不多BB，直接进入正题。

我采用UICollectionView实现瀑布流效果。

swift瀑布流.png

首先新建一个类，该类继承自 UICollectionViewFlowLayout
然后创建几个常用变量：

 /** 默认列数 */
    private(set) var ColumnCountDefault : Int = 3
    /** 每一列之间的间距 垂直 */
    private(set) var ColumnMargin : CGFloat = 10.0
    /** 每一行之间的间距 水平方向 */
    private(set) var ItemMargin : CGFloat = 10.0
    /** 边缘间距 */
    private(set) var EdgeInsetsDefault : UIEdgeInsets = UIEdgeInsetsMake(10, 10, 10, 10)
    
    //懒加载
    //存放所有cell的布局属性
    lazy var attrsArray = [UICollectionViewLayoutAttributes]()
    //存放所有列的当前高度
    lazy var columnHeightsAry = [CGFloat]() 

第一步：初始化

override func prepare() {
        super.prepare()
        //清除高度
        columnHeightsAry.removeAll()
        
        for _ in 0 ..< ColumnCountDefault {
            columnHeightsAry.append(EdgeInsetsDefault.top)
        }
        
        //清除所有的布局属性
        attrsArray.removeAll()
        
        let sections : Int = (self.collectionView?.numberOfSections)!
        print("分区有\(sections)个")
        
        for num in 0 ..< sections {
            let count : Int = (self.collectionView?.numberOfItems(inSection: num))!//获取分区0有多少个item
            for i in 0 ..< count {
                let indexpath : NSIndexPath = NSIndexPath.init(item: i, section: num)
                let attrs = self.layoutAttributesForItem(at: indexpath as IndexPath)!
                
                attrsArray.append(attrs)
            }
        }
    }

第二步：根据indexPath位置返回cell对应的布局属性

override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        
        let attrs = UICollectionViewLayoutAttributes.init(forCellWith: indexPath)
        let collectionWidth = self.collectionView?.frame.size.width
        
        //获得所有item的宽度
        let __W = (collectionWidth! - EdgeInsetsDefault.left - EdgeInsetsDefault.right - CGFloat(ColumnCountDefault-1) * ColumnMargin) / CGFloat(ColumnCountDefault)
        let __H = 50 + arc4random_uniform(100)
        
        //找出高度最短那一列
        var dextColum : Int = 0
        var mainH = columnHeightsAry[0]
        
        for i in 1 ..< ColumnCountDefault{
            //取出第i列的高度
            let columnH = columnHeightsAry[i]
            
            if mainH > columnH {
                mainH = columnH
                dextColum = i
            }
        }
        
        print(dextColum)
        
        let x = EdgeInsetsDefault.left + CGFloat(dextColum) * (__W + ColumnMargin)
        var y = mainH
        
        if y != EdgeInsetsDefault.top{
            y = y + ItemMargin
        }
        attrs.frame = CGRect(x: x, y: y, width: __W, height: CGFloat(__H))
        //更新最短那列高度
        columnHeightsAry[dextColum] = attrs.frame.maxY
        print("frame\(attrs.frame)")
        return attrs
    }

第三步 ： 返回所有列的高度

override var collectionViewContentSize: CGSize {
        
        var maxHeight = columnHeightsAry[0]
        
        for i in 1 ..< ColumnCountDefault {
            let columnHeight = columnHeightsAry[i]
            
            if maxHeight < columnHeight {
                maxHeight = columnHeight
            }
        }
        
        return CGSize.init(width: 0, height: maxHeight + EdgeInsetsDefault.bottom)
    }

第四步 ：返回collection的item的frame

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

最后在Controller中实现

override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = UIColor.white
        
        //布局
        let layout = NDCollectionView()
        
        //创建collectionView
        let collectionView = UICollectionView.init(frame: self.view.bounds, collectionViewLayout: layout)
        view.addSubview(collectionView)
        
        collectionView.dataSource = self
        collectionView.delegate = self
        collectionView.backgroundColor = UIColor.white
        
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: shopID)
    }


实现代理方法
extension ViewController : UICollectionViewDataSource, UICollectionViewDelegate {
    
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 3
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 10
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: shopID, for: indexPath)
        
        cell.backgroundColor = UIColor.red
        
        return cell
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        
    }
    
}

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