unable to add control parameter from dropdownlist

on the updating of the formview.
I'm trying to add the parameter of the dropdownlist.selectedvalue which has the values of pageid and I want to update into the column of parentpageID.
e.g. insert the pageID which is the value of the selected value of the dropdownlist into the column field of parentpageID

I need to add the control parameter for the dropdownlist because I guess the sqldatasource can't find the declaratively set control  because it's in a formview.  If I put the paramter in the update parameters declaratively I get error; Could not find control 'dropdownlist1' in ControlParameter 'ParentPageID'..
Where do I need to add the parameter? in the formview updating or the sql updating?

here is my code:
Protected Sub FormView1_ItemUpdating(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.FormViewUpdateEventArgs) Handles FormView1.ItemUpdating
   &nbs ...