Class UI
  Sub CallingSub()
    dim strOne as String = Nothing
    dim strTwo as String = Nothing
   
    if txtOne.Text <> "" then
      strOne = txtOne.Text
    end if

    if txtTwo.Text <> "" then
      strTwo = txtTwo.Text
    end if

    dim objBusiness as Business
    objBusiness.CallMe(strOne, strTwo)
  End Sub
End Class

Class Business
  Sub CallMe(ByVal strOne as String, ByVal strTwo as String)
     ....
  End Sub
End Class