Question

我的collectionView有问题。其实我有这个算法：
-第一个单元格的宽度是screen_width / 2
-第二个单元格的宽度为：screen_width
-第三个单元格的宽度为screen_width / 2
-第四个单元格的宽度是：screen_width。

以此类推。

这是我在方法中的代码

- (CGSize)collectionView:(UICollectionView *)collectionView
                  layout:(UICollectionViewLayout *)collectionViewLayout
  sizeForItemAtIndexPath:(NSIndexPath *)indexPath:

    userStory.typePhotoStory = ( (indexPath.row + 1) % 3) == 0 ? @"landscape" : ((indexPath.row + 1) % 3) == 1 ? @"portrait": @"landscape";
    if ([userStory.typePhotoStory isEqualToString:@"portrait"]) {
        cellSizeFinalWidth = cellSize / 2 ;
        cellSizeFinalHeight = cellSizeFinalWidth + 20 ;
    } else {
        cellSizeFinalWidth = cellSize + padding ;
        cellSizeFinalHeight = cellSize / 2 + 20 ;
    }
}

但是我看到，第一个和第三个单元格位于屏幕的中央，而不是从左侧开始。请帮助我解决这个问题？

Answer 1

您可以直接使用此代码，

创建一个新文件，并将其粘贴到下面的代码中以用于自定义布局。

import UIKit

protocol NewLayoutDelegate: class {
    func collectionView(_ collectionView:UICollectionView, SizeOfCellAtIndexPath indexPath:IndexPath) -> CGSize
}


class NewFlowLayout: UICollectionViewFlowLayout {

    weak var delegate : NewLayoutDelegate?

    fileprivate var numberOfColumns = 1
    fileprivate var cellPadding: CGFloat = 6
    fileprivate var cache = [UICollectionViewLayoutAttributes]()


    fileprivate var contentHeight: CGFloat = 0

    fileprivate var contentWidth: CGFloat {
        guard let collectionView = collectionView else {
            return 0
        }
        let insets = collectionView.contentInset
        return collectionView.bounds.width - (insets.left + insets.right)
    }

    override var collectionViewContentSize: CGSize {
        return CGSize(width: contentWidth, height: contentHeight)
    }

    override func prepare() {
        super.prepare()

        guard cache.isEmpty == true, let collectionView = collectionView else {
            return
        }

        let xOffset : CGFloat = 0
        let column = 0
        var yOffset = [CGFloat](repeating: 0, count: numberOfColumns)

        for item in 0 ..< collectionView.numberOfItems(inSection: 0) {

            let indexPath = IndexPath(item: item, section: 0)
            let aSize = delegate?.collectionView(collectionView, SizeOfCellAtIndexPath: indexPath)
            let height = cellPadding * 2 + (aSize?.height)!
            let frame = CGRect(x: xOffset, y: yOffset[column], width: (aSize?.width)!, height: height)
            let insetFrame = frame.insetBy(dx: cellPadding, dy: cellPadding)

            let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
            attributes.frame = insetFrame
            cache.append(attributes)

            contentHeight = max(contentHeight, frame.maxY)
            yOffset[column] = yOffset[column] + height


        }
    }

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {

        var visibleLayoutAttributes = [UICollectionViewLayoutAttributes]()

        for attributes in cache {
            if attributes.frame.intersects(rect) {
                visibleLayoutAttributes.append(attributes)
            }
        }
        return visibleLayoutAttributes
    }

    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        return cache[indexPath.item]
    }

}

在您的控制器文件中

import UIKit

class NewCell: UICollectionViewCell {

}

class NewViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, NewLayoutDelegate {

    @IBOutlet weak var myCollectionView: UICollectionView!

    override func viewDidLoad() {
        super.viewDidLoad()

        myCollectionView.collectionViewLayout = NewFlowLayout()

        if let layout = myCollectionView.collectionViewLayout as? NewFlowLayout {
            layout.delegate = self
        }

    }

    // Do size logic here
    func collectionView(_ collectionView: UICollectionView, SizeOfCellAtIndexPath indexPath: IndexPath) -> CGSize {

        let insets = collectionView.contentInset

        if indexPath.item % 2 == 0 {
            return CGSize(width: (collectionView.frame.size.width - (insets.left + insets.right))/2,
                          height: 60)
        }

        return CGSize(width: collectionView.frame.size.width - (insets.left + insets.right),
                      height: 60)
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 10
    }

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

        return cell
    }
}

输出

UICollectionView单元格为什么居中？

1 个答案: