First there is no solution to show a alpha-numeric keyboard, there is no such keyboard.
for keyboard information:
But you can limited user's input for alpha-numeric only ("*-"will still clickable on the keyboard, but the input box doesn't accept it.)
For a simple input box (just one line, e.g. username), you must have this in your xml:
android:inputType="text"otherwise it will not show "done" key in your keyboard.