Paging Swift上的UICollectionView大小调整问题

Question

在启用了部分和分页的情况下面对UICollectionview大小调整问题。 目前，我希望每个部分显示7列和6行，并且单元格的大小固定，所以我创建如下。

        var margin: CGFloat = 10
        let cellsPerRow = 7
        let numberOfRows = 6;
        let cellHeight = 50
        let size = UIScreen.main.bounds.size.width - CGFloat(cellsPerRow*cellHeight)
        margin = size/CGFloat(cellsPerRow);

        collectionView = UICollectionView(frame: CGRect(x: 0, y: 0, width: self.frame.size.width, height: 300), collectionViewLayout: UICollectionViewFlowLayout.init())


        guard let flowLayout = collectionView?.collectionViewLayout as? UICollectionViewFlowLayout else { return }
        flowLayout.minimumInteritemSpacing = margin
        flowLayout.minimumLineSpacing = 0
        flowLayout.sectionInset = UIEdgeInsets(top: margin, left: margin, bottom: margin, right: margin)
        flowLayout.scrollDirection = UICollectionViewScrollDirection.vertical

        collectionView.register(MyCollectionViewCell.self, forCellWithReuseIdentifier: "collectionCell")
        collectionView.isPagingEnabled = true;
        collectionView.dataSource = self;
        collectionView.delegate = self;


func numberOfSections(in collectionView: UICollectionView) -> Int {
    return 20;
}

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 42;
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    //return collectionView.dequeueReusableCell(withReuseIdentifier: "collectionCell", for: indexPath)
     let cell = collectionView.dequeueReusableCell(withReuseIdentifier:"collectionCell", for: indexPath) as! MyCollectionViewCell
    cell.backgroundColor = UIColor.random()
    return cell;
}

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

    let flowLayout = collectionView.collectionViewLayout as! UICollectionViewFlowLayout
    let marginsAndInsets = flowLayout.sectionInset.left + flowLayout.sectionInset.right + flowLayout.minimumInteritemSpacing * CGFloat(cellsPerRow - 1)
    let itemWidth = ((collectionView.bounds.size.width - marginsAndInsets) / CGFloat(cellsPerRow)).rounded(.down)
    return CGSize(width: itemWidth, height: itemWidth)

}

我想在屏幕上只显示集合视图的一个部分。最初，它工作正常但经过一些滚动（在第6至第7节之后）我面临着尺寸问题。它向我展示了上一节的一些部分。请参阅附带的问题截图。

请帮帮我。提前谢谢。

Answer 1

对于复杂的分页，最好使用scrollView Delegate： scrollViewWillEndDragging(_:withVelocity:targetContentOffset:)（见documentation

在您的代码中，它将如下所示：

    func scrollViewWillEndDragging(_ scrollView: UIScrollView, 
                                   withVelocity velocity: CGPoint, 
                            targetContentOffset: UnsafeMutablePointer<CGPoint>) {

        let pageHeight : CGFloat = /* number of rows */ 6 * /* height of row */ 50 + /*  number of interspacing */ 5 * /* interspacing */ 10

        //This is where the scrollview Gonna stops
        let naturalDestination = targetContentOffset.pointee.y

        //Round it to the nearest page
        let computedDestination = round(targetContentOffset.pointee.y / pageHeight) * pageHeight

        //Edit the targetOffset
        targetContentOffset.pointee.y =  computedDestination

    }