Ios 如何在swift 3中显示特定服务器状态代码的警报？

我开发了一个应用程序，允许用户登录到服务器，并且运行良好。 现在，我想显示一个错误警报，当服务器返回statusCode:500时，该警报表示出现了问题。 此外，我还想阻止segue，使其停留在登录屏幕上，直到用户输入正确的凭据

这是我的班级：

    import Alamofire //A framework for handling http requests nicely
    import UIKit 

 //A class which will do the login process
  class InitialViewController: UIViewController {

//Variables for the URL, parameters, authentication token and alertView
let url = "https://api.sis.kemoke.net/auth/login"
var parameters = ["email": "", "password": ""]
var token = ["X-Auth-Token": ""]

// Parameters textfields
@IBOutlet weak var email: UITextField?
@IBOutlet weak var password: UITextField?

// A method for the login button
@IBAction func loginButton(_ sender: UIButton) {
    parameters["email"] = email?.text //Read email from text field
    parameters["password"] = password?.text //Read password from text field
    Alamofire.request(url, method: .post, parameters: parameters, encoding: URLEncoding.httpBody, headers: token).responseJSON {
        (response) in
        print(response.result.value as Any)
        //Reading JWT authentication token from the server
                    if let tokenString = response.result.value as? String {
            self.token["X-Auth-Token"] = tokenString
        }
        //Check if the server returned nil
        if response == nil {
        let alert = UIAlertController(title: "Alert", message: "Message", preferredStyle: UIAlertControllerStyle.alert)
         alert.addAction(UIAlertAction(title: "Click", style: UIAlertActionStyle.default, handler: nil))
         self.present(alert, animated: true, completion: nil)
        }


        //Show the error message

        //Check NSUserData if the user is already logged in
    }
}
//ViewDidLoad method used to preconfigure the first view
override func viewDidLoad() {
    super.viewDidLoad()
}
 }

如果您能提供演示，我可以帮助您提供简洁的备选答案 成功登录尝试的响应

在您的登录按钮方法中替换此代码：

@IBAction func loginButton(_ sender: UIButton) {
    parameters["email"] = email?.text //Read email from text field
    parameters["password"] = password?.text //Read password from text field
    Alamofire.request(url, method: .post, parameters: parameters, encoding: URLEncoding.httpBody, headers: token).responseJSON {
        (response) in

        //Reading JWT authentication token from the server
        if let tokenString = response.result.value as? String {
            self.token["X-Auth-Token"] = tokenString
        }

        //Check if the server returned nil
        let responseObject = response.result.value as! Dictionary<String, Any>
        let statusCode = responseObject["statusCode"] as! Int
        print("Status Code \(statusCode)")

        // manage alerts for different status codes
        if statusCode == 500 {
            // present alert
            let alert = UIAlertController(title: "Alert", message: "Message", preferredStyle: UIAlertControllerStyle.alert)
            alert.addAction(UIAlertAction(title: "Click", style: UIAlertActionStyle.default, handler: nil))
            self.present(alert, animated: true, completion: nil)
        } else if  statusCode == 200 {
            // 200 status code for successful login
            // code to navigate to other screen
            // depends on what reponse you are getting on successful login attempt
        }
    }
}

@iAction func登录按钮（uu发件人：ui按钮）{
参数[“电子邮件”]=电子邮件？.text//从文本字段读取电子邮件
参数[“密码”]=密码？.text//从文本字段读取密码
请求（url，方法：.post，参数：参数，编码：URLEncoding.httpBody，头：令牌）。responseJSON{
（答复）在
//从服务器读取JWT身份验证令牌
如果让tokenString=response.result.value作为？字符串{
self.token[“X-Auth-token”]=tokenString
}
//检查服务器是否返回nil
让responseObject=response.result.value为！字典
将statusCode=responseObject[“statusCode”]设为！Int
打印（“状态代码\（状态代码）”）
//管理不同状态代码的警报
如果statusCode==500{
//当前警报
let alert=UIAlertController（标题：“警报”，消息：“消息”，首选样式：UIAlertControllerStyle.alert）
addAction（UIAlertAction（标题：“单击”，样式：UIAlertActionStyle.default，处理程序：nil））
self.present（警报、动画：true、完成：nil）
}如果statusCode==200，则为else{
//200成功登录的状态代码
//导航到其他屏幕的代码
//取决于您在成功登录尝试时得到的响应
}
}
}

有明确的错误说明