        public void run() {
            int i = 0;
            while( i < 10){
                addSpeks();
                i++;
                try {
                    Thread.sleep(2000);
                }
                catch(InterruptedException ie){
                    ie.printStackTrace();
                }
            }
        }
    });
}

public void addSpeks() {
    Spek newSpek = new Spek(this);

    setRandomRegion();

    newSpek.setX(spawnX);
    newSpek.setY(spawnY);

    relativeLayout.addView(newSpek);
    spekList.add(newSpek);
    newSpek.setOnClickListener(spekListener);
    newSpek.animate().x(finalX).y(finalY).setDuration(8000);
}

Spek is a simple class which extends an ImageView and setRandomRegion() selects a random x, y coordinate on the border of the screen. I have a counter in the while loop for simplicity purposes but I would like to eventually move it to a conditional infinite loop where it only stops if you lose the game.

Thanks for any help and let me know if the problem needs more clarification.

Squeazer · Accepted Answer · 2014-11-11T13:35:38.167

1

You would have to re-run your thread when it finished, in Android it can be done like this:

First, create your Runnable:

private Runnable SpawnEnemies = new Runnable(){
    public void run(){
        //Your code here...

        spawnHandler.postDelayed(2000, this);
    }
};

Then, create a handler, which will be the class that runs the thread (or, well, runnable) and start your Runnable like this:

Handler spawnHandler = new Handler();
spawnHandler.post(new SpawnEnemies());

This will run every 2 seconds, you could also add a boolean or something simmilar to stop the loop manually.

edited Nov 11 '14 at 13:35

answered Nov 11 '14 at 08:56

Squeazer

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Not a problem, one little modification to the code, when first running `SpawnEnemies` you dont need `postDelayed(new SpawnEnemies(), 0)`, you can just do `post(new SpawnEnemies())` – Squeazer Nov 11 '14 at 13:37

Blackbelt · Answer 2 · 2014-11-11T12:14:40.770

your newLevel() method runs completely on the UI Thread, and Thread.sleep(2000); is making wait your UI Thread 2seconds each iteration. To add this sort of delay you can use an Handler:

Declare the Handler as member class

final Handler mHandler = new Handler();
int i = 0;

and change newLevel accordingly:

public void newLevel() {
    mHandler.postDelayed(new Runnable(){
        public void run() {
            if (i > 10) {
              mHandler.removeCallbacks(this);
              return;
            }
             addSpeks();
             i++;
             mHandler.postDelayed(this, 2000);                 
        }
    }), 2000);
}

Another optmization would be to declare the Runnable instance as final member, in order to avoid its instationation every time newLevel is called. Check for typo

Tried this way, but it only spawns one enemy. Also added a while loop but still only one enemy spawned. — Filipe, Nov 11 '14 at 12:13

How to spawn enemies periodically

2 Answers2