Please check the following link:
http://forums.asp.net/p/1117644/1736466.aspx
Example:
Dim ddl
As DropDownList =
DirectCast(sender, DropDownList)
' add an empty item on top of the list
AddEmptyItem(ddl)
Dim gvRow
As GridViewRow =
DirectCast(ddl.NamingContainer, GridViewRow)
If Not gvRow.DataItem
Is Nothing Then
Dim strModel
As String =
DirectCast(gvRow.DataItem, System.Data.DataRowView)(
"Model").ToString
ddl.ClearSelection()
Dim li
As ListItem = ddl.Items.FindByValue(strModel)
If Not li
Is Nothing Then li.Selected =
True
End If