ios - 以编程方式转换 View Controller 时出错

Question

我正在使用此代码在用户登录后转换 View Controller :

let controller = self.storyboard?.instantiateViewControllerWithIdentifier("messagesVC") as! messagesViewController
self.presentViewController(controller, animated: true, completion: nil)

当我在编辑器中时，代码不会引发任何错误，但是当它运行时什么也没有发生，我返回此错误:

2015-11-19 12:06:08.835 collaboration[8788:70890] Warning: Attempt to present on which is already presenting

View Controller “messagesViewController”存在，它的 Storyboard场景具有标识符“messagesVC”。我不知道哪里出了问题......如果你知道请帮帮我。
谢谢

登录按钮:

@IBAction func loginButton(sender: UIButton) {
        let savedUsername = NSUserDefaults.standardUserDefaults().stringForKey("username")! as String
        if savedUsername == "" {
        if usernameInput.text != "" && passwordInput.text != "" {
            let usernameTextFieldString = usernameInput.text! as String
            let passwordTextFieldString = passwordInput.text! as String
            let myUrl = NSURL(string: "http://127.0.0.1/bubble/login.php?username=\(usernameTextFieldString)&password=\(passwordTextFieldString)&secretKey=kjdfb4u7bksSDDF44wlksdnw33j4")
            let request = NSMutableURLRequest(URL: myUrl!)
            request.HTTPMethod = "POST"
            let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {
                data, response, error in
                dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) {
                    let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
                    if error != nil {
                        print("Error: \(error)")
                    }
                    dispatch_async(dispatch_get_main_queue()) {
                        let userInfo = responseString!.componentsSeparatedByString("9254203598")
                        let userInfoCount = userInfo.count
                        if userInfoCount == 4 {
                            let userInfoId = userInfo[1] as String
                            let userInfoUsername = userInfo[2] as String
                            let userInfoPassword = userInfo[3] as String
                            NSUserDefaults.standardUserDefaults().setObject(userInfoId, forKey: "id")
                            NSUserDefaults.standardUserDefaults().setObject(userInfoUsername, forKey: "username")
                            NSUserDefaults.standardUserDefaults().setObject(userInfoPassword, forKey: "password")
                            NSUserDefaults.standardUserDefaults().synchronize()
                            let keyId = NSUserDefaults.standardUserDefaults().stringForKey("id")
                            let keyUsername = NSUserDefaults.standardUserDefaults().stringForKey("username")
                            let keyPassword = NSUserDefaults.standardUserDefaults().stringForKey("password")
                            if keyId != nil && keyUsername != nil && keyPassword != nil {
                                self.sendAlert("Success", message: "You have been logged in successfully")
                                self.usernameInput.text = ""
                                self.passwordInput.text = ""
                                self.loginStatus()
                    //VIEW CONTROLLER TRANSITION TO FIX
                                let controller = self.storyboard?.instantiateViewControllerWithIdentifier("messagesVC") as! messagesViewController
                                self.presentViewController(controller, animated: true, completion: nil)
                            }
                        } else {
                            self.sendAlert("Error", message: "Unable to login")
                        }
                    }
                }
            }
            task.resume()
            loginStatus()
        } else {
            sendAlert("Login Invalid", message: "The username and password you entered are not associated with an account")
        }
        } else {
            self.sendAlert("Error", message: "You must be logged in to log out")
        }
    }

修改后的代码:

@IBAction func loginButton(sender: UIButton) {
        let savedUsername = NSUserDefaults.standardUserDefaults().stringForKey("username")! as String
        if savedUsername == "" {
        if usernameInput.text != "" && passwordInput.text != "" {
            let usernameTextFieldString = usernameInput.text! as String
            let passwordTextFieldString = passwordInput.text! as String
            let myUrl = NSURL(string: "http://127.0.0.1/bubble/login.php?username=\(usernameTextFieldString)&password=\(passwordTextFieldString)&secretKey=kjdfb4u7bksSDDF44wlksdnw33j4")
            let request = NSMutableURLRequest(URL: myUrl!)
            request.HTTPMethod = "POST"
            let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {
                data, response, error in
                dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) {
                    let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
                    if error != nil {
                        print("Error: \(error)")
                    }
                    dispatch_async(dispatch_get_main_queue()) {
                        print(responseString)
                        let userInfo = responseString!.componentsSeparatedByString("9254203598")
                        let userInfoCount = userInfo.count
                        if userInfoCount == 4 {
                            let userInfoId = userInfo[1] as String
                            let userInfoUsername = userInfo[2] as String
                            let userInfoPassword = userInfo[3] as String
                            NSUserDefaults.standardUserDefaults().setObject(userInfoId, forKey: "id")
                            NSUserDefaults.standardUserDefaults().setObject(userInfoUsername, forKey: "username")
                            NSUserDefaults.standardUserDefaults().setObject(userInfoPassword, forKey: "password")
                            NSUserDefaults.standardUserDefaults().synchronize()
                            let keyId = NSUserDefaults.standardUserDefaults().stringForKey("id")
                            let keyUsername = NSUserDefaults.standardUserDefaults().stringForKey("username")
                            let keyPassword = NSUserDefaults.standardUserDefaults().stringForKey("password")
                            if keyId != nil && keyUsername != nil && keyPassword != nil {
                                self.sendAlert("Success", message: "You have been logged in successfully")
                                self.usernameInput.text = ""
                                self.passwordInput.text = ""
                                NSUserDefaults.standardUserDefaults().stringForKey("username")
                                //self.loginStatus()
                                //VIEW CONTROLLER TRANSITION TO FIX
                                let controller = self.storyboard?.instantiateViewControllerWithIdentifier("messagesVC") as! messagesViewController
                                self.presentViewController(controller, animated: true, completion: nil)
                            }
                        } else {
                            print("Unable to login")
                            //self.sendAlert("Error", message: "Unable to login")
                        }
                    }
                }
            }
            task.resume()
            //loginStatus()
        } else {
            //sendAlert("Login Invalid", message: "The username and password you entered are not associated with an account")
        }
        } else {
            //sendAlert("Error", message: "You must be logged in to log out")
        }
    }

Answer 1

我看到两件事可能是罪魁祸首:

您正在调用 self.sendAlert，我假设它会在显示您的 messagesVC Controller 之前在当前 View Controller 上显示一个 UIAlertController。这是在主线程上连续发生的，看起来您在显示警报时正在显示消息 Controller 。为什么不等到消息 View Controller 加载后才显示警报，或者将 View Controller 作为警报 Controller 上的 UIAlertAction 呈现？

其次，您正在调用函数 self.loginStatus()。如果您在该函数中显示警报或任何其他 View Controller ，那也可能是您的问题。