UICollectionViewCell平分屏幕宽度

平分屏幕宽度的UICollectionViewCell

1. 重写layout
2. xib定义cell 且设置约束
3. vc中代码创建UICollectionView, 实现代理

• 重写layout

class NoGapLayout: UICollectionViewFlowLayout {
    
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        
        guard let attributes = super.layoutAttributesForElements(in: rect) else {
            return nil
        }
        
        if attributes.count == 0 {
            return attributes
        }
        
        let cellSpace = minimumInteritemSpacing
        let rightInset = sectionInset.right
        
        for i in 1..<attributes.count {
            
            ///1.当前attribute
            let currentAttribute = attributes[I]
            
            ///2.上一个attributes
            let prevLayoutAttribute = attributes[i - 1]
            
            ///3.前一个cell的最右边
            let origin = prevLayoutAttribute.frame.maxX
            
            ///4.如果当前一个cell的最右边加上我们想要的间距加上当前cell的宽度依然在contentSize中，我们改变当前cell的原点位置;
            ///不加这个判断的后果是，UICollectionView只显示一行，原因是下面所有cell的x值都被加到第一行最后一个元素的后面了
            if(origin + cellSpace + rightInset + currentAttribute.frame.size.width <= collectionViewContentSize.width) {
                var frame = currentAttribute.frame
                frame.origin.x = origin + cellSpace
                currentAttribute.frame = frame
            }

        }
        return attributes
    }
}

• 定义cell

• vc中代码

import UIKit

var rect: CGRect = .zero
let col: CGFloat = 3
let insetSpaces: CGFloat = 0
let cellSpace: CGFloat = 0

class LoadXibCellVC: UIViewController {

    ///collectionview
    fileprivate lazy var cv: UICollectionView = {[unowned self] in
        let layout: UICollectionViewFlowLayout = NoGapLayout()
        layout.minimumLineSpacing = 5
        layout.minimumInteritemSpacing = cellSpace
        layout.sectionInset = UIEdgeInsets(top: 5, left: insetSpaces, bottom: 5, right: insetSpaces)

        let v = UICollectionView(frame: self.view.bounds, collectionViewLayout: layout)
        v.backgroundColor = .systemRed
        v.delegate = self
        v.dataSource = self
        v.register(UINib(nibName: "XibCell", bundle: nil), forCellWithReuseIdentifier: "XibCell")
        self.view.addSubview(v)

        return v
    }()
    
    var items = [String]()
   
    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
        for name in 0...31 {
            var str = ""
            for i in 0...name {
                str.append("g\(i)")
            }
            items.append(str)
        }
   
        self.cv.reloadData()
    }
}

extension LoadXibCellVC: UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return items.count
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "XibCell", for: indexPath) as! XibCell
        
        cell.txt = items[indexPath.item]
        return cell
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        
        let w = (collectionView.width-2*insetSpaces-(col-1)*cellSpace)/col
        let h = w * 4 / 3
        
        let itemSize = CGSize(width: (w), height: (h))
        return itemSize
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        DebugLog(indexPath.item)
    }
}