Programatically changing button text and actions when a modifier key is pressed

Question

I would like to change the text of an NSButton when the ⌥ Option key is pressed - similar to the copy dialog when colliding files are detected on OS X which changes "Keep Both" to "Merge" when the option key is held.

In my case, I would like to change a button with text, say, "delete" to "quit" when I hold the option key. Additionally, its functionality should change in accordance with its title, much like the options in the Copy dialog.

Can this be done programatically in Swift?

Answer 1

You can subscribe using addLocalMonitorForEvents(matching:) and detect if option key pressed like this:

var optionKeyEventMonitor: Any? // property to store reference to the event monitor

// Add the event monitor
optionKeyEventMonitor = NSEvent.addLocalMonitorForEvents(matching: .flagsChanged) { event in
    if event.modifierFlags.contains(.option) {
        self.button.title = "copy"
        self.button.action = #selector(self.copyButtonClicked(_:))
    } else {
        self.button.title = "delete"
        self.button.action = #selector(self.deleteButtonClicked(_:))
    }  
    return event
}

@IBAction func copyButtonClicked(_ sender: Any) {
    Swift.print("Copy button was clicked!")
}

@IBAction func deleteButtonClicked(_ sender: Any) {
    Swift.print("Delete button was clicked!")
}

Remember to remove the event monitor when you are done:

deinit {
    if let eventMonitor = optionKeyEventMonitor {
        NSEvent.removeMonitor(eventMonitor)
    }
}

If you don't want a separate method called depending on the option key state, you can check modifierFlags when button is clicked instead:

@IBAction func buttonClicked(sender: NSButton) {
    if NSEvent.modifierFlags().contains(.option) {
        print("option pressed")
    } else {
        print("option not pressed")
    }
}