Question

Can someone give me an example of how a child class would access the canvas of the parent class to draw something, i.e a bitmap:

BitmapFactory.Options options = new BitmapFactory.Options();
    options.inPurgeable = true;
    Bitmap bitmap_explosion = BitmapFactory.decodeResource(context.getResources(),com.forwardapps.tanks.R.drawable.explosion, options);

context.drawBitmap(bitmap_explosion, x, y, null);

This is what I have in the child, in the parent I’ve got:

Explosion xplode = new Explosion(this._context, 50, 50);

I’ve been looking around for a few hours now, no luck.

Answer 1

You don’t draw Bitmaps randomly in code. You would need to submit your object to some type of rendering view. So for example you might have:

public class Scene extends View{
  private List<Explosions> explosions = new ArrayList<Explosions>();
  @Override
  public void onDraw(){
     //obviously i have a concurrency issue here.. meh
     for (Explosions e:explosions){
     /// draw your explosions here

     }

  }

  public void addExplosion(Explosions x){
       explosions.add(x)
  }
}

When you call add explosions, dont forget to call postInvalidate to ask the view to redraw it’s self.

But to answer your question most directly, you want your child class to implement Drawable and then pass the canvas to the child classes onDraw() method from the parent classes onDraw method.