Key value Observing during UIView Animations

Question

Hi,

I'm animating the center property of a view in my program. During the animation, I need notifications when center hits a particular value.

I tried adding the myself as a key value observer for the center property of the view . However, I only get notified when the animation begins. So I'm unable to detect if/when the object passes through my point of interest.

Is there a way to do this through KVO or any other method?

Thanks!

Answer 1

You can retrieve the values representing the current state of the UIView's animating layer by accessing its presentation layer. This can be done using code like the following:

CGPoint currentCenter = [[view.layer presentationLayer] center];

Unfortunately, the presentation layer's properties are not KVO-compliant, so the best way I can think of for tracking the current value is to keep polling the presentation layer until it gets near the location you want.