UIViewController.View.Window is null in ViewDidLoad method

Question

Regardless on which controller type (UIViewController, UITableViewController), the following line always yields null in the ViewDidLoad method:

this.View.Window

Is this behavior normal, or am I doing something odd? What could lead to UIViewController.View.Window being null?

(I suppose this question concerns not only MonoTouch, but also 'normal' Objective-C Cocoa).

(MonoTouch 5.2.11, Xcode 4.2.1 4D502)

Seigneury

Answer 1

According to the documentation of UIView, the window property is nil if the view has not yet been added to a window which is the case when viewDidLoad is called.

Celik

What method is called after the view is added to a window? – Viceroy

@AlexRyan You can use -viewDidAppear. – Suneya

Answer 2

self.view.window will be available in viewDidAppear:

override func viewDidAppear(_ animated: Bool) {
    print(self.view.window)
    let vc = self.storyboard?.instantiateViewController(identifier: "SecondViewController") as? SecondViewController
    self.view.window?.rootViewController = vc
}

Ables

Answer 3

Instead of self.view.window use

[(YourAppDelegate *)[[UIApplication sharedApplication] delegate] window]

Practical

It's a problem if you are using UIScene. – Weariful

Answer 4

If using UIScene you can get the window from viewWillAppear like this:

    func windowByParent(vc: UIViewController) -> UIWindow? {
        var window: UIWindow? = nil
        var parent: UIViewController? = vc
        
        while parent != nil && window == nil {
            window = parent?.view.window
            parent = parent?.parent
        }
        return window
    }

Wally