每次滾動視圖結束時居中顯示一個collectionView的單元格

Question

我有一個collectionView，並且它的scrollview有一個擴展名，它可以幫助我像這樣獲得我的單元格20像素（來自下一個單元格的最小空間）右側：

現在我想改變我的擴展，該中心以這樣的容器：

我的分機是這樣的：（如果我可以與任何其他的方式做到隨時告訴它）

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

我想說

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

，或者更好地

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 
)