Why window is nil in AppDelegate

Question

I need to present view controller from the AppDelegate, so I wrote the following code:

let storyboard = UIStoryboard(name: "Main", bundle: nil)
let authViewController = storyboard.instantiateViewControllerWithIdentifier("ViewController") as ViewController
if let keyWindow = UIApplication.sharedApplication().keyWindow {
    keyWindow.rootViewController = authViewController
}

Unfortunately, window and keyWindow are both nil. Why?

Answer 1

You need to create the window yourself in AppDelegate if not using the main interface option:

self.window = UIWindow(frame:UIScreen.mainScreen().bounds) 

Swift 3.0+

self.window = UIWindow(frame: UIScreen.main.bounds) 

Then call your code above, using window.

Finally, call makeKeyAndVisible() on the window.