Swift - 使用网格（UICollectionView）进行流布局

import UIKit

class ViewController: UICollectionViewController {
    
    //课程名称和图片，每一门课程用字典来表示
    let courses = [
        ["name":"Swift","pic":"swift.png"],
        ["name":"OC","pic":"oc.jpg"],
        ["name":"java","pic":"java.png"],
        ["name":"php","pic":"php.jpeg"]
    ]
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 已经在界面上设计了Cell并定义了identity，不需要注册CollectionViewCell
        //self.collectionView.registerClass(UICollectionViewCell.self,
        //  forCellWithReuseIdentifier: "DesignViewCell")
        
        self.collectionView?.backgroundColor = UIColor.white
    }
    
    // CollectionView行数
    override func collectionView(_ collectionView: UICollectionView,
                                 numberOfItemsInSection section: Int) -> Int {
        return courses.count;
    }
    
    // 获取单元格
    override func collectionView(_ collectionView: UICollectionView,
                cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        // storyboard里设计的单元格
        let identify:String = "DesignViewCell"
        // 获取设计的单元格，不需要再动态添加界面元素
        let cell = (self.collectionView?.dequeueReusableCell(
            withReuseIdentifier: identify, for: indexPath))! as UICollectionViewCell
        // 从界面查找到控件元素并设置属性
        (cell.contentView.viewWithTag(1) as! UIImageView).image =
            UIImage(named: courses[indexPath.item]["pic"]!)
        (cell.contentView.viewWithTag(2) as! UILabel).text =
            courses[indexPath.item]["name"]
        return cell
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}