How to get keyboard input in 3DUI

I want to make a editable text box ,so i create a user widget and put a text box inside. When using the add to viewport function ,and put the 2D widget in my screen diretly ,it works well. But when i wrap the widget into a Actor and make it a 3DUI ,the text Box can not receive the keyboard input . How can i resolve this problem? PS: I have already put a widger interaction in the Pawn .