How to present a view controller while performing background tasks? - multithreading

Question

I am using Parse.com and swift
I have an initial view controller that presents the parse.com login.
Once the login is complete and the objects are saved in the background I want to present my navigation controller's root view controller (first controller linked in the storyboard).
How is this done with all the asynchronous calls?
This is what I have but it jumps back to the login screen and doesn't
func signUpViewController(signUpController: PFSignUpViewController!, didSignUpUser user: PFUser!) {
currentUser = user as? User
currentUser!.isManager = false
var query = PFUser.query()
query.findObjectsInBackgroundWithBlock { (objects: [AnyObject]!, error: NSError!) -> Void in
if objects.count == 1 {
currentUser!.isManager = true
}
currentUser?.saveInBackgroundWithBlock({ (success: Bool, error: NSError!) -> Void in
if success == false || error != nil {
println(error)
} else {
currentCompany = Company()
currentCompany!.companyName = "My Company"
currentCompany!.saveInBackgroundWithBlock({ (success: Bool!, error: NSError!) -> Void in
if success == false {
println(error)
}
})
}
})
}
dismissViewControllerAnimated(true, completion: { () -> Void in
self.performSegueWithIdentifier("jumpFromInitialToMessages", sender: self)
// let vc = MessagesViewController()
// self.navigationController?.presentViewController(vc, animated: true, completion: nil)
})
}

Answer 1

If you want to initiate a UI transition/update inside the completion handler, you should insert a dispatch back to the main queue inside the completion handler closure:
var query = PFUser.query()
query.findObjectsInBackgroundWithBlock { (objects: [AnyObject]!, error: NSError!) -> Void in
// do something
// when done, do some UI update, e.g. perform segue to another scene
dispatch_async(dispatch_get_main_queue()) {
self.performSegueWithIdentifier("identifier", sender: self)
}
}
This is an example with a simple query, but the idea works with any asynchronously called completion handler closure: Just dispatch the UI update back to the main queue from within the closure.