Swift 3 - 创建collectionView(系统流水布

import UIKit

private let CollectionCellId = "CollectionCell"

class ViewController: UIViewController {

    //懒加载 collectionView
    fileprivate lazy var collectionView : UICollectionView = UICollectionView(frame: CGRect.zero, collectionViewLayout: UICollectionViewFlowLayout())
    
    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(collectionView)
        collectionView.frame = view.bounds
        collectionView.backgroundColor = UIColor(red: 244/255.0, green: 244/255.0, blue: 244/255.0, alpha: 1)
        collectionView.dataSource = self;
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: CollectionCellId) //注册cell
        
        //设置流水布局 layout
        let layout = collectionView.collectionViewLayout as! UICollectionViewFlowLayout
        layout.itemSize = CGSize(width: 120 , height: 120)
        layout.minimumLineSpacing = 2  //行间距
        layout.minimumInteritemSpacing = 2  //列间距
        layout.scrollDirection = .horizontal //滚动方向
        
        collectionView.isPagingEnabled = true  //设置分页效果
        collectionView.showsHorizontalScrollIndicator = false  //隐藏水平滚动条
        

    }


}

//MARK:- UICollectionViewDataSource
extension ViewController : UICollectionViewDataSource{
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 100;
    }
   
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: CollectionCellId, for: indexPath)
        
        let R = (arc4random() % 256)
        let G = (arc4random() % 256)
        let B = (arc4random() % 256)
        
        cell.backgroundColor = UIColor(red: CGFloat(R)/255, green: CGFloat(G)/255, blue: CGFloat(B)/255, alpha: 1.0)
        
        return cell
        
        
    }
    
    
    
    
}