每當滾動視圖結束時，將collectionView的單元格居中

Question

我有一個collectionView，並且它的scrollview有一個擴展，它可以幫助我在屏幕的右邊獲得20像素（下一個單元格的最小空間），如下所示：

現在，我想更改擴展名以將其居中放置在容器中，如下所示：

我的擴展名是：（如果我可以用其他任何方式做到這一點，請告訴我）

extension MyProject : UIScrollViewDelegate
{
    func scrollViewWillEndDragging(scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>)
    {
        let layout = self.collectionView?.collectionViewLayout as! UICollectionViewFlowLayout
        let cellWidthIncludingSpacing = layout.itemSize.width + layout.minimumLineSpacing

        var offset = targetContentOffset.memory
        let index = (offset.x + scrollView.contentInset.left) / cellWidthIncludingSpacing
        let roundedIndex = round(index)

        offset = CGPoint(x: roundedIndex * cellWidthIncludingSpacing - scrollView.contentInset.left, y: -scrollView.contentInset.top)
        targetContentOffset.memory = offset
    }
}

Answer 1

我會說

offset = CGPoint(
  x: roundedIndex * cellWidthIncludingSpacing - scrollView.contentInset.left + cellWithIncludingSpacing / 2 - scrollView.bounds.size.width / 2,
  y: -scrollView.contentInset.top
)

或者，考慮contentInset更好

let visibleWidth = scrollView.bounds.size.width
  - scrollView.contentInset.left
  - scrollView.contentInset.right
offset = CGPoint(
  x: roundedIndex * cellWidthIncludingSpacing
    - scrollView.contentInset.left
    + layout.itemSize.width / 2
    - visibleWidth / 2,
  y: -scrollView.contentInset.top
)