滚动时，带有水平插入的集合视图单元格不会保持居中

Question

嘿，我有一个带有以下滚动行为的集合视图：

单元格之间需要间隔16磅，滚动时保持居中。您只能在演示中看到第一个和最后一个单元格保持居中。我的集合视图宽度与屏幕的宽度相同。在viewDidLoad中设置如下：

func setupCollectionView() {
        collectionView.delegate = self
        collectionView.dataSource = self
        collectionView.showsHorizontalScrollIndicator = false
        collectionView.showsVerticalScrollIndicator = false
        collectionView.register(UINib(nibName: "SubtopicCollectionCell", bundle: nil), forCellWithReuseIdentifier: "SubtopicCollectionCell")
        let flowLayout = UICollectionViewFlowLayout()
        flowLayout.scrollDirection = .horizontal
        flowLayout.minimumLineSpacing = 16
        collectionView.isPagingEnabled = true
        collectionView.setCollectionViewLayout(flowLayout, animated: false)
    }

各种委托方法如下：

func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 5
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell: SubtopicCollectionCell = collectionView.dequeueReusableCell(withReuseIdentifier: "SubtopicCollectionCell", for: indexPath) as! SubtopicCollectionCell
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: collectionView.frame.size.width * 0.78, height: collectionView.frame.size.height)
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
        return UIEdgeInsets(top: 0, left: 40, bottom: 0, right: 40)
    }

重要的是，下一个单元格的一部分显示在屏幕上，当前单元格居中（如演示中的第一个和最后一个单元格）。我该如何实现这种行为？

Answer 1

您可以在collectionViewLayout函数中使用以下简单计算来实现。

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAtIndex section: Int) -> UIEdgeInsets {

    let cellWidth = CellWidth * CellCount
    let spacingWidth = CellSpacing * (CellCount - 1)

    let leftInset = (collectionViewWidth - CGFloat(CellWidth + SpacingWidth)) / 2
    let rightInset = leftInset

    return UIEdgeInsetsMake(0, leftInset, 0, rightInset)
}

不要忘记实施以下协议

UICollectionViewDelegateFlowLayout