UIViewController.View.Window is null in ViewDidLoa

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:

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
}