for family in UIFont.familyNames {
            
            for font in UIFont.fontNames(forFamilyName: family) {
                
                print(font)
                
            }
            
        }

import UIKit

class ViewController: UIViewController {

    lazy var contentLabel = UILabel()
    lazy var changeBtn = UIButton()
    var tag: Int = 0
    
    
    override func viewDidLoad() {
        super.viewDidLoad()

       /* for family in UIFont.familyNames {
            
            for font in UIFont.fontNames(forFamilyName: family) {
                
                print(font)
                
            }
            
        }*/
        
        self.view.backgroundColor = UIColor.black
        contentLabel.frame = CGRect(x: 10, y:20, width:UIScreen.main.bounds.size.width - 20, height: 200)
        contentLabel.numberOfLines = 0
        contentLabel.textColor = UIColor.white
        contentLabel.font = UIFont.systemFont(ofSize: 20)
        self.view.addSubview(contentLabel)
        let content: String = "30 Days Swift\n\n 目前授权个人免费非商业使用\n\n 所以捐款了1元下了3款字体用来做试验\n\n 分别是造字工房劲黑，致黑和童心；"
        contentLabel.text = content
        
        changeBtn.backgroundColor = UIColor.orange
        changeBtn.frame.size = CGSize(width: 100, height: 100)
        changeBtn.frame.origin = CGPoint(x: UIScreen.main.bounds.size.width/2 - 50, y: UIScreen.main.bounds.size.height - 120)
        changeBtn.setTitle("改变字体", for: .normal)
        changeBtn.layer.masksToBounds = true
        changeBtn.layer.cornerRadius = 50.0
        changeBtn.addTarget(self, action: #selector(changeFont), for: .touchUpInside)
        self.view.addSubview(changeBtn)
     }
    
    //MARK: - 点击事件
    func changeFont() {
        var fontName:String
        switch tag {
        case 0:
            fontName = "MFQingShu_Noncommercial-Regular"
            tag = 1
        case 1:
            fontName = "MFYueYuan_Noncommercial-Regular"
            tag = 2
        case 2:
            fontName = "MFWenYan_Noncommercial-Regular"
            tag = 3
        default:
            fontName = "AppleSDGothicNeo-Regular"
            tag = 0
        }
        
        contentLabel.font = UIFont.init(name: fontName, size: 20)
    }
    
    

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}