Parse Facebook User logged in, perform segue - ios

Question

I am trying to skip over my login view once a user is logged in. How can I check to see if a user is logged in through Facebook while the app is starting?
I currently have the following code in a LoginViewController:
override func viewWillAppear(animated: Bool) {
var loggedIn = PFFacebookUtils.session().isOpen;
if (loggedIn) {
performSegueWithIdentifier("skipLogin", sender: self)
}
}
This does not move to my next view even after the user has clicked the "Log in with Facebook" button.
I get the following error:
Warning: Attempt to persent <_Project.HomeViewController: 0x7fa331d3af00> on
<_Project.LoginViewController: 0x7fa331f08950> whose view is not in the window hierarchy!

Answer 1

As discussed in chat, you have basically two options here:
Let the user "see" the animation from the login view controller to the second one. In that case you should do the push in viewDidAppear instead of viewWillAppear (where the view is not fully prepared, as the runtime warning clearly states).
If you prefer showing the final view controller immediately, without any animation, then it's better to put that logic inside your app delegate, and choose which initial view controller should be loaded from here. In that case, you're not actually performing any segue, you're just assigning one or another view controller to the main window (or your navigation controller).
Parse has the "AnyWall" sample app that implements the second logic. See here for more details: https://parse.com/tutorials/anywall#2-user-management. In particular, the chapter 2.4 is of special interest, as it explains how you can keep a user logged-in.
Simply put, here's how they did it (I've adapted their Objective-C code to Swift):
func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
...
navigationController = UINavigationController()
...
// If we have a cached user, we'll get it back here
if PFFacebookUtils.session().isOpen {
// A user was cached, so skip straight to the main view
presentWallViewController(animated: false)
} else {
// No cached user, go to the welcome screen and
// have them log in or create an account.
presentLoginViewController(animated: true)
}
...
window = UIWindow(frame: UIScreen.mainScreen().bounds)
window.rootViewController = navigationController
window.makeKeyAndVisible()
return true
}
In each of the two methods present...ViewController, they use the following skeleton:
func presentxxxViewController(#animated: Bool) {
NSLog("Presenting xxx view controller")
// Go to the welcome screen and have them log in or create an account.
let storyboard = UIStoryboard(name: "Main", bundle: nil) // Here you need to replace "Main" by the name of your storyboard as defined in interface designer
let viewController = storyboard.instantiateViewControllerWithIdentifier("xxx") as xxxViewController // Same here, replace "xxx" by the exact name of the view controller as defined in interface designer
//viewController.delegate = self
navigationController?.setViewControllers([viewController], animated: animated)
}
The navigationController and window vars should be defined like this in AppDelegate:
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
var navigationController: UINavigationController?
...
}
If your app also uses a navigation controller as its root view controller, you can probably use the same code.