Note that not all windows are necessarily NSWindows, and that NSWindow only provides an interface to windows in your own address space. The supported way to access every window is the CGWindow API. Take a look at the Son of Grab sample code to see how it’s done.
Update for OS X El Capitan The hack I described in my original answer below is not needed on OS X El Capitan anymore. The NSVisualEffectView’s maskImage should work correctly there, if the NSWindow’s contentView is set to be the NSVisualEffectView (it’s not enough if it is a subview of the contentView). Here’s a sample … Read more
That’s a Cocoa design decision: windows without title or resize bar cannot become key window by default. If you want a titleless window to be able to become a key window, you need to create a subclass of NSWindow and override -canBecomeKeyWindow as follows: – (BOOL)canBecomeKeyWindow { return YES; }
I just used the following variant in AppDelegate, the content of ContentView and others can be any func applicationDidFinishLaunching(_ aNotification: Notification) { // Create the SwiftUI view that provides the window contents. let contentView = ContentView() .edgesIgnoringSafeArea(.top) // to extend entire content under titlebar // Create the window and set the content view. window = … Read more
To change the window level you can’t do it inside viewDidload because view’s window property will always be nil there but it can be done overriding viewDidAppear method or any other method that runs after view is installed in a window (do not use it inside viewDidLoad): Swift 4 or later override func viewDidAppear() { … Read more