Disable scrollViewDidScroll: when scrolling UICollectionView - iOS

Question

I have implemented scrollViewDidScroll: inside my viewcontroller to cause some animations when I scroll the view up and down.

However, when I scroll my collectionview inside the viewcontroller (horizontally) it messes up with my animation inside scrollViewDidScroll:

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    newAlpha = 1 - scrollView.contentOffset.y / 200;
    self.introImageView.alpha = newAlpha;
    //... -> prevent scrolling when collectionview is scrolled
}

How do I prevent calling scrollViewDidScroll: when scrolling my collectionview horizontally?

Answer 1

The best way is not to disable the delegate method, but make sure to only call that code when it's called by your scrollview. Here's an example

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    if (scrollView == self.myScrollView) {
        newAlpha = 1 - scrollView.contentOffset.y / 200;
        self.introImageView.alpha = newAlpha;
    } else {
       //collectionView would fall here
    }

}

Answer 2

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    if ([scrollView isKindOfClass:[UICollectionView class]] == NO) {
        newAlpha = 1 - scrollView.contentOffset.y / 200;
        self.introImageView.alpha = newAlpha;
        //... -> prevent scrolling when collectionview is scrolled
    }
}