iPad: Detecting External Keyboard

Question

My app uses a UIAccessoryView to provide additional keyboard functionality (such as forward/backward tabs and arrows keys) for the virtual keyboard, but that causes UIKeyboardDidShowNotification to fire even when a physical keyboard is present (the accessory appears at the bottom of the screen).

I'd like to check if a physical keyboard is attached when handling UIKeyboardWillShowNotification, to prevent the accessory view from appearing and to prevent my custom view from scrolling up (to make room for the non-existent virtual keyboard).

I've tried examining the UIKeyboardFrameEndUserInfoKey key, but it returns a real size for the virtual keyboard, in spite of nothing being displayed.

Is there any way to detect the presence of a physical keyboard to prevent this unwanted behaviour?

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Hmm, the plot thickens.

I tried disabling the input accessory by returning nil from the inputAccessoryView property of the Responder object which triggers the keyboard. That suppresses UIKeyboardWillShowNotification and UIKeyboardDidShowNotification when there is a physical keyboard present, but keeps these notifications when there is no such keyboard. All good so far.

Then I tried re-enabling inputAccessoryView only after UIKeyboardWillShowNotification had been received. This only fires when a virtual keyboard is needed, so it should allow me to reintroduce the accessory view in those circumstances. Or so I thought.

Unfortunately, it seems the OS doesn't check inputAccessoryView after UIKeyboardWillShowNotification, so it fails to show the accessory view when it is needed :o(

That leaves me with two options:

• Include the input accessory view, giving extra functionality for virtual keyboard users, but lose the ability to detect a physical keyboard and hence not supporting physical devices; or
• Exclude the input accessory altogether, preventing most users from accessing the extra keys, but allowing the app to work with a physical keyboard.

Not a great choice, so I'm still keen to see if anyone else has addressed this problem!

Answer 1

(This answer was suggested by Sean Heber on the Apple forums)

When you get a UIKeyboardDidShowNotification, instead of using the frame given by UIKeyboardFrameEndUserInfoKey, simply test where the view's accessory view is and use that, instead. All I do is check to see what the frame of the accessory view is and convert it to my own view's coordinate space. Then I can easily use that frame to decide what to do.

Note: When the on-screen keyboard is shown/hidden using the bluetooth keyboard's eject button, it seems that UIKit sends UIKeyboardDidShowNotification again but not a UIKeyboardWillHideNotification. This is also a confusing inconsistency, but the above workaround is still valid as the system will change the frame of the inputAccessoryView when it slides in the on-screen keyboard, so you can still adjust things accordingly.