ios - 为什么程序在登录时不执行segue？

Question

我有一个登录屏幕，如果单击登录按钮时凭据正确，则将执行 segue。 Segue 具有正确的标识符，并且用户已登录，因为我通过 currentUser 传递数据，并且它显示在控制台中，指示用户已登录，但 Segue 未执行。为什么？下面是我的登录代码。

 @IBAction func loginAction(sender: AnyObject) {

    let username = self.usernameField.text
    let password = self.passwordField.text


    if(username!.utf16.count) < 4 || (password!.utf16.count < 5){

    let alert = UIAlertView(title: "Invalid", message: "Username must be greater then 4 and Password must be greater then 5", delegate: self, cancelButtonTitle: "OK")
    alert.show()

    }else{

        self.actInd.startAnimating()

        PFUser.logInWithUsernameInBackground(username!, password: password!, block: { (user, error) -> Void in

            self.actInd.stopAnimating()

            if ((user) != nil) {

                var alert = UIAlertView(title: "Success", message: "Logged In", delegate: self, cancelButtonTitle: "OK")
                alert.show()

                self.performSegueWithIdentifier("login", sender: self)

            }else {

                let alert = UIAlertView(title: "Error", message: "\(error)", delegate: self, cancelButtonTitle: "OK")
                alert.show()

            }



        })

    }


}

Answer 1

您正在后台线程上调用performSegueWithIdentifier。尝试用

包裹它

dispatch_async(dispatch_get_main_queue(),{



 })