How can I detect if two images from different NSMutableArrays collide?

[Kenenth]

I'm having a bit of difficultys with detecting collision from two seperate NSMutableArrays. I have figured out that you cant just nest a for loop inside of another, because I need to make changes(delete both of the items from each array if they collide). It works sometimes but most of the times it crashes. this is my current attempt:

		for (int objectCounter1=[object1Array count]-1; objectCounter1>= 0; objectCounter1--){
			for (int objectCounter2=[object2Array count]-1; objectCounter2>= 0; objectCounter2--){
				UIImageView *Object1 = [object1Array objectAtIndex:objectCounter1];
				UIImageView *Object2 = [object2Array objectAtIndex:objectCounter2];
				if( CGRectIntersectsRect(Object1.frame, Object2.frame)) {
					[Object1 removeFromSuperview];
					[object1Array removeObjectAtIndex:objectCounter1];
					Object 1 = nil;
					[Object2 removeFromSuperview];
					[object2Array removeObjectAtIndex:objectCounter2];
					Object2= nil;
					score = score+50;
                                        }
                         }
            }

This does not work. It crashes every few times, saying something along the lines of [NSMutableArray objectAtIndex:] index 2 beyond bounds (0....1).
This is very complicating explaining why it doesnt work, but here you go.

say if you start with 3 items in each array. item one at index 0, item 2 at index 1, and item 3 at index 2. If you loop through the array and item 2 from both arrays collide. Then they both get deleted at the index they were found. But, the for loop is still going, and It still thinks there is an Index where both of the items were deleted, so it tries to run the loop attempting to get objectatindex:2, even though an Item has just been deleted from each array, so that means only 2 objects left in each array(the bound being 0...1) .

is there any way I can accomplish this task without getting the crash and it working fully functional? Thanks a million in advance.

[smithdale87]

It's a big NO NO to try and remove objects from an array while you are iterating over it. This is causing your index out of bounds problems.

A better approach would be to create two temporary arrays. When you detect a collision, then add the objects to their respective temp array (object1 goes into object1 temp array, object2 goes into object 2 temp array). AFTER youf nested for loops, you can then iterate over each of the items in those arrays and do something like this:

for( UIImageView* obj1 in tempArray1 )
{
   [obj1 removeFromSuperview];
   [object1Array removeObject: obj1];
    score+=50;
}

//do the same thing for tempArray2 and remove those objects from object2Array

[smasher]

Iterating over the array backwards is fine; it's my preferred way of doing this. Your only problem is the nested loops; if your object1[n] hits something in the middle of the object2 array you remove both items; *but* you keep looping the object2 array and checking it against the now-dead object1[n]. You need to break out of the inner loop with a "break" statement. Try this:

for (int objectCounter1=[object1Array count]-1; objectCounter1>= 0; objectCounter1--){
	for (int objectCounter2=[object2Array count]-1; objectCounter2>= 0; objectCounter2--){
		UIImageView *Object1 = [object1Array objectAtIndex:objectCounter1];
		UIImageView *Object2 = [object2Array objectAtIndex:objectCounter2];
		if( CGRectIntersectsRect(Object1.frame, Object2.frame)) {
			[Object1 removeFromSuperview];
			[object1Array removeObjectAtIndex:objectCounter1];
			Object 1 = nil;
			[Object2 removeFromSuperview];
			[object2Array removeObjectAtIndex:objectCounter2];
			Object2= nil;
			score = score+50;

			//smasher change
			break;
		}
	}
}

[Kenenth]

Thank you so much. smithdale, its a good idea, but for smashers all i have to write is "break;".This has been troubling me for about a week. Now my app is 100% working . Again Thanks!