How to reliably detect if an external keyboard is connected on iOS 9?

Question

Previous to iOS 9, the most reliable method of determining whether an external keyboard is connected was to listen for UIKeyboardWillShowNotification and make a

Answer 1

If you make the toolbar irrelevant then the keyboard doesn't show up. Do this by blanking out its left and right groups (at least on iOS 12.4):

textField.inputAssistantItem.leadingBarButtonGroups = []
textField.inputAssistantItem.trailingBarButtonGroups = []

...and in case it helps here is a swifty way to observe:

// Watch for a soft keyboard to show up
let observer = NotificationCenter.default.addObserver(forName: UIWindow.keyboardWillShowNotification, object: nil, queue: nil) { notification in
    print("no external keyboard")
}

// Stop observing shortly after, since the keyboard should have shown by now
DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
    NotificationCenter.default.removeObserver(observer)
}