swift4.2 打印所有系统字体

    func showAllFonts(){
        let familyNames = UIFont.familyNames
        
        var index:Int = 0
        
        for familyName in familyNames {
            
            let fontNames = UIFont.fontNames(forFamilyName: familyName as String)
            for fontName in fontNames
            {
                index += 1
                
                print("第 \(index) 个字体，字体font名称：\(fontName)")
            }
        }
    }