Question

I have two objects: one that is moving by animation, and another that is moving when I drag it around with my finger. I want to be able to detect when the two “collide” using CGIntersectsRect. However, I’ve heard that in order to do this with animations, I need to access the presentation layer to grab values from there. I have no idea how to go about doing this, however. This is the animation code I have:

UIImage *flakeImage = [UIImage imageNamed:@"apple.png"];
UIImageView *flakeView = [[UIImageView alloc] initWithImage:flakeImage];
flakeView.frame = CGRectMake(200, -25.0, 25.0, 25.0);
[self.view addSubview:flakeView];

[UIView beginAnimations:nil context:(flakeView)];
[UIView setAnimationDuration:2];

flakeView.frame = CGRectMake(200, 800.0, 25.0, 25.0); ]

and here is the code for the object I move with my finger:

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    // get current touch location
    UITouch *touch = [[event touchesForView:self.view] anyObject];
    CGPoint point = [touch locationInView:self.view];
    // update location of the image
    basketView.center = CGPointMake(point.x, basketView.center.y);


}

How can I access the presentationLayer of the flakeView animation so that I can detect when the two objects intersect?

Answer 1

You simply need to keep around a reference to both of your views. Then all you have to do is:

if(CGRectIntersectsRect(((CALayer*)basketView.layer.presentationLayer).frame, 
    ((CALayer*)flakeView.layer.presentationLayer).frame)) {
    //handle the collision
}