Error combining CheckBoxes, AutoPostBack and EnableVirtualScrolling

[Rubens]

I have this ASPX code:

<telerik:RadComboBox runat="server" ID="instituicao" Width="450" CheckBoxes="true"
        AutoPostBack="true" ItemsPerRequest="10"
        EnableLoadOnDemand="True" ShowMoreResultsBox="true" EnableVirtualScrolling="true"
        OnItemChecked="instituicao_ItemChecked" OnItemsRequested="instituicao_ItemsRequested" />

And this code behind:

protected void instituicao_ItemsRequested(object sender, RadComboBoxItemsRequestedEventArgs e)
{
    DataTable dt = GetData();
    int total = dt.Rows.Count;
    int itemOffset = e.NumberOfItems;
    int endOffset = Math.Min(itemOffset + instituicao.ItemsPerRequest, total);
    e.EndOfItems = endOffset == total;
    instituicao.Items.AddRange(
        dt.Rows.OfType<DataRow>().Skip(itemOffset).Take(endOffset - itemOffset)
               .Select(i => new RadComboBoxItem(i["Id"] as string, i["Id"] as string)));
}

protected void instituicao_ItemChecked(object sender, RadComboBoxItemEventArgs e)
{
    // do stuff
}

private DataTable GetData()
{
    DataTable dt = new DataTable();
    dt.Columns.Add("Id", typeof(string));
    for (int i = 1; i <= 100; i++ )
    {
        DataRow row = dt.NewRow();
        row["Id"] = i;
        dt.Rows.Add(row);
    }
    return dt;
}

When I check an item I got this error and my code is never executed:

[ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index]
   System.Collections.ArrayList.get_Item(Int32 index) +7487944
   System.Web.UI.StateManagedCollection.System.Collections.IList.get_Item(Int32 index) +12
   Telerik.Web.UI.ControlItemCollection.get_Item(Int32 index) +48
   Telerik.Web.UI.RadComboBoxItemCollection.get_Item(Int32 index) +37
   Telerik.Web.UI.RadComboBox.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +238
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +175
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1565

Any clues?

[Kalina]

Hi,

I am afraid that simultaneous usage of CheckBoxes and Load On Demand is not supported.
Please take a look at the "CheckBox Support" help article where this topic is described in details.
Additionally at this online demo you can test the RadComboBox behaviour under different configurations.

Regards,
Kalina
the Telerik team