Swift之UICollectionView瀑布流

相信大家对UICollectionView的使用都不陌生了，这里我要简单说下瀑布流的功能实现，希望有助于大家对瀑布流的实现逻辑有所加深理解，先上效果图

效果图

WaterFallLayout 类

import Foundation
import UIKit

class WaterFallLayout: UICollectionViewFlowLayout {
    // item个数
    let itemCount: Int
    // items的布局信息
    var attributeArray: Array<UICollectionViewLayoutAttributes>?
    
    // 实现必要的构造方法
    required init?(coder: NSCoder) {
        itemCount = 0
        super.init(coder: coder)
    }
    
    // 自定义一个初始化构造方法
    init(itemCount: Int) {
        self.itemCount = itemCount
        super.init()
    }
    
    // 准备方法
    override func prepare() {
        // 调用父类的准备方法
        super.prepare()
        // 设置为竖直布局
        self.scrollDirection = .vertical
        // 初始化数组
        attributeArray = Array<UICollectionViewLayoutAttributes>()
        // 先计算每个item的宽度，默认为两列布局
        let WIDTH = (UIScreen.main.bounds.size.width - self.minimumInteritemSpacing) / 2
        // 定义一个元组表示每一列的动态高度
        var queueHeight:(one: Int, two: Int) = (0,0)
        // 进行循环设置
        for index in 0..<self.itemCount {
            // 设置indexPath，默认一个分区
            let indexPath = IndexPath(item: index, section: 0)
            // 创建布局属性类
            let attris = UICollectionViewLayoutAttributes(forCellWith: indexPath)
            // 随机一个高度在80到90之间的值
            let height: Int = Int(arc4random() % 110 + 80)
            // 哪列高度小就把它放那列下面
            // 标记那一列
            var queue = 0
            if queueHeight.one <= queueHeight.two {
                queueHeight.one += (height + Int(self.minimumInteritemSpacing))
                queue = 0
            } else {
                queueHeight.two += (height+Int(self.minimumInteritemSpacing))
                queue = 1
            }
            // 设置item的位置
            let tmpH = queue == 0 ? queueHeight.one-height : queueHeight.two-height
            attris.frame = CGRect(x: (self.minimumInteritemSpacing+WIDTH)*CGFloat(queue), y: CGFloat(tmpH), width: WIDTH, height: CGFloat(height))
            // 添加到数组中
            attributeArray?.append(attris)
        }
        // 以最大一列的高度计算每个item高度的中间值，这样就可以保证滑动范围的正确
        if queueHeight.one <= queueHeight.two {
            self.itemSize = CGSize(width: WIDTH, height: CGFloat(queueHeight.two*2/self.itemCount)-self.minimumLineSpacing)
        } else {
            self.itemSize = CGSize(width: WIDTH, height: CGFloat(queueHeight.one*2/self.itemCount)-self.minimumLineSpacing)
        }
    }
    // 将设置好存放每个item的布局信息返回
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        return attributeArray
    }
}

ViewController 类

import UIKit

class ViewController: UIViewController, UICollisionBehaviorDelegate, UICollectionViewDataSource, UICollectionViewDelegate {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        let layout = WaterFallLayout(itemCount: 30)
        let collectionView = UICollectionView(frame: self.view.frame, collectionViewLayout: layout)
        collectionView.delegate = self
        collectionView.dataSource = self
        collectionView.register(NSClassFromString("UICollectionViewCell"), forCellWithReuseIdentifier: "itemID")
        self.view.addSubview(collectionView)
        
    }

    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 30
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "itemID", for: indexPath)
        cell.backgroundColor = UIColor(red: CGFloat(arc4random()%255)/255, green: CGFloat(arc4random()%255)/255, blue: CGFloat(arc4random()%255)/255, alpha: 1)
        return cell
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        print("点击了第\(indexPath.row)个item")
    }

}

参考文章：
swift4-UICollectionView(实现瀑布流)