UIImageView animating on UIBezierPath not detecting collision - objective-c

Question

I have a UIImageView travelling on a UIBezierPath:
- (void)viewDidLoad {
[super viewDidLoad];
UIBezierPath *path = [UIBezierPath bezierPath];
[path moveToPoint:CGPointMake(60, 60)];
[path addLineToPoint:CGPointMake(70, 70)];
[path addLineToPoint:CGPointMake(80, 120)];
[self.thingy setImage:[UIImage imageNamed:#"titles.png"]];
[self.thingy.layer setPosition:CGPointMake(60, 60)];
[self.view.layer addSublayer:self.thingy.layer];
CAKeyframeAnimation *anim = [CAKeyframeAnimation animationWithKeyPath:#"position"];
anim.path = path.CGPath;
anim.rotationMode = kCAAnimationRotateAuto;
anim.duration = 8.0;
[self.thingy.layer addAnimation:anim forKey:#"move"];
self.timer = [NSTimer scheduledTimerWithTimeInterval:1
target:self
selector:#selector(tester)
userInfo:nil
repeats:YES];
}
Goal: I want to detect whether thingy collides with a barrier. Here is tester:
- (void) tester {
NSLog(#"calling method");
if (CGRectIntersectsRect(self.thingy.frame, self.barrier.frame)) {
NSLog(#"collided");
}
}
barrier and thingy are both UIImageViews declared as weak and nonatomic in the header file.
Problem: tester is always being called every second, but when the two UIImageViews collide nothing happens. Any help to try and make this work?

Answer 1

Since thingy is being animated, you won't get accurate values from its frame. If I recall correctly, once the animation starts, the view will immediately have the final frame from the end of the animation. If you want to test thingy's frame while it is in motion, you have to test the frame of thingy's layer's presentationLayer. Something like this:
- (void) tester {
NSLog(#"calling method");
if (CGRectIntersectsRect(((CALayer *)[self.thingy.layer presentationLayer]).frame, self.barrier.frame)) {
NSLog(#"collided");
}
}
Note: If your barrier is in motion too, you'll have to use its presentationLayer as well.