UIViewController.View.Window is null in ViewDidLoad method

问题

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)

回答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.

回答2:

Instead of self.view.window use

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

回答3:

you can call it like:- 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
    }

来源：https://stackoverflow.com/questions/10278204/uiviewcontroller-view-window-is-null-in-viewdidload-method