How do I get the keyWindow reference in a swift app?

Question

In Objective-C in the viewDidLoad method of a UIViewController I do this to get the keyWindow reference in my iOS app:

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

So, I am porting this view controller into Swift and I do this one the viewDidLoad call:

let window = UIApplication.sharedApplication().keyWindow

I am trying to understand why the window is nil. When I put a breakpoint right after that line I then inspect window in the console and I get this:

(lldb) po window nil

How can I get window to be a valid reference to the keyWindow of my application in swift?

let window: UIWindow? = UIApplication.sharedApplication().windows[0] as? UIWindow might present what you look for... or since func viewDidAppear(_ animated: Bool) (until your view is visible!) you have direct access to the window via self.view.window, maybe that is what you look for... — holex
– holex, Commented Jun 8, 2015 at 15:11

superarts.org · Accepted Answer · 2023-12-27 00:15:35Z

42

I came to this question when I was searching for getting window in swift. If you want to get window instead of keyWindow, try this (Swift 2):

if let appDelegate = UIApplication.sharedApplication().delegate as? AppDelegate, let window = delegate.window { MBProgressHUD.show(text, view:window) }

Updated for Swift 3: (Thanks @Trevor)

if let appDelegate = UIApplication.shared.delegate as? AppDelegate, let window = delegate.window { MBProgressHUD.show(text, view:window) }

edited Dec 27, 2023 at 0:15

answered Jun 8, 2015 at 15:05

superarts.org

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4 Comments

allenlinli Over a year ago

But window.keyWindow will be false?! let windowFirst = NSApp.windows.first print(windowFirst!.keyWindow)

superarts.org Over a year ago

@allenlinli I think the discussion is around iOS, not sure about macOS.

Yestay Muratov Over a year ago

What if I am using this code in pod file , and it doesnt see AppDelegate file. What should I do?

superarts.org Over a year ago

@YestayMuratov I'm not sure if I'm following, but I'll try. In general, you can still get UIApplication.shared.delegate from a shared component, but you'll not be able to know the class AppDelegate. One thing you can do is create a MyPodAppDelegateProtocol and use the interface in your pod, and in the main app, of course AppDelegate has to confirm to this protocol. But it would be good for you to ask this question separately, as the approach above doesn't sound like a good design, as it violates multiple software engineer principles, especially those about dependency.

juhan_h · Accepted Answer · 2019-08-05 01:34:49Z

Swift 4 simply has UIApplication.shared.keyWindow property, no casting necessary.

Note that iOS 13/iPadOS introduces UIScenes and explicit support for multiple windows, and thus deprecates the concept of keyWindow as it is no longer valid.

This question has an overview how to get access to scene based windows.

keyWindow is deprecated in iOS 13 developer.apple.com/documentation/uikit/uiapplication/…

nomnom · Accepted Answer · 2020-08-30 17:58:25Z

Swift 5.1

Works for me

If you are also looking for a way to deal with foreground and background modes you should try this

UIApplication.shared.windows.first(where: { $0.isKeyWindow })

rmooney · Accepted Answer · 2017-07-21 13:39:30Z

Updating superarts.org's answer for Swift 3:

if let app = UIApplication.shared.delegate as? AppDelegate, let window = app.window { MBProgressHUD.show(text, view: window) }

Iliyan Kafedzhiev · Accepted Answer · 2019-08-29 08:30:20Z

The easiest way to do that is:

in Objective-C

[UIApplication sharedApplication].windows.firstObject

in Swift

UIApplication.shared.windows.first!

Note that this works only if you do not support multiple windows.

There already are multiple windows in Cocoa. The status window, the text entry window and the main window.

rdelmar · Accepted Answer · 2014-06-14 03:33:47Z

The key window must not yet be set at the time of viewDidLoad. Your code works fine in viewDidAppear. Alternately, you can get the windows array in viewDidLoad, and get one (if there's more than one) of the windows from that array.

Irshad Ahmad · Accepted Answer · 2017-07-21 14:31:01Z

Don't call window in didLoad function call the keyWindow in viewDidAppear function of ViewController

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