Question

In my app I have this code in viewWillAppear. It simply animates random object from top of the screen to the bottom. The problem is I need to detect collision and what I have learnt so far is it is impossible to retrieve the coordinates at any time for an animation. so how can I implement it by using NSTimer? or shall I use NSTimer? I could not figure it out. Any clue will be appreciated.

-(void)viewWillAppear:(BOOL)animated
{
    for (int i = 0; i < 100; i++) {

        p = arc4random_uniform(320)%4+1;

        CGRect startFrame = CGRectMake(p*50, -50, 50, 50);
        CGRect endFrame   = CGRectMake(p*50, CGRectGetHeight(self.view.bounds) + 50,
                                       50,
                                       50);

        animatedView = [[UIView alloc] initWithFrame:startFrame];
        animatedView.backgroundColor = [UIColor redColor];

        [self.view addSubview:animatedView];

        [UIView animateWithDuration:2.f
                              delay:i * 0.5f
                            options:UIViewAnimationCurveLinear
                         animations:^{
                             animatedView.frame = endFrame;
                         } completion:^(BOOL finished) {
                             [animatedView removeFromSuperview];
                         }];

}

Answer 1

Your statement:

is it is impossible to retrieve the coordinates at any time for an
animation

seems incorrect did you check this?

It looks like you can use the CALayer’s presentationLayer property to extract coordinates info during an animation:

CGRect movingFrame = [[yourView.layer presentationLayer] frame];

I will use this info to check time to time if there is a collision during the animation. So I will use the timer to check the collision status not for animating the views.