One, probably a stupid question. Is it possible to choose which keys to appear on Android keyboard (other than just setting input type)? For example, can I specify I only want to show keys: 0,1,2,3,4,5,6,7,8,9,A,B?
Or should I write completely custom keyboard for it?
I don't care about layout and styling.
I need it only for one activity.
Is it possible to choose which keys to appear on Android keyboard (other than just setting input type)?
Write your own input method editor and hope that the user elects to enable and use it.
Otherwise, no.
can I specify I only want to show keys: 0,1,2,3,4,5,6,7,8,9,A,B?
No. Bear in mind that there are hundreds of input method editors, not just one. Unless you are deploying only to a single device model, there will be many editors that your users will encounter.