dropdownlist does not show any values after postback

[Karineh_1]

Hi everyone,
I am populating a dropdownlist based on the selection from another dorpdownlist. As long as there is no postback happening, I see the list getting populated correctly but after a postback, my dropdownlist is empty.
I am setting the DataValueField property of the ddl that I populate at runtime and the ViewStateMode for that ddl is set to Enabled.
Does anyone know what could be the reason?

[JorgeM]

It would help to see your code. Its challenging to guess what is happening based on a description.

after a postback, my dropdownlist is empty.

Are you doing something to clear the dropdown at page_load? If you are building the drop down at page load, you may want to detect !IsPostBack so you only modify the drop down at first load and allow the viewstate to do its thing.

again, show your code so we can take a look.

[geniusvishal]

May be you should check whether your dropdownlist is getting binded again on each postback..
If not then put the binding code inside the !page.ispostback section so that it will be binded on each postback.

[Karineh_1]

Thank you for your responses. I need to add one more piece of information. Both of these ddls are inside a Formview. I noticed that if I move the ddl that I populate programmatically (the one that loses its contents afte postback) outside of the Formview, then it retains its contents. The same thing happens with a textbox that resides inside the Formview. It is supposed to take user comments. In Insert mode, it loses its contents after postback but in Edit mode it retains. What is specific about Formviews?
Here is the code and thanks again for your comments.

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    If Not IsPostBack Then

        If NavHelper.User.UserName = "" Then
            Dim UserIP As String
            Dim UserLogin As String
            Dim UserEmail As String
            UserIP = HttpContext.Current.Request.UserHostAddress
            UserLogin = HttpContext.Current.Session("Username")
            UserEmail = HttpContext.Current.Session("Email")
            GetUserInfo()

            CurrentRFQ = Nothing
            If NavHelper.RFQ.ID = -1 Then
                formview_RFQ.ChangeMode(FormViewMode.Insert)
                tabpanelCustomerParts.Visible = False
                tabpanelDocuments.Visible = False
                tabpanelReviews.Visible = False
                tabpanelRFQReviewHistory.Visible = False
                listview_CustomerParts.Dispose()

            Else
                formview_RFQ.ChangeMode(FormViewMode.Edit)
                listview_ReviewContracts_Initial.EditIndex = 0
                SessionHelper.CurrentObject = TAA.Library.RFQ.GetObject(NavHelper.RFQ.ID)
                mRFQ = DirectCast(SessionHelper.CurrentObject, TAA.Library.RFQ)
                Dim UserdeptTotal As Long
                UserdeptTotal = HttpContext.Current.Session("DepartmentTotal")
                datasource_BuyerNVList.Dispose()
                datasource_BuyerNVList.DataBind()
                If formview_RFQ.FindControl("ddlCompanyBuyerNVList") IsNot Nothing Then
                    Dim ddl As DropDownList = DirectCast(formview_RFQ.FindControl("ddlCompanyBuyerNVList"), DropDownList)
                    FillCompanyNameDropDownList(ddl)
                End If
                tabpanelCustomerParts.Visible = True
                tabpanelDocuments.Visible = True
                tabpanelReviews.Visible = True
                tabpanelRFQReviewHistory.Visible = True
                If NavHelper.RFQ.Copy = True Then
                    SetModifyCopy()
                End If
                End If
        Else    'IsPostBack
                datasource_BuyerNVList.Dispose()
                datasource_BuyerNVList.DataBind()                    
                Dim ddl As DropDownList
                If (formview_RFQ.CurrentMode = FormViewMode.Insert) Then
                    ddl = DirectCast(formview_RFQ.FindControl("ddlCompanyBuyerNVListInsert"), DropDownList)
                ElseIf formview_RFQ.FindControl("ddlCompanyBuyerNVList") IsNot Nothing Then
                    ddl = DirectCast(formview_RFQ.FindControl("ddlCompanyBuyerNVList"), DropDownList)
                End If
                FillCompanyNameDropDownList(ddl)
        End If
    End If
End Sub