you can just use UIscrollView Delegate methods Apple Documentation and this an example
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
if(!decelerate){
// Do something
}
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
// Do something
}
for your problem you can apply your behaviour on scrollViewDidEndDragging