I'm using native.nwTextField for some alphanumeric user input.

It's a somewhat fixed format, 2 letters and the rest numbers.

I'd like to improve on the user experience.

Using the normal keyboard flipped to numbers works but using the numeric keyboard would be soooo much nicer.

I'd like to use a button (image) to flip to numeric keyboard.
I.e. after 2 letters have been entered the user touches the button image.

I have the button working to set the keyboard to nil, but can't make it change/appear as numeric.

tried:
native:setKeyboardFocus( "number" )
partnumField.inputType = "number"

partnumField being the native.newTextField

TIA