ios - 应该使用标识符执行 segue - 错误

Question

我正在使用shouldPerformSegueWithIdentifier方法控制何时执行segue。

  override func shouldPerformSegueWithIdentifier(identifier: String!, sender: AnyObject?) -> Bool {

    if identifier == "login" {
        if loginSuccess != true {

            var alert = UIAlertController(title: "Alert", message: "Please enter correct login details", preferredStyle: UIAlertControllerStyle.Alert)
            alert.addAction(UIAlertAction(title: "Ok", style: UIAlertActionStyle.Default, handler: nil))
            self.presentViewController(alert, animated: true, completion: nil)

            return false
        }
    }

    return true
}

我在类的开头声明了 loginSuccess 变量，如下所示:

   var loginSuccess:Bool? 

当 API 通过以下方式成功验证用户登录详细信息时，我将此 bool 变量更改为 true:

  self.loginSuccess = true

以上行位于 if 语句之后，用于检查 API 返回的 JSON 是否不为空。

我的问题是，当我运行代码并在应用程序中输入登录详细信息并单击登录按钮时，它总是第一次拒绝登录详细信息，当我单击登录按钮时第二次执行segue。无论我的登录详细信息是否完美，第一次点击总是被拒绝，第二次点击被接受，segue 被处理。

我认为当它第一次运行 segue 代码时，它会将“loginSuccess”的初始值视为 false，这就是它拒绝它的原因。

我该如何解决这个问题。它与 bool 变量有关。

完整代码:

 import UIKit

 class ViewController: UIViewController {

 var loginSuccess:Bool?

@IBOutlet weak var password: UITextField!
@IBOutlet weak var emailAdd: UITextField!


@IBAction func loginUser(sender: AnyObject) {

    var x:String = password.text
    var y:String = emailAdd.text

    var request = NSMutableURLRequest(URL: NSURL(string: "http://myAPIlink.com/login")!)
    var session = NSURLSession.sharedSession()
    request.HTTPMethod = "POST"

    var params = ["email":"\(y)", "password":"\(x)"] as Dictionary<String, String>

    var err: NSError?
    request.HTTPBody = NSJSONSerialization.dataWithJSONObject(params, options: nil, error: &err)
    request.addValue("application/json", forHTTPHeaderField: "Content-Type")
    request.addValue("application/json", forHTTPHeaderField: "Accept")

    var task = session.dataTaskWithRequest(request, completionHandler: {data, response, error -> Void in
        println("Response: \(response)")
        var strData = NSString(data: data, encoding: NSUTF8StringEncoding)
        println("Body: \(strData)")
        var err: NSError?
        var json = NSJSONSerialization.JSONObjectWithData(data, options: .MutableLeaves, error: &err) as? NSDictionary

        // Did the JSONObjectWithData constructor return an error? If so, log the error to the console
        if(err != nil) {

            println(err!.localizedDescription)
            let jsonStr = NSString(data: data, encoding: NSUTF8StringEncoding)
            println("Error could not parse JSON: '\(jsonStr)'")

        }
        else {

            // The JSONObjectWithData constructor didn't return an error. But, we should still
            // check and make sure that json has a value using optional binding.

            if let parseJSON = json {

                // CHANGE THE loginSuccess Boolean HERE
                    self.loginSuccess = true

                // Okay, the parsedJSON is here, let's get the value for 'success' out of it

                var fullname = parseJSON["fullname"] as! String
                println("Succes: \(fullname)")

                var region = parseJSON["region"] as! String
                println("Region: \(region)")

                var uTarget = parseJSON["target"] as! String
                println("Target: \(uTarget)")


            }
            else {
                // Woa, okay the json object was nil, something went worng. Maybe the server isn't running?
                let jsonStr = NSString(data: data, encoding: NSUTF8StringEncoding)
                println("Error could not parse JSON: \(jsonStr)")

            }
        }
    })

    task.resume()
}
override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    self.view.backgroundColor = UIColor(patternImage: UIImage(named: "podcastbg.jpg")!)

}

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



override func shouldPerformSegueWithIdentifier(identifier: String!, sender: AnyObject?) -> Bool {

    if identifier == "login" {
        if loginSuccess != true {

            var alert = UIAlertController(title: "Alert", message: "Please enter correct login details", preferredStyle: UIAlertControllerStyle.Alert)
            alert.addAction(UIAlertAction(title: "Ok", style: UIAlertActionStyle.Default, handler: nil))
            self.presentViewController(alert, animated: true, completion: nil)

            return false
        }
    }

    return true
}
}

如果您需要更多信息来回答问题，请告诉我。提前致谢。

Answer 1

我会稍微改变一下你的代码:

1. 用户应输入用户名和密码
2. 对您的服务进行(异步)调用(向用户显示旋转图标)
3. 如果结果有效 -> 更改 segue

我不会使用

shouldPerformSegueWithIdentifier

只是:

  if let parseJSON = json {

            // CHANGE THE loginSuccess Boolean HERE

            self.performSegueWithIdentifier("loginSuccessSegue", sender: nil)

或者以其他方式向用户显示错误消息。

如果您愿意，可以设置“登录成功”值，然后使用

进行检查

   prepareForSegue