UICollectionView Horizontal Paging not centered

Question

I have a horizontal scrolling collectionView with each cell the size of the view. When I page through the collectionView it doesn\'t page by cell. The cells aren\'t in the c

Answer 1

If you're after the behaviour of collectionView.isPagingEnabled (so with 'proper inertia feeling' etc) but without wrong offsets when setting a contentInset or spacing, this is what you need:

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer) {
    let itemWidth = cellSize.width + spacing
    let inertialTargetX = targetContentOffset.pointee.x
    let offsetFromPreviousPage = (inertialTargetX + collectionView.contentInset.left).truncatingRemainder(dividingBy: itemWidth)
    
    // snap to the nearest page
    let pagedX: CGFloat
    if offsetFromPreviousPage > itemWidth / 2 {
        pagedX = inertialTargetX + (itemWidth - offsetFromPreviousPage)
    } else {
        pagedX = inertialTargetX - offsetFromPreviousPage
    }
    
    let point = CGPoint(x: pagedX, y: targetContentOffset.pointee.y)
    targetContentOffset.pointee = point
}