使用自定义布局时未调用 sizeForItemAt 方法 [英] sizeForItemAt method is not calling when using custom layout

问题描述

我正在为我的集合视图使用自定义布局，但如果我使用自定义布局 sizeForItemAt 方法不会调用.

I am using custom layout for my collection view but if i use custom layout sizeForItemAt method is not calling.

我的自定义布局:

public class HorizontalCollectionViewLayout : UICollectionViewLayout {
    var itemSize = CGSize(width: 0, height: 0) {
        didSet {
            invalidateLayout()
        }
    }
    private var cellCount = 0
    private var boundsSize = CGSize(width: 0, height: 0)

    public override func prepare() {
        cellCount = self.collectionView!.numberOfItems(inSection: 0)
        boundsSize = self.collectionView!.bounds.size
    }
    public override var collectionViewContentSize: CGSize {
        let verticalItemsCount = Int(floor(boundsSize.height / itemSize.height))
        let horizontalItemsCount = Int(floor(boundsSize.width / itemSize.width))

        let itemsPerPage = verticalItemsCount * horizontalItemsCount
        let numberOfItems = cellCount
        let numberOfPages = Int(ceil(Double(numberOfItems) / Double(itemsPerPage)))

        var size = boundsSize
        size.width = CGFloat(numberOfPages) * boundsSize.width
        return size
    }

    public override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        var allAttributes = [UICollectionViewLayoutAttributes]()
        if cellCount > 0 {
        for i in 0...(cellCount-1) {
            let indexPath = IndexPath(row: i, section: 0)
            let attr = self.computeLayoutAttributesForCellAt(indexPath: indexPath)
            allAttributes.append(attr)
        }
        }
        return allAttributes
    }

    public override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        return computeLayoutAttributesForCellAt(indexPath: indexPath)
    }

    public override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        return true
    }

    private func computeLayoutAttributesForCellAt(indexPath:IndexPath)
        -> UICollectionViewLayoutAttributes {
            let row = indexPath.row
            let bounds = self.collectionView!.bounds

            let verticalItemsCount = Int(floor(boundsSize.height / itemSize.height))
            let horizontalItemsCount = Int(floor(boundsSize.width / itemSize.width))
            let itemsPerPage = verticalItemsCount * horizontalItemsCount

            let columnPosition = row % horizontalItemsCount
            let rowPosition = (row/horizontalItemsCount)%verticalItemsCount
            let itemPage = Int(floor(Double(row)/Double(itemsPerPage)))

            let attr = UICollectionViewLayoutAttributes(forCellWith: indexPath)

            var frame = CGRect(x: 0,y: 0,width: 0,height: 0)
            frame.origin.x = CGFloat(itemPage) * bounds.size.width + CGFloat(columnPosition) * itemSize.width
            frame.origin.y = CGFloat(rowPosition) * itemSize.height
            frame.size = itemSize
            attr.frame = frame

            return attr
    }
}

我在 viewDidLoad 方法中设置此布局:

And i am setting this layout at viewDidLoad method:

let itemWidth = 100
let itemHeight = 100
let horizontalCV = HorizontalCollectionViewLayout();
horizontalCV.itemSize = CGSize(width: itemWidth, height: itemHeight)

instagramCollection.collectionViewLayout = horizontalCV
self.instagramCollection.delegate=self
self.instagramCollection.dataSource=self

其他集合视图方法工作正常，例如 numberOfItemsInSection 或 cellForItemAt 等.但我无法为集合视图设置插图或单元格间距.

Other collection view methods are working fine like numberOfItemsInSection or cellForItemAt etc. But I can't set insets or cell spacing for my collection view.

我尝试了以下代码，以下方法未调用.

func collectionView(_ collectionView: UICollectionView,
                    layout collectionViewLayout: UICollectionViewLayout,
                    sizeForItemAt indexPath: IndexPath) -> CGSize {
    return CGSize.init(width: (instagramCollection.frame.width / 3.0), height: instagramCollection.frame.height / 2.0)
}


func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
    return UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
    return 10.0
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
    return 10.0
}

我也尝试设置 instets 和故事板的间距也没有奏效.

我的收藏视图现在对所有插图和间距使用零.

My collection view now using zero for all insets and spacing.

如何解决这个问题?

推荐答案

它不会在您使用自己的流程布局时被调用，请按照以下步骤解决:

It won't be called as you are using your own flow layout, as a work around follow these steps:

1- 定义你自己的协议

1- define your own protocol

protocol MyCustomCollectionLayoutDelegate: AnyObject {
    func collectionView(_ collectionView: UICollectionView, sizeForItem indexPath: IndexPath) -> CGSize
}

2- 在自定义布局中添加委托属性

2- Add a delegate property inside your custom layout

final class HorizontalCollectionViewLayout: UICollectionViewFlowLayout {


     weak var delegate: MyCustomCollectionLayoutDelegate?
     ....
}

3- 在你的 UICollectionViewController

class MyViewController: UICollectionViewController, MyCustomCollectionLayoutDelegate {

    var customLayout: HorizontalCollectionViewLayout? {
        let layout = collectionView?.collectionViewLayout as? DeviceDetailsCollectionLayout
        layout?.delegate = self
        return layout
    }

    func collectionView(_ collectionView: UICollectionView, sizeForItem indexPath: IndexPath) -> CGSize {
        return CGSize(width: 50, height: 60)
    }

}

4- 在自定义布局类中调用委托方法

4- call your delegate method inside your custom layout class

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

     let cellIndexPath = IndexPath(item: 0, section: 0)
     let customSize = delegate?.collectionView(collectionView, sizeForItem: cellIndexPath)

     // use your size ...

}

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