Responding to keyboard modifiers on macOS in SwiftUI

New in macOS 15, we can now use onModifierKeysChanged(mask:initial:_:) to update our views when keyboard modifiers are held down.

It's common to reveal additional details and advanced settings when the user holds down the option key in a Mac app. Here is how we can use the new API to show a button only while the option modifier is pressed.

struct ContentView: View {
    @State var optionPressed = false
    
    var body: some View {
        VStack(alignment: .trailing) {
            Toggle("Show emoji", isOn: .constant(false))
            Spacer()
            if optionPressed {
                Button("Advanced") {
                    /// TODO: open advance settings sheet
                }
            }
        }
        .onModifierKeysChanged(mask: .option) { old, new in
            optionPressed = new.contains(.option)
        }
    }
}

The new onModifierKeysChanged() method is only available on the latest macOS, so if you need to respond to modifier keys on iPadOS or older macOS versions, check out my other post Reading keyboard modifiers on iPad in SwiftUI.

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