关于ios：通过代码呈现的另一个ViewController上存在AlertController

Present AlertController Over another ViewController presented via code

我通过空VC上的代码实例化Parse的库存UI登录屏幕。如果用户的电子邮件未验证，我想显示一个AlertController。因此，我通过代码创建的logInViewController呈现了alertController...。我理解AlertController不在窗口层次结构中的错误，但是我不确定如何解决。如果我关闭logInViewController但我不想这样做，则希望它在后台存在，它可以工作。使用Swift。

此答案未解决确切的问题：AlertController不在窗口层次结构中

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override func viewDidAppear(animated: Bool) {

super.viewDidAppear(animated)
if (PFUser.currentUser() == nil) {

//build logInVC in Code:
var logInViewController = PFLogInViewController()

var logInLogoTitle = UILabel()

logInLogoTitle.text ="Thredz"

logInLogoTitle.font = UIFont(name:"Cochin", size: 40.0)

logInViewController.fields = PFLogInFields.UsernameAndPassword | PFLogInFields.LogInButton | PFLogInFields.SignUpButton | PFLogInFields.PasswordForgotten | PFLogInFields.Twitter

logInViewController.logInView?.backgroundColor = UIColor.whiteColor()

logInViewController.logInView?.logo = logInLogoTitle

logInViewController.delegate = self

//present log in VC
self.presentViewController(logInViewController, animated: true, completion: nil)

//build signUpViewController
var signUpViewController = PFSignUpViewController()

signUpViewController.delegate = self

var signUpLogoTitle = UILabel()

signUpLogoTitle.text ="Thredz"

signUpViewController.signUpView?.logo = signUpLogoTitle

logInViewController.signUpController = signUpViewController

}

}

func logInViewController(logInController: PFLogInViewController, didLogInUser user: PFUser) {

if (PFTwitterUtils.isLinkedWithUser(user)) {
var twitterUsername = PFTwitterUtils.twitter()?.screenName

PFUser.currentUser()?.username = twitterUsername

PFUser.currentUser()?.saveEventually(nil)

}

if user["emailVerified"] as! Bool == true {
dispatch_async(dispatch_get_main_queue()) {
self.performSegueWithIdentifier(self.peopleTableViewControllerSegue, sender: nil)
}
} else {
// User needs to verify email address before continuing
let alertController = UIAlertController(
title:"Email address verification",
message:"We have sent you an email that contains a link - you must click this link before you can continue.",
preferredStyle: UIAlertControllerStyle.Alert
)
alertController.addAction(UIAlertAction(title:"OK",
style: UIAlertActionStyle.Default,
handler: nil)
)

self.presentViewController(alertController, animated: true, completion: nil)
}

}