UIKeyboardTaskQueue may only be called from the main thread

问题

I have a problem while trying to make a function that automatically create POST request, send them, get the response, and handle them then show UIAlertView to tell the user which problem it is.

Here is my code :

let task = session.dataTaskWithRequest(request, completionHandler:{ (data, response, error) -> Void in

    dispatch_async(dispatch_get_main_queue(),{
        var alert = UIAlertController(title: "Chargement", message: "Envoi des informations...", preferredStyle: UIAlertControllerStyle.Alert)
        viewController.presentViewController(alert, animated: true, completion: nil)


        answer = NSString(data: data!, encoding: NSUTF8StringEncoding)!
        print(answer)
    var complete = false
    alert.dismissViewControllerAnimated(true, completion: { () -> Void in
        complete = true
    })

    while(!complete)
    {

    }
    var textmsg: String
    if(answer == "#400")
    {
        textmsg = "Il manque une information !"
    }
    else if(answer == "#50")
    {
        textmsg = "Le compte fourni ne correspond pas."
    }
    else if(answer == "#100")
    {
        textmsg = "Impossible d'identifier l'application."
    }
    else if(answer == "#1")
    {
        textmsg = "Transfert terminé avec succès !"
    }
    else {
        textmsg = "Echec du transfert."
    }
    let alertComplete = UIAlertController(title: "Chargement", message: textmsg, preferredStyle: UIAlertControllerStyle.Alert)
    alertComplete.addAction(UIAlertAction(title: "Ok", style: UIAlertActionStyle.Default, handler: nil))
    viewController.presentViewController(alertComplete, animated: true, completion: nil)
    })
})

task.resume();

The error code is the following :

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[UIKeyboardTaskQueue waitUntilAllTasksAreFinished] may only be called from the main thread.'

When my request return a bad response (the #400, #50, #100), the code works and show the UIAlertView but if the response is good, it gives me the error code as above.

回答1:

You should call your UIAlertController on the main thread because you're dealing with the ui.

Swift 2.X

dispatch_async(dispatch_get_main_queue(),{ 
               var alert = UIAlertController(title: "Chargement", message: "Envoi des informations...", preferredStyle: UIAlertControllerStyle.Alert)
                viewController.presentViewController(alert, animated: true, completion: nil)

                answer = NSString(data: data!, encoding: NSUTF8StringEncoding)!
                print(answer)
             var complete = false
    alert.dismissViewControllerAnimated(true, completion: { () -> Void in
        complete = true
    })
    while(!complete)
    {

    }
}

Swift 4.2

DispatchQueue.main.async {
    var alert = UIAlertController(title: "Chargement", message: "Envoi des informations...", preferredStyle: UIAlertControllerStyle.Alert)
    viewController.presentViewController(alert, animated: true, completion: nil)

    let answer = String(data: data!, encoding: .utf8)!
    print(answer)
    var complete = false
    alert.dismissViewControllerAnimated(true, completion: { () -> Void in
        complete = true
    })
    while(!complete)
    {

    }
}

回答2:

For swift 3.x and 4.x

DispatchQueue.main.async(execute: {
// work Needs to be done
 })

来源：https://stackoverflow.com/questions/39559751/uikeyboardtaskqueue-may-only-be-called-from-the-main-thread