Dropdown has so items until after postback

[J]

I have a DropDownList (have also tried ComboBox with the same results) that gets populated during page_load if it's not a post back.  The code executes fine and the DropDownListItems are created and appear to be added from the code behind but when the page renders the DropDownList is empty/disabled.  As soon as I do a post back (checkbox click), when it reloads, all of my DropDownLists now actually show the data and can be clicked on.

I've isolated this down to being caused when I load data into the DropDownList during page_load.  On the post back, the data loading doesn't occur (as expected) and allows the items loaded from the initial page_load to be displayed.

Any ideas why this happens or what I can do to fix it?  I've searched and searched but haven't found a solution that works.  The ComboBox exhibits the exact same behavior.

Relevant code:

DropDownList markup:

<telerik:RadDropDownList ID="cmbPayment_CardType" runat="server"
    OnSelectedIndexChanged="cmbPayment_CardType_SelectedIndexChanged"
    Width="160px" DropDownHeight="90px" DropDownWidth="160px" />

page_load from code behind:

protected void Page_Load(object sender, EventArgs e)
{
    try
    {
        if (!IsPostBack)
        {
            List<CreditCardListItem> lstCreditCards = null;

            //Load the list of accepted credit cards
            cmbPayment_CardType.Items.Clear();
            lstCreditCards = GetCreditCardsList();

            if ((lstCreditCards != null) && (lstCreditCards.Count > 0))
            {
                foreach (CreditCardListItem ccDetails in lstCreditCards)
                    cmbPayment_CardType.Items.Add(new DropDownListItem() { Text = ccDetails.DisplayName, Value = ccDetails.DisplayOrder.ToString() });
            }

            lstCreditCards.Clear();
        }
    }
    catch (Exception ex)
    {
        System.Diagnostics.Debug.Print("Error: " + ex.ToString());
    }
}

[Nencho]

Hello Juan,

Could provide us with the implementation of the GetCreditCardsList() method, which is responsible for the population with data of the RadDropDownList? In addition, I have prepared a sample project for you, based on the provided snippet of code, demonstrating the behavior at my end. Could you give it a try and let me know if I had missed something.

Note : dll files are removed from the attachment.

Regards,
Nencho
the Telerik team

[J]

Here is the code from GetCreditCardList (it's from a separate DLL that was written in VB.NET):

''' <summary>
''' Used to provide details about accepted credit cards.
''' </summary>
''' <remarks></remarks>
<Serializable()> Public Class CreditCardListItem
    Public Property DisplayName As String = String.Empty
    Public Property DisplayOrder As Byte = 0
End Class

''' <summary>
''' Gets the list of accepted credit cards.
''' </summary>
''' <returns>A List of CreditCardListItem objects detailing the credit cards that are accepted.</returns>
''' <remarks></remarks>
Public Shared Function GetCreditCardsList() As List(Of CreditCardListItem)
    Dim ret_lstCards As List(Of CreditCardListItem) = Nothing

    Dim cmdQuery As SqlCommand = Nothing
    Dim drData As SqlDataReader = Nothing
    Dim dbConn As SqlConnection = Nothing

    Try
        dbConn = New SqlConnection(ConfigurationManager.ConnectionStrings("MasterDB").ConnectionString)
        cmdQuery = New SqlCommand("Select * From CreditCardTYpes Order By TypeID, CardType", dbConn)

        dbConn.Open()
        drData = cmdQuery.ExecuteReader()

        If (drData.HasRows) Then
            ret_lstCards = New List(Of CreditCardListItem)

            While (drData.Read())
                ret_lstCards.Add(New CreditCardListItem() With {.DisplayName = drData("CardType").ToString(), .DisplayOrder = drData("TypeID").ToString()})
            End While
        End If

    Catch ex As Exception
        Debug.Print("ERROR: " & ex.ToString())

    Finally
        'Clean up
        If (drData IsNot Nothing) Then
            drData.Close()
            drData = Nothing
        End If

        If (cmdQuery IsNot Nothing) Then
            cmdQuery.Cancel()
            cmdQuery.Dispose()
            cmdQuery = Nothing
        End If

        If (dbConn IsNot Nothing) Then
            If (dbConn.State <> ConnectionState.Closed) Then
                dbConn.Close()
            End If

            dbConn.Dispose()
            dbConn = Nothing
        End If

    End Try

    Return ret_lstCards
End Function

I'll try to work up an example project for this soon.  I know I owe you guys a couple example projects right now, but I've been super booked lately.  Trying to get to it as soon as I have a chance.  Some of the issues I've had to move on from and just replace with ASP.NET controls instead while we figure them out.

[Nencho]

Hello Juan,

The functionality implemented in the method looks correct. Please make sure that ret_lstCards List is correctly populated with data and there are any exceptions, which might be caught by the Try Catch block. Did you have the chance to test the provided sample?


Kind regards,
Nencho
the Telerik team

[J]

It is correctly populated and no exceptions are raised.  I 'fixed' the issue by just replacing it with a normal ASP.NET Dropdown List with no other changes.

I should have time today to get you guys the sample project to demonstrate what is happening.

And no, I hadn't had a chance to get back to this yet and try your sample.

[J]

Not sure how, but this issue is fixed.  I went to replace my normal ASP.NET drop down lists with the Telerik ones and this time around they worked properly.  Not sure why, but it works so ... thanks.

[John]

I have the exact same issue with Telerik context menus and Combo boxes. A postback is required before they display - even if the menu items or combobox items are explicitly defined in markup. Have not found a solution. I use Ironspeed Designer to create my apps and then customise them with Telerik controls.

[Nencho]

Hello John,

Would you elaborate a bit more on the issue you are facing and which version of our controls you are currently using? In addition, please provide us with the implementation of the RadDropDownList that you use. Lastly, it would be best, if you could submit a support ticket, along with a runnable sample attached, which demonstrates the problem.

Regards,
Nencho
Telerik

[John]

Thanks Nencho. I tried to make a small bare-bones Ironspeed application that demonstrated the problem. In doing so, I worked out how to get around it. I had a radWindow and radContextMenu in the page and a radComboBox repeated in an HTML table on the same page.

By making the table a server-side table control and removing the radWindow altogether, the combobox and menu work perfectly without needing the first postback to populate.

There is a lot of code-behind and markup generated automatically by Ironspeed Designer. Sorry I don't have time to delve too deeply to work out what the interaction was that caused the problem.