Question

I’ve just started with Android programming using eclipse and recently came across this problem. I have a bunch of sprites assigned to an arraylist. Now, I want to make it so that collision is detected automatically between sprites but the template I’m currently using can only detect collision between the surface’s borders and the moving sprites. Each sprite’s position and speed is generated randomly.
How can I change the update() function in my Sprite() class to detect collision between the moving sprites themselves and at the same changing/bouncing to the opposite direction?
Here’s my Sprite class template:

package com.gameproject.cai_test;

import java.util.Random;


   public Sprite(GameView gameView, Bitmap bmp) {
         this.width = bmp.getWidth() / BMP_COLUMNS;
         this.height = bmp.getHeight() / BMP_ROWS;
         this.gameView = gameView;
         this.bmp = bmp;


         Random rnd = new Random();
         x = rnd.nextInt(gameView.getWidth() - width);
         y = rnd.nextInt(gameView.getHeight() - height);
         xSpeed = rnd.nextInt(MAX_SPEED * 2) - MAX_SPEED;
         ySpeed = rnd.nextInt(MAX_SPEED * 2) - MAX_SPEED;
   }

private void update() {
         if (x >= gameView.getWidth() - width - xSpeed || x + xSpeed <= 0) {
                xSpeed = -xSpeed;
         }
         x = x + xSpeed;
         if (y >= gameView.getHeight() - height - ySpeed || y + ySpeed <= 0) {
                ySpeed = -ySpeed;
         }
         y = y + ySpeed;

         currentFrame = ++currentFrame % BMP_COLUMNS;
   }

   public void onDraw(Canvas canvas) {
         update();
         int srcX = currentFrame * width;
         int srcY = getAnimationRow() * height;
         Rect src = new Rect(srcX, srcY, srcX + width, srcY + height);
         Rect dst = new Rect(x, y, x + width, y + height);

         canvas.drawBitmap(bmp, src, dst, null);
   }

   private int getAnimationRow() {
         double dirDouble = (Math.atan2(xSpeed, ySpeed) / (Math.PI / 2) + 2);
         int direction = (int) Math.round(dirDouble) % BMP_ROWS;
         return DIRECTION_TO_ANIMATION_MAP[direction];
   }


   //gameplay operations

   //only values from 0 to 9 will be picked; each assigned its own sprite in the list
   public int randomValue(){
       Random rnd = new Random();
       RandomValue = rnd.nextInt(10);
       return RandomValue; 
   }

   //sequence operation from addition, subtraction, multiplication, and division
   public int produceSum(){
       int addOne = 0;
       int addTwo = 0;
       Sum = addOne + addTwo;
       return Sum;
   }

   public int produceDiff(){
       int deductOne = 0;
       int deductTwo = 0;
       Difference = deductOne - deductTwo;
       return Difference;
   }

   public int produceProduct(){
       int multiOne = 0;
       int multiTwo = 0;
       Product = multiOne * multiTwo;
       return Product;
   }

   public int produceQuotient(){
       int divideOne = 0;
       int divideTwo = 0;
       Quotient = divideOne / divideTwo;
       return Quotient;
   }

   //each time this returns true, the game is reset with new operation
   //compares the value of the bubble picked to the random number being compared through operations
   public boolean compareBubbleValue(int randomBubble, int bubbleValue){

       if (randomBubble == bubbleValue){
           return true;
       }
       return false;
   }

}

As you can see, the update() method only checks the collision between the moving sprites and the borders.

Answer 1

Okey, so lets name your array of sprites spriteArray and loop through it twice

 public Rect getBounds(){ //put this in your sprite and enemy-class.
   return new Rect(x, y, x+width, y+height);
 }

 Public void checkCollision(){
    for (int i = 0; i<spriteArray.size(); i++){
           Rect mySprite = spriteArray.get(i).getBounds(); //create rect for every sprite in array
             for (int j = 0; j<spriteArray.size(); i++){
                Rect myOtherSprite = spriteArray.get(i).getBounds();
                  if(mySprite.intersect(myOtherSprite)){ //check if they touch
                   //Todo code here
             }
          }
      }
  }

then you just put this method in your update-method.