核心动画和UIImageView返回起始位置

Question

I have a UIImageView that I'm moving across the screen based on a user swiping. I accomplish this using Core Animation:

 [UIView beginAnimations:nil context:nil];
 [UIView setAnimationDuration:1.0];

 movingView.frame = theRect;

 [UIView commitAnimations];

It always starts out fine, but partway through going from its original location to the "theRect" location, it stops and the UIImageView jumps back to its starting point. It's never at the same point. Sometimes gets almost all the way through before jumping back, sometimes only barely moving then jumping back. No other code is running after this. I've tried changing the duration and it doesn't seem to matter.

If I add in:

 [UIView setAnimationDidStopSelector:@selector(completeAnimation:finished:context:)];
 [UIView setAnimationDelegate:self];

Then it actually delays until the Duration is complete and runs the selector, even if the image itself stops and returns to its starting point almost immediately.

Hopefully someone can give me some hints at what might be going on here.

Answer 1

If using autolayout, you can animate the changing of the constraint, not animating the change of the frame (because when constraints are reapplied, the original location will be restored). See Animating an image view to slide upwards for an example.