Swift Attempt to present UIAlertController whose view is not in the window hierarchy (presented after TWTRShareEmailViewController)

Question

I'm using the Twitter login in the signup process of my app. And I'm asking for the user's email. Once I get it, I'd like to present a UIAlertController.

Here's my code:

func askForTWMail(){
    if (Twitter.sharedInstance().session() != nil) {
        let shareMailVC=TWTRShareEmailViewController(completion: {(mail:String!, error:NSError!) in
            if (mail != nil) {
                print("GOT MAIL: \(mail)")
                self.gotMail()
            }else{
                print("MAIL VC ERROR: \(error)")
            }
        })
        println("PRESENT MAIL VC")
        self.presentViewController(shareMailVC, animated: true, completion: nil)
    }else{
        println("User not logged in")
    }
}

func gotMail(){
    var alertController=UIAlertController(title: "Some title", message: "Some message", preferredStyle: UIAlertControllerStyle.Alert)
    var okAction=UIAlertAction(title:"Yes", style: UIAlertActionStyle.Default) {
    UIAlertAction in
    //some action
    }
    var cancelAction=UIAlertAction(title:"No", style: UIAlertActionStyle.Cancel){
    UIAlertAction in
    //some action
    }
    alertController.addAction(okAction)
    alertController.addAction(cancelAction)
    self.presentViewController(alertController, animated: true, completion: nil)                
}

But I get this error (I guess because the TWTRShareEmailViewController is not dismissed):

Warning: Attempt to present UIALertController on xViewController whose view is not in the window hierarchy!

Any idea of how I should write this? How can I know when the TWTRShareEmailViewController is dismissed to continue the signup process and be able to present my UIAlertController? I'm not aware of a delegate method related to TWTRShareEmailViewController.

Any help is appreciated. Thanks.

Answer 1

Found a solution here. I'm probably doing it wrong but if not it might be an Apple bug. The workaround is to delay the presentation of the UIAlertController:

dispatch_async(dispatch_get_main_queue(), ^{
    self.presentViewController(alertController, animated: true, completion: nil)
})

EDIT: I found another workaround (I don't use the solution I put down here anymore). I had to change this because the Twitter login was also breaking my transitions between VCs.

I now call a specific UIViewController (I called it something like TWLoginVC) where I do all the Twitter login and other stuff. The view is just black so the user don't see the process is actually done in another VC (he just has to pick up the Twitter user he wants to login with). I guess you could also put a clear background to be even more invisible.

When I call this view controller and dismiss it, the transition is not applied to it and I don't have any more problem with it.

---

EDIT Update for Swift:

DispatchQueue.main.async{
     self.present(alertController, animated: true, completion: nil)
}

Answer 2

Here's an updated answer for Swift 3 tested on Xcode 8 based on Marie Dm's answer.

DispatchQueue.main.sync {
     self.present(alertController, animated: true, completion: nil)
}