Question

I am trying to make a onTouchEvent to create a missile that will launch from my character sprite and forward.
I have this working using

        if (missdraw = true){
            canvas.drawBitmap(missile,missilex,missileY,null);
            missilex = missilex + 14;
            missdraw = false;
        }

in my onDraw method, but the problem is it will only create one at a time.
I tried to create a class to deal with this, but this just causes an error and crashes when i try to fire.
here is what i use for the class: (this is in the ondraw in my gameview)

        for (Batcher missile : missiles ){
            missile.onDraw(canvas);
        }

this is in the class

public Batcher(List<Batcher> temps, ScreenActivity newView, float x,
        float y, Bitmap missile){

    this.x = 1;
    this.y = 2;
    this.missile = missile;

}

public void onDraw(Canvas canvas) {
    // TODO Auto-generated method stub
    canvas.drawBitmap(missile, x,y, null);

}

I would appreciate any help, but also if you could explain how it would work, instead of just code, as im quite new to programming, and really need to understand what im doing and why im doing it, rather than just copying peoples code because it works.

Cheers Phil.

Answer 1

Your concepts are pretty good, actually. There are a few things I don’t quite understand about the code samples you posted up, I’ll try to translate into what I’d do and you can tell me if I’m doing it wrong 🙂

in your game class you need (and it looks like you have) a list of Missiles:

LinkedList<Batcher> missiles;

In your onTouch(), however a missile is created –

missiles.add(new Batcher(missilex, missiley, missile));

you now have a collection of missiles. Note that I didn’t include the list in the constructor of your batcher, because an object should never need to know that it’s a part of a collection. All it needs to know is how to draw itself and where. Since I assume that all of your missiles will be added to or removed from the screen frequently, while only having a few on screen at a time, I’ve used a LinkedList, which is fast for adding and removing, but slow for accessing a specific missile. If you needed to access specific items in the collection and the collection didn’t change very much, you would use an ArrayList instead. on to onDraw – as you have it the missile draws itself, which is fine, but I prefer to let the View do the drawing, with the missile telling it where it should be drawn –

for (Batcher missile : missiles ){
  missile.setX(missile.getX() + 14); // to make it move
  if (missile.getX() > canvas.gedWidth()) { //check if it's left the screen
    missiles.remove(missile); // Remove it
  }
  else { //perform drawing
    canvas.drawBitmap(missile.getBitmap(), missile.getX(), missile.getY(), null);
  }
}

Hopefully that’ll do it for you, but feel free to let me know if there’s anything you’d like me to explain more!