swift - 验证按钮单击并更改 Controller View iOS

Question

我是 Swift iOS 开发新手，我正在创建一个用户登录页面，当他们单击登录按钮时，会对用户输入执行一些验证，如果成功，将用户发送到新页面。在 Storyboard中，我有两个 View Controller ，登录页面和登录成功后的页面。我已经创建了从登录页面上的登录按钮到第二页的segue。这是以下代码。

@IBAction func loginAction(_ sender: Any) {
    guard let username = usernameField.text, let password = passwordField.text else {
        return
    }
    if (username.isEmpty && password.isEmpty) {
        displayAlert(message: "username and password are not set")
        return
    }
    if (username.isEmpty) {
        displayAlert(message: "username is not set")
        return
    }
    if (password.isEmpty) {
        displayAlert(message: "password is not set")
        return
    }
}

此代码有效，并在登录后成功将用户发送到正确的页面。但是，当我添加显示“成功”的警报时，警报启动后不会加载新页面。关闭。以下是添加登录成功警报的代码。该代码添加在函数 loginAction 中的最终条件之后。

let alert = UIAlertController(title: "Success", message: "Sucessfully logged in", preferredStyle: UIAlertControllerStyle.alert)
alert.addAction(UIAlertAction(title: "Done", style: UIAlertActionStyle.default, handler: nil))
self.present(alert, animated: true, completion: nil)

为什么我没有被发送到带有此警报的新页面？如果“成功”警报被注释掉，我将被发送到正确的页面。

我使用的是 Xcode 9 和 Swift 4。

编辑:这是代码的类。

class ViewController: UIViewController {
    @IBOutlet weak var usernameField: UITextField!
    @IBOutlet weak var passwordField: UITextField!

    @IBAction func loginAction(_ sender: Any) {
        guard let username = usernameField.text, let password = passwordField.text else {
            return
        }
        if (username.isEmpty && password.isEmpty) {
            displayAlert(message: "username and password are not set")
            return
        }
        if (username.isEmpty) {
            displayAlert(message: "username is not set")
            return
        }
        if (password.isEmpty) {
            displayAlert(message: "password is not set")
            return
        }
        login(info: username)
        // self.present(alert, animated: true, completion: nil)
        // self.present(self, animated: true) {
        //     let alert = UIAlertController(title: "Success", message: "Sucessfully logged in with \(username)", preferredStyle: UIAlertControllerStyle.alert)
        //     alert.addAction(UIAlertAction(title: "Done", style: UIAlertActionStyle.default, handler: nil))
        //     self.present(alert, animated: true, completion: nil)
        // }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

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

    private func login(info: String) {
        let alert = UIAlertController(title: "Success", message: "Sucessfully logged in with \(info)", preferredStyle: UIAlertControllerStyle.alert)
        // alert.addAction(UIAlertAction(title: "Done", style: UIAlertActionStyle.default) { action in self.dismiss(animated: true) })
        alert.addAction(UIAlertAction(title: "Done", style: UIAlertActionStyle.default, handler: nil))
        self.present(alert, animated: true, completion: nil)
    }

    private func displayAlert(message: String) {
        let alert = UIAlertController(title: "Alert", message: message, preferredStyle: UIAlertControllerStyle.alert)
        alert.addAction(UIAlertAction(title: "Ok", style: UIAlertActionStyle.default, handler: nil))
        self.present(alert, animated: true, completion: nil)
    }
}

Answer 1

为了让它正常工作，我需要这样做。我更新了我的函数 loginAction。

let alert = UIAlertController(title: "Success", message: "Sucessfully logged in with \(info)", preferredStyle: UIAlertControllerStyle.alert)
alert.addAction(UIAlertAction(title: "Done", style: UIAlertActionStyle.default) { action in
    self.performSegue(withIdentifier: "loginSegue", sender: nil)
})
self.present(alert, animated: true, completion: nil)