Question

我在User类中有以下功能：

// Attempts to log in the user, given a password.
// Sets user's loginSuccessful to true upon successful login, false otherwise.
// If failed login, user's loginFailedMessage is also updated.
func attemptLogin(password:String) {
    // create a new NSURL pointing to the PHP login script
    let url = NSURL(string: loginScriptLocation)

    // create a new NSMutableURLRequest of type POST
    let request = NSMutableURLRequest(URL: url!)
    request.HTTPMethod = "POST"

    // add POST string with username and password to request
    let postString = "username=\(self.username)&password=\(password)"
    request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)

    // send the request and get the JSON results
    let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {
        data, response, error in
        // if there is an error with the request, print it
        if error != nil {
            println("error: \(error)")
            return
        }
        // otherwise, go ahead and parse JSON results
        var err:NSError?
        var json = NSJSONSerialization.JSONObjectWithData(data, options: .MutableContainers, error: &err) as? NSDictionary
        if let parseJSON = json {
            var resultValue = parseJSON["status"] as? String
            if resultValue! == "success" {
                // login successful
                self.loginSuccessful = true
            }
            else {
                // login not successful
                self.loginSuccessful = false
                self.loginFailedMessage = parseJSON["message"] as! String
            }
        }
    }
    task.resume()
}

问题是......

当触发我的登录UIButton的IBAction时，在我的LoginViewController中调用此attemptLogin（）函数。在此IBAction函数内调用attemptLogin（）之后，其后面的语句将检查用户的loginSuccessful变量是否已设置为true。如果为true，则意味着要转到不同的View Controller（将用户登录）;如果为false，则表示显示错误消息。

但是当然这不起作用，因为当我检查loginSuccessful是否已设置为true时（在我调用attemptLogin（）之后），我的NSURLSession还没有到达那一点。我觉得我需要在我的NSURLSession中添加一个“闭包”或“完成处理程序”，但即使在搜索StackOverflow之后我也真的不明白如何做到这一点。我是iOS编程和异步/同步方法的初学者，所以不要评判我！

如何修改现有的attemptLogin（）函数，以便在NSURLSession完成时触发某些事情（这样我可以在视图控制器中转到另一个屏幕，或者如果有的话，向用户显示警告误差）？

这是我的LoginViewController中的代码：

// Triggered when login button is tapped
// Attempts to log in a user with username and password typed in.
// Successful login -> takes user to Explore screen
// Failed login -> shows alert message with error
@IBAction func loginButtonTap(sender: UIButton) {
    if (usernameTextField.text.isEmpty || passwordTextField.text.isEmpty) {
        // show alert saying missing required field
    }
    else {
        // attempt login
        self.myUser.setUsernameWithoutPushingToDatabase(self.usernameTextField.text)
        self.myUser.attemptLogin(self.passwordTextField.text)
        if (self.myUser.didLoginSuccessfully()) {
            // login successful, segue to Explore screen
            self.performSegueWithIdentifier("loginToExploreSegue", sender: self)
        }
        else {
            // login failed, display alert with error message
            var incorrectPassAlert = UIAlertController(title: "Login Failed", message: self.myUser.loginFailedMessage, preferredStyle: UIAlertControllerStyle.Alert)
            incorrectPassAlert.addAction(UIAlertAction(title: "OK", style: .Default, handler: nil))
            self.presentViewController(incorrectPassAlert, animated: true, completion: nil)
        }
    }
}

Answer 1

您是对的，您希望将关闭传递给attemptLogin

尝试这样的事情

func attemptLogin(password:String, completion: (Bool) -> Void)

然后

if resultValue! == "success" {
    // login successful
    completion(true)
}
else {
    completion(false)
}

最后，您必须在loginButtonTap

中创建闭包

self.myUser.attemptLogin(self.passwordTextField.text, completion: (successful: Bool) -> Void) { 
   if successful {
        // login was good
   } else {
       // login was bad
   }
})

Answer 2

您的attemptLogin函数应该使用如下所示的完成处理程序：

func attemptLogin(password:String, completionHandler: (success: Bool, message: String) -> ()) { your code }

在该方法中，您应该将结果数据传递给该完成处理程序：

if resultValue! == "success" {
      // login successful
      self.loginSuccessful = true
      completionHandler(success: True, message: "Login Successful.")
}
else {
      // login not successful
      self.loginSuccessful = false
      self.loginFailedMessage = parseJSON["message"] as! String
      completionHandler(success: False, message: loginFailedMessage)
}

最后，您可以像这样调用attemptLogin：

self.myUser.attemptLogin(self.passwordTextField.text, {(success: Bool, message: String) -> () in
         if(success) {
        //do something
         }
         else {
        // do something or print message etc.
        }
    })

在Swift中向我的NSURLSession添加一个完成处理程序

2 个答案: