设置UI界面用swifet

用Swift写一个登录界面
首先在AppDelegate初始化:

    //初始化
    self.window?.rootViewController = UINavigationController (rootViewController: ViewController())

viewcontroller里写:
var img : UIImageView? = nil

var text : UITextField? = nil
var text2 : UITextField? = nil

var btn : UIButton?

var lab1 : UILabel?
然后:

self.view.backgroundColor = .white
self.navigationItem.title = "123"

    //左按钮
    self.navigationItem.leftBarButtonItem = UIBarButtonItem (barButtonSystemItem: UIBarButtonSystemItem.add, target: self, action: nil)
    
    //添加图片
    img = UIImageView(frame: CGRect(x: 160, y: 100, width: 80, height: 80))
    img?.image = UIImage(named: "未选中的副本")
    self.view.addSubview(img!)
    
    
    
    
    //文本框
    text = UITextField(frame: CGRect(x: 50, y: 250, width: 300, height: 50))
    text?.backgroundColor = .green
    //提示文字
    text?.placeholder = "222"
    self.view.addSubview(text!)
    
    text2 = UITextField(frame: CGRect(x: 50, y: 310, width: 300, height: 50))
    text2?.backgroundColor = .green
    self.view.addSubview(text2!)
    
    
    
    //button
    btn = UIButton(frame: CGRect(x: 70, y: 380, width: 250, height: 50))
    btn?.backgroundColor = .blue
    btn?.setTitle("12345", for: .normal)
    self.view.addSubview(btn!)
    
    
    
    //label
    lab1 = UILabel(frame: CGRect(x: 300, y: 450, width: 100, height: 30))
    lab1?.text = "123"
    self.view.addSubview(lab1!)