>I want to keep the foucs on one textbox no matter the user key in any key.
>but I want the user to leave the focus if use a mouse the click on those button on the form .
>I have try to set the lostfocus event to nodefault .
>but it only can force to key foucs on that testbox.
>how can I capture the mouse click in order to left the textbox ?

Try

* LostFocus()
IF NOT MDOWN()
  NODEFAULT
ENDIF
* Or 
* Valid()
IF NOT MDOWN()
  RETURN 0
ENDIF