How to change the targetContentOffset of a UICollectionView in Swift? - ios

Question

In my UIViewController I have a UICollectionView. The delegate is set properly. It just works fine. isPagingEnabled is set to true. But now I want to change the paging-positions I tried it within scrollViewWillEndDragging, because in the documentation it says:
Your application can change the value of the targetContentOffset parameter to adjust where the scrollview finishes its scrolling animation.
This functions is called properly but the only thing happens when I want to set a new Endpoint, the UICollectionView scrolls to 0.
This is my code:
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
print(scrollView.contentOffset, "actual Offset")
print(targetContentOffset.pointee, "future offset")
targetContentOffset.pointee = CGPoint(x: 100, y: 0)
print(targetContentOffset.pointee, "new future offset")
}
At the print("new future offset"), it prints the right value. So it seems the value is mutated after this function.

Answer 1

func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint,
withScrollingVelocity velocity: CGPoint) -> CGPoint
Description:
If you want the scrolling behavior to snap to specific boundaries, you
can override this method and use it to change the point at which to
stop. For example, you might use this method to always stop scrolling
on a boundary between items, as opposed to stopping in the middle of
an item.
Override this layout method instead of directly changing value of targetContentOffset.
If you want the scrolling behavior to snap to specific boundaries, you can override this method and use it to change the point at which to stop. For example, you might use this method to always stop scrolling on a boundary between items, as opposed to stopping in the middle of an item.
Docs:
https://developer.apple.com/documentation/uikit/uicollectionviewlayout/1617729-targetcontentoffset