ASP.Net Trick: Getting rid of viewstate on DropDownLists

If you’ve used ASP.Net for any amount of time, you quickly realize how much it loves to dump into the viewstate. Now, I’m not claiming I’m a saint in this area, but I have been learning as I go to recognize what operations will fill the viewstate and work to prevent them.

One trick I learned recently is to re-bind your DropDownList on every postback, inside of the DropDownList’s Init event handler. You can also pull in the postback value from the Request.Form collection and set the DropDownList’s SelectedValue to what it should be. Observe the following example:

   1: Protected Sub ddlMyDropDownList_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles ddlMyDropDownList.Init

   2:     Dim db = New MyDataContext()

   3:  

   4:     Dim q = From s In db.States _

   5:             Order By s.StateName _

   6:             Select New ListItem(s.StateName, s.StateAbbrev)

   7:  

   8:     ddlMyDropDownList.Items.AddRange(q.ToArray())

   9:  

  10:     Dim r = Request(ddlMyDropDownList.UniqueID)

  11:     If r IsNot Nothing Then ddlMyDropDownList.SelectedValue = r

  12: End Sub

Don’t forget to set “EnableViewState=False” on your DropDownList.