how to get my UIWindow using UIApplication?

问题:

I have only one window and I tried

UIWindow* mWindow = [[UIApplication sharedApplication] keyWindow];

but this returned nil.

I also tried:

UIWindow* mWindow = (UIWindow*)[[UIApplication sharedApplication].windows objectAtIndex:0];

But this raised an exception and the app closed, when I tried to print out

[[UIApplication sharedApplication].windows count]

It printed 0

Note: I am putting this in my only view controller's viewDidLoad method and this is completely a new iPad View Based Application so I changed nothing, just trying to get the window

Please help me to get this object

回答1:

If your main window is an outlet of your AppDelegate (which should be the case), you may simply use

MyAppDelegate* myDelegate = (((MyAppDelegate*) [UIApplication sharedApplication].delegate));
[myDelegate.window ...]

回答2:

Easiest way is to get the window from the app delegate instead:

UIWindow *keyWindow = [[[UIApplication sharedApplication] delegate] window];
// Do something with the window now

回答3:

Your application's key window isn't set until [window makeKeyAndVisible] gets called in your app delegate. Your UIViewController is probably being loaded from a NIB before this call. This explains why keyWindow is returning nil.

Luckily, your view controller doesn't need to go through UIApplication to get the window. You can just do:

UIWindow *mWindow = self.view.window;

回答4:

[[[UIApplication sharedApplication] windows] objectAtIndex:0]; // You can also check the count of this to make sure, because if there are no windows it will crash.