打开模拟器时，我的应用程序上出现黑屏

如何解决打开模拟器时，我的应用程序上出现黑屏

我正在通过编码制作一个应用程序（因此StoryBoard中没有任何ViewController），但是当我尝试构建我的应用程序时，会出现白屏，然后立即出现黑屏。

没有线程错误。

有人可以帮助我吗？ 谢谢

这是代码：

导入UIKit 导入FirebaseAuth

LoginViewController类：UIViewController {

private let scrollView: UIScrollView = {
    let scrollView = UIScrollView()
    
    scrollView.clipsToBounds = true
    
    return scrollView
}()

private let logoView: UIImageView = {
    let logoView = UIImageView()
    logoView.image = UIImage(named: "logo")
    logoView.contentMode = .scaleAspectFit
    return logoView
}()

private let emailField: UITextField = {
    let field = UITextField()
    
    field.autocapitalizationType = .none
    field.autocorrectionType = .no
    field.returnKeyType = .continue
    field.layer.cornerRadius = 12
    field.layer.borderWidth = 1
    field.layer.borderColor = UIColor.lightGray.cgColor
    field.placeholder = "Email Address"
    field.leftView = UIView(frame: CGRect(x: 0,y: 0,width: 10,height: 0))
    field.leftViewMode = .always
    field.backgroundColor = .white
    
    return field
} ()

private let passwordField: UITextField = {
    let field = UITextField()
    
    field.autocapitalizationType = .none
    field.autocorrectionType = .no
    field.returnKeyType = .send
    field.layer.cornerRadius = 12
    field.layer.borderWidth = 1
    field.layer.borderColor = UIColor.lightGray.cgColor
    field.placeholder = "Password"
    field.leftView = UIView(frame: CGRect(x: 0,height: 0))
    field.leftViewMode = .always
    field.backgroundColor = .white
    field.isSecureTextEntry = true
    
    return field
} ()


private let loginButton: UIButton = {
   let button = UIButton()
    button.setTitle("Log In",for: .normal)
    button.backgroundColor = .link
    button.setTitleColor(.white,for: .normal)
    button.layer.cornerRadius = 12
    button.layer.masksToBounds = true
    button.titleLabel?.font = .systemFont(ofSize: 20,weight: .bold)
    return button
}()






override func viewDidLoad() {
    super.viewDidLoad()
    title = "Log In"
    view.backgroundColor = .white
    
    navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Register",style: .done,target: self,action: #selector(didTapRegister))
    
    loginButton.addTarget(self,action: #selector(loginButtonTapped),for: .touchUpInside)
    
    
    emailField.delegate = self
    passwordField.delegate = self
    
    // Add subviews
    view.addSubview(scrollView)
    scrollView.addSubview(logoView)
    scrollView.addSubview(emailField)
    scrollView.addSubview(passwordField)
    scrollView.addSubview(loginButton)

   
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    scrollView.frame = view.bounds
    
    let size = view.width/3
    logoView.frame = CGRect(x: (scrollView.width-size)/2,y: 20,width: size,height: size)
    emailField.frame = CGRect(x: 30,y: logoView.bottom+25,width: scrollView.width-60,height: 52)
    passwordField.frame = CGRect(x: 30,y: emailField.bottom+15,height: 52)
    loginButton.frame = CGRect(x: 30,y: passwordField.bottom+30,height: 52)
}


@objc private func loginButtonTapped() {
    
    emailField.resignFirstResponder()
    passwordField.resignFirstResponder()
    
    guard let email = emailField.text,let password = passwordField.text,!email.isEmpty,!password.isEmpty,password.count >= 6 else {
            alertUserLoginError()
            return
    }
    
    // Firebase Log In
    FirebaseAuth.Auth.auth().signIn(withEmail: email,password: password,completion: { [weak self] authResult,error in
        guard let strongSelf = self else {
            return
        }
        guard let result = authResult,error == nil else {
            print("Failed to log in with email: \(email)")
            
            return
        }
        let user = result.user
        print("Logged In user \(user)")
        strongSelf.navigationController?.dismiss(animated: true,completion: nil)
    })
    
}

func alertUserLoginError() {
    let alert = UIAlertController(title: "Woops",message: "Please enter all information to log in.",preferredStyle: .alert)
    
    alert.addAction(UIAlertAction(title: "Dismiss",style: .cancel,handler: nil))
    
    present(alert,animated: true)
}

func emailOrPasswordIncorrect() {
    let alert = UIAlertController(title: "Woops",message: "Incorrect email or password. Please retry.",animated: true)
}

@objc private func didTapRegister() {
    let vc = RegisterViewController()
    vc.title = "Create Account"
    navigationController?.pushViewController(vc,animated: true)
}

}

扩展名LoginViewController：UITextFieldDelegate {

func textFieldShouldReturn(_ textField: UITextField) -> Bool {
    
    if textField == emailField {
        passwordField.becomeFirstResponder()
    } else if textField == passwordField {
        loginButtonTapped()
    }
    
    return true
}

}

解决方法

如果“常规”选项卡中的“主界面”为空，则需要在appDelegate的didFinishLaunchingWithOptions函数中创建您自己的窗口，向其中添加根控制器，并使该窗口为keyAndVisible以查看您的控制器

AppDelegate.swift

 func application(_ application: UIApplication,didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        window = UIWindow(frame: UIScreen.main.bounds)
        window.rootViewController = LoginViewController()
        window.makeKeyAndVisible()
        return true
    }