Question

I would like to have an UIImageView that flickers. I thougt I can make it with CoreAnimation and the alpha-value. I tried this:

for (int a = 1; a <= 100; a++) {
    schwarz.alpha = 0.7;
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
    [UIView setAnimationDuration:1];
    schwarz.alpha = 0,1;
    [UIView commitAnimations];
}

but it doenst work. He just moves to 0.1 and not again to 0.7.
I also tried this:

schwarz.alpha = 0.7;
[UIView beginAnimations:nil context:nil];
[UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
[UIView setAnimationDuration:1];
schwarz.alpha = 0.1;
[UIView commitAnimations];
[UIView beginAnimations:nil context:nil];
[UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
[UIView setAnimationDuration:1];
schwarz.alpha = 1;
[UIView commitAnimations];
[UIView commitAnimations];
[UIView beginAnimations:nil context:nil];
[UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
[UIView setAnimationDuration:1];
schwarz.alpha = 3;
[UIView commitAnimations];
// and so on...

And again It doenst work. How can I implement the flickering?
Thanks!

Answer 1

The problem with your code is that the [UIView commitAnimation] method doesn’t block – I mean that the code implementation continues and the animation is done asynchronously.
So, actually, what is going on is that you go through all the loop iterations first and then the animation is done from 0.7 to 1.0…

Just use the setAnimationDidStopSelector without the “for” loop.

schwarz.alpha = 0.7;
[UIView beginAnimations:nil context:nil];
[UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
[UIView setAnimationDuration:1];
[UIView setAnimationDelegate:self];
[UIView setAnimationDidStopSelector:@selector(animationDidStop:finished:context:)];
schwarz.alpha = 0.1;
[UIView commitAnimations];

The catching method might be:

- (void)animationDidStop:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context {
/* Do your things here... */ }