Question

Yes, it’s the infamous viewstate again!

Now I am aware that problems can ocurr if you load controls in the wrong order or if the viewstate IDs are incorrect after postbacks etc etc.

But my issue is that I am not really creating any controls dynamically – I only have one user control on the page.

More importantly, the issue seems to be occuring with just one user.

What could be the problem? Corrupt browser cache?

Any help appreciated.

thanks,

KS

Hi, ok – so I’ve narrowed it down a bit more. When I select an item from a drop down list control (which is a UserControl) – and then attempt to rebind my grid using the selected value, the error occurs.

The selectedvalue on postback seems to be zero every time (because the control is not in the viewstate somehow?!).

The UserControl (containing the dropdownlist) is added at design-time.

Hi, thanks for your reponse. What logic should I try moving to OnPreRender?

Another thing I missed…

-The first bind of grid works fine (on first time page load).
-Selecting value from dropdownlist causes postback in which grid is bound again using values – works fine also.
-When I click another button (which also triggers binding for grid), the viewstate error occurs.

Below is some code:

---

UserControl Source:

Imports iMWeb_BUL
Imports System.Data

Partial Class TitleList
Inherits System.Web.UI.UserControl

Public Event IndexHasChanged(ByVal sender As Object, ByVal e As CommandEventArgs)

Public Property TitleID() As Integer
    Get
        Return IIf(DDL_Titles.SelectedValue = Nothing, 0, DDL_Titles.SelectedValue)
    End Get
    Set(ByVal value As Integer)
        Try
            DDL_Titles.SelectedValue = value
        Catch
        End Try
    End Set
End Property

Public ReadOnly Property TitleTable() As DropDownList
    Get
        Return DDL_Titles
    End Get
End Property

Public ReadOnly Property TitleName() As String
    Get
        If DDL_Titles.SelectedValue > 0 Then
            Return DDL_Titles.SelectedItem.ToString()
        Else
            Return Nothing
        End If
    End Get
End Property

Public Sub DDL_Titles_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DDL_Titles.SelectedIndexChanged
    Dim ee As CommandEventArgs = New CommandEventArgs(DDL_Titles.SelectedValue, Nothing)
    RaiseEvent IndexHasChanged(Me, ee)
End Sub

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    If Not Page.IsPostBack Then
        'bind dropdownlist
        common.BindDDLs("MovieListDemo", "[SP_ListTitlesDEMO]", "MOV_ID", "movie_name", true, DDL_Titles, Nothing)
    End If
End Sub

End Class

Main page logic (pseudo):

Sub Page_Load
 If not postback
  bindGrid()
 End If

If UserControl1.IndexChanged
 bindGrid()
End If

If Button1.clicked
 bindGrid() <---- error occurs here
End if

Sub bingGrid
 fetch data passing param TitleList1.TitleID (usercontrol)
End Sub

End Sub

Answer 1

Try moving your logic into OnPreRender

and/or In the OnLoad event, build the page with the current parameter, so that the DropDownList can get rebuilt correctly, then redraw the page with the new parameter and see if the problem goes away.

What’s likely happening is the DropDownList has viewstate but the content of the control has changed before ViewState is reprocessed.