How to make UIScrollView send scrollViewDidScroll messages during animations

Question

When the user manually scrolls through my UIScrollView, the scrollViewDidScroll method of my delegate gets called repeatedly during the animation, with newly updated values

Answer 1

Thanks to Fichek's hint, I have gotten this to work. Like Fichek said, you don't get any notifications of changed properties during animation. So the trick is, to make sure that anything that depends on the changed property is also animated at the same time. You need to setup their animations in the same block as the original property. If you then set the "UIViewAnimationOptionAllowUserInteraction" on the animation, then any ongoing user interaction of the same properties will still work - and surprisingly well, I have to say.

For my concrete case - to keep a dragged view stationary, while the UIScrollView scrolls underneath - here is how I setup my animation:

[UIView animateWithDuration:0.5 delay:0
                    options:UIViewAnimationOptionAllowUserInteraction
                 animations:^{
    [theScrollView setContentOffset:offset];
    // compute newCenter from the new offset
    theDraggedView.center = newCenter;
} completion:^(BOOL finished) {}];