KeyWindow

This package provides a way to share values from the key window to all other parts of your application. (the key window in macOS/iPadOS is the window that currently responds to keyboard shortcuts).

The main use-case of this package is to make it possible to pass values from the key window to views in the commands section of a SwiftUI lifecycle application.

import KeyWindow

@main
struct ExampleWindowReaderApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView().observeWindow()
        }.commands {
            CommandMenu("MyMenue") {
                MenuButton()
            }
        }
    }
}

Notice it is important to wrap the ContentView of your app with the .observeWindow() modifier, this enables KeyWindow to observe this window and the values it publishes.

Within our ContentView and its children we can publish values in a similar way to publishing Preferences.

First create a struct that conforms to KeyWindowValueKey and declare the value type.

struct SelectedProjectWindowValueKey: KeyWindowValueKey {
    typealias Value = Binding<UUID>
}

struct SelectedProjectTitleWindowValueKey: KeyWindowValueKey {
    typealias Value = String
}

Then to provide these within our views we can set these using .keyWindow(SelectedProjectWindowValueKey.self, $projectSelection). This will bubble up and when the window becomes key then we can read these values within our MenuButton.

struct MenuButton: View {
    @KeyWindowValue(SelectedProjectTitleWindowValueKey.self)
    var title: String
    
    @KeyWindowValueBinding(SelectedProjectWindowValueKey.self)
    var selectedProject: UUID?

    var body: some View {
        Button(action: {
            // Delete the selectedProject
            self.selectedProject = // some other project
        }, label: {
            Text("Delete \(title)")
        })
    }
}

NOTE you can't use @KeyWindowValue or @KeyWindowValueBinding in a struct MyCommands: Commands type. You need to extract the Buttons from the Commands body into their own Views so that you can use these property wrappers (this is a limitations of SwiftUI).

For a little more detail on common pattern is to share the document from the key window so that is it accessible within the commands section this blog post covers this use-case.

You can also use @KeyWindowValue and @KeyWindowValueBinding in your other views but be careful to ensure they do not result in .keyWindow modifiers being re-called otherwise it is possible to get into a loop. The best way to do this is to set all your .keyWindow high up in your view hierarchy and only use @KeyWindowValue and @KeyWindowValueBinding on deeply nested child views.

In addition this package also provides a EnvironmentValues.isKeyWindow that can be read to detect if the view is in the key window. (you might use this to change the style of rendering). Note this is not the same as scenePhase, scenePhase indicates if the scene is active not if the window for the view is in the Key Window. On iPadOS and macOS you can have multiple scenes active and on macOS each Scene can have many windows but only one of them will be key at any given time.

Finding the correct property wrapper for your value type

Depending on the data type you are trying to share from your key window there are a few different property wrappers you can use to read the value:

Type	Property Wrapper	Comment
"String" , 42 or MyStruct	@KeyWindowValue	For performance reasons it is best if these value types conform to equatable
Binding<MyStruct>	@KeyWindowValueBinding	-
Binding<Optional<MyStruct>>	@KeyWindowOptionalValueBinding	-
Observable Object	@KeyWindowObservableObject	The Key in this case needs to conform to KeyWindowObservableObjectKey and provide a defaultValue