I have a scenario with multiple RadComboBoxes that don’t seem to fire the Itemsrequested server event  prior to receiving the response from the previous callback.  Here is a page that I wrote to show the problem. When the normal ASP.NET drop down changes indexes, it will make a callback that has a 5 seconds delay in it. If you press the drop down button for either of the RadComboBoxes during this time, it will display loading but never return. You have to click out of the combo box and then back in it to get the items to load.

RadComboBox 1 also has an onblur that calls an AJAX callback to a 5 second delay. If you try to drop down RadComboBox 2 during this delay, it will just show loading and not update.

Do you have any suggestion as to what might be causing this and how to get around it? Ideally the combo boxes will be able to either load during the callback or queue the request so that it will start when the previous callback is complete.

System;

System.Collections.Generic;

System.Data.Linq;

System.Linq;

System.Runtime.Serialization;

System.ServiceModel;

System.ServiceModel.Activation;

System.ServiceModel.Web;

System.Text;

System.Web.Services;

Telerik.Web.UI;

QUARK.webservices

{

[

ServiceContract(Namespace = "")]

[

AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]

public class strange

OperationContract]

public RadComboBoxData LoadDataTemplates(RadComboBoxContext context)

{

RadComboBoxData result = new RadComboBoxData();

quarkDataContext quarkdb = new quarkDataContext();

var allTemplates = from DEVICE_TYPE in quarkdb.DEVICE_TYPEs

orderby DEVICE_TYPE.DESC

select new RadComboBoxItemData

string text = context.Text;

if (!String.IsNullOrEmpty(text))

{

allTemplates = allTemplates.Where(item => item.Text.StartsWith(text));

}

int numberOfItems = context.NumberOfItems;

var templates2 = allTemplates.Skip(numberOfItems).Take(10);

result.Items = templates2.ToArray();

int endOffset = numberOfItems + templates2.Count();

int totalCount = allTemplates.Count();

if (endOffset == totalCount)

result.EndOfItems =

true;

result.Message =

String.Format("Items <b>1</b>-<b>{0}</b> out of <b>{1}</b>",

endOffset, totalCount);

return result;

}

}

}

telerik:RadComboBox ID="drp_hosttemplate" Runat="server"

Skin="Web20" Width="177px" EnableLoadOnDemand="True"

EnableVirtualScrolling="True" ShowMoreResultsBox="True"

EnableItemCaching="True" >

<WebServiceSettings Method="LoadDataTemplates" Path="webservices/strange.svc" />

<ExpandAnimation Type="InOutElastic" />

<CollapseAnimation Type="InOutElastic" />

</telerik:RadComboBox>

I’m using a web service to feed the search as you type combo box on my page.  If the search returns 0 results I get the following error:

Microsoft Jscript runtime error: ‘Items’ is null or not an object

It works fine if results are returned.  Below is the code for the RadComboBox and below that is the web service method I’m using.  Any assistance would be greatly appreciated.

Experienced this problem with both 2010 Q1 and now Q2 Beta.

RadComboBox Snippet:

<telerik:RadComboBox ID="rcmbClients" runat="server" EnableLoadOnDemand="true"
     ShowMoreResultsBox="true" EnableVirtualScrolling="true"
     TabIndex="1" EnableItemCaching="true" EnableViewState="false" EmptyMessage="-- enter text --"
     NoWrap="true" ShowWhileLoading="false"
     OnSelectedIndexChanged="rcmbClients_SelectedIndexChanged"
     AutoPostBack="true" Width="500" WebServiceSettings-Method="GetFilteredClients"
     Filter="Contains" ItemRequestTimeout="300" WebServiceSettings-Path="~/RadService.svc"
     AllowCustomText="true">
 </telerik:RadComboBox>  

Web Service Snippet:

[ServiceContract(Namespace = "")]
 [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
 public class RadService
 {
  [OperationContract]
  public RadComboBoxData GetFilteredClients(RadComboBoxContext context)
  {
      try
      {
              
         RadComboBoxData result = new RadComboBoxData();
         ClientBL clientBL = new ClientBL(); 
         IList<ShortClient> clients = clientBL.GetFilteredShortClients(context.Text.Replace("%", "[%]").Replace("&squote", "[']"));
         IEnumerable<RadComboBoxItemData> allDataItems = from client in clients

                                                         select new RadComboBoxItemData()

                                                         {

                                                             Text = client.DisplayName,

                                                             Value = client.ID.ToString()

                                                         };

         int numberOfItems = context.NumberOfItems;

         IEnumerable<RadComboBoxItemData> pageOfDataItems = allDataItems.Skip(numberOfItems).Take(500);

         result.Items = pageOfDataItems.ToArray();

         int endOffSet = numberOfItems + pageOfDataItems.Count();

         int totalCount = allDataItems.Count();

         if (endOffSet == totalCount)

             result.EndOfItems = false;

         result.Message = String.Format("Items <b>1</b>-<b>{0}</b> out of <b>{1}</b>", endOffSet, totalCount);

         return result;

     }

     catch (Exception ex)

     {

         string target = context.Text;

         LogManager logManager = new LogManager();

         logManager.Log(TraceEventType.Error, "Search Criteria Submitted By User: \"" + context.Text + "\""  + Environment.NewLine + ex.Message.ToString());

         throw;

     }

}