Update gridview with a button outside of the gridview

I have a gridview control where one of the columns contains a drop-down list box control.  Outside of the gridview I have an Update button.  I would like the OnClick event of the Update button to trigger an update but only for the rows where the drop-down value was changed.

Attached is my OnClick function so far.  I know how to step through the rows in the gridview, I'm just not sure how to do my comparison.

Thanks.

   

Protected Sub btnUpdate_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnUpdate.Click
      Try
 
         For Each gv As GridViewRow In grdSearch.Rows
 
            Dim ddlSelectedValue As DropDownList = CType(gv.FindControl("ddlAssignedTo"), DropDownList)
 
            If ddlSelectedValue.SelectedValue <> Compare to What??? Then
               'code to perform update here
            End If
         Next
 
      Catch ex As Exception
 
      End Try
 
   End Sub

Select allOpen in new window