Swift 4.1 решение, которое упрощает повторное использование:
/// Protocol that simplifies custom page size configuration for UIScrollView.
/// Sadly, can not be done better due to protocol extensions limitations - https://stackoverflow.com/questions/39487168/non-objc-method-does-not-satisfy-optional-requirement-of-objc-protocol
/// - note: Set `.decelerationRate` to `UIScrollViewDecelerationRateFast` for a fancy scrolling animation.
protocol ScrollViewCustomHorizontalPageSize: UIScrollViewDelegate {
/// Custom page size
var pageSize: CGFloat { get }
/// Helper method to get current page fraction
func getCurrentPage(scrollView: UIScrollView) -> CGFloat
/// Helper method to get targetContentOffset. Usage:
///
/// func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
/// targetContentOffset.pointee.x = getTargetContentOffset(scrollView: scrollView, velocity: velocity)
/// }
func getTargetContentOffset(scrollView: UIScrollView, velocity: CGPoint) -> CGFloat
/// Must be implemented. See `getTargetContentOffset` for more info.
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>)
}
extension ScrollViewCustomHorizontalPageSize {
func getCurrentPage(scrollView: UIScrollView) -> CGFloat {
return (scrollView.contentOffset.x + scrollView.contentInset.left) / pageSize
}
func getTargetContentOffset(scrollView: UIScrollView, velocity: CGPoint) -> CGFloat {
let targetX: CGFloat = scrollView.contentOffset.x + velocity.x * 60.0
var targetIndex = (targetX + scrollView.contentInset.left) / pageSize
let maxOffsetX = scrollView.contentSize.width - scrollView.bounds.width + scrollView.contentInset.right
let maxIndex = (maxOffsetX + scrollView.contentInset.left) / pageSize
if velocity.x > 0 {
targetIndex = ceil(targetIndex)
} else if velocity.x < 0 {
targetIndex = floor(targetIndex)
} else {
let (maxFloorIndex, lastInterval) = modf(maxIndex)
if targetIndex > maxFloorIndex {
if targetIndex >= lastInterval / 2 + maxFloorIndex {
targetIndex = maxIndex
} else {
targetIndex = maxFloorIndex
}
} else {
targetIndex = round(targetIndex)
}
}
if targetIndex < 0 {
targetIndex = 0
}
var offsetX = targetIndex * pageSize - scrollView.contentInset.left
offsetX = min(offsetX, maxOffsetX)
return offsetX
}
}
Просто следуйте протоколу ScrollViewCustomPageSize в вашем делегате UIScrollView / UITableView / UICollectionView, и все готово, например ::
extension MyCollectionViewController: ScrollViewCustomPageSize {
var pageSize: CGFloat {
return 200
}
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
targetContentOffset.pointee.x = getTargetContentOffset(scrollView: scrollView, velocity: velocity)
}
}
Для необычной прокрутки я также рекомендую установить collectionView.decelerationRate = UIScrollViewDecelerationRateFast