设置集合视图单元格的动态宽度时出现问题

Question

我正在尝试动态设置集合视图单元格的宽度。最初它没有按预期渲染。但是当我点击单元格时，它会根据我的需要进行调整。这是我写的代码：

代码

import UIKit

class ViewController: UIViewController,UICollectionViewDelegate,UICollectionViewDataSource {

    @IBOutlet weak var collView: UICollectionView!


    var tasksArray = ["To Do", "SHOPPING","WORK"]
    var selectedIndex = Int()

    override func viewDidLoad() {
        super.viewDidLoad()
        let layout = collView?.collectionViewLayout as! UICollectionViewFlowLayout
        layout.itemSize = UICollectionViewFlowLayout.automaticSize
        layout.estimatedItemSize = CGSize(width: 93, height: 40)
        // Do any additional setup after loading the view, typically from a nib.
    }
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return tasksArray.count
    }
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! CollectionViewCell
        cell.lblName.text = tasksArray[indexPath.row]
        if selectedIndex == indexPath.row
        {
            cell.backgroundColor = UIColor.lightGray
        }
        else
        {
            cell.backgroundColor = UIColor.white
        }
        cell.layer.borderWidth = 1
        cell.layer.cornerRadius = cell.frame.height / 2
        return cell
    }
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        selectedIndex = indexPath.row
        self.collView.reloadData()
    }
}

这里我附上了点击前和点击后的两张图片，以便您轻松理解

[！[这是我点击之前的图像

在细胞上] 2 ] 2

所以请告诉我我的代码有什么问题

Answer 1

CollectionViewCell在覆盖 函数内部preferredLayoutAttributesFitting，单元格有机会指示其首选属性，包括我们使用自动布局计算的大小。

 override func preferredLayoutAttributesFitting(_ layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes {
    setNeedsLayout()
    layoutIfNeeded()
    let size = contentView.systemLayoutSizeFitting(layoutAttributes.size)
    var frame = layoutAttributes.frame
    frame.size.width = ceil(size.width)
    layoutAttributes.frame = frame
    return layoutAttributes
}