Can't Click Load-On-Demand items in RadComboBox

[Xiacon]

We have one site where we are seeing an odd behavior in RadComboBox, that I've never seen in any of our other sites. 

We have a lot of radcomboboxes throughout this site, some of which have pre-defined items, or items added on page load in the code behind. These comboboxes all work perfectly fine, exactly as expected. 

A lot of the comboboxes however use load-on-demand to query items at runtime for the user's input. ALL of these comboboxes have the same problem. They seem to perform their AJAX postback fine, and get the correct data, and the items all get added to the combobox, showing the correct data. 

The problem though is that the load-on-demand items cannot be selected. You can't click on them, you can't even use the arrow-keys to up/down to them and select one. 

The Web Developer tools in the browser don't show any javascript failing to load on page load,
they don't show any errors in the Console tab on the initial page load, or the load-on-demand postback
they don't show any errors in the Network tab on the initial page load, or the load-on-demand postback

 

This project was originally written in ASP.NET 2.0, and we are upgrading it to 4.7.2.
Updated the latest Telerik DLLs, updated the latest jQuery libraries, updated the compilation nodes in the web.config.

[Frank]

Did this issue ever get resolved? I have run into the exact same issue and am desperate for a solution.

Thank you,

Frank.

[Attila Antal]

Hi Frank,

The issue "Not being able to click an item" of a ComboBox with Load On Demand enabled could be caused by multiple things. It is important to Note that Telerik Components implement the IScriptControl interface, and they heavily depend on JavaScript. If there's a JavaScript exception on the page,. that might prevent the Combo to work as expected.

I suggest inspecting the Console tab of the Browser's DevTools for potential JavaScript errors. If you see any, you would need to eliminate them.

Here are some resources that might help in the investigation:

• Debugging Your Application on Client-Side
• Debug JavaScript

Sometimes, a server exception may appear as a JavaScript exception, and that happens if AJAX is enabled. This is what Vessy has tried to address in her answer. Please review her answers and give those suggestions a try.

 

If none of those suggestions help the case, we would need to debug the problem, but for that, we would more information that will help us replicate the issue. Namely, the markup and backend code used to create and implement the ComboBox. 

If the problem can be replicated using only the ComboBox specific code, we will review the source code and give you a solution if possible.

[Vessy]

Hello Xiacon,

Sometimes AJAX may hide both server and client-side errors. Can you, please, disable temporary the AJAX updates on the page and see if there will be any error thrown after that? Does the issue persist when the AJAX is disabled?

You can see how to achieve that easily here: 

https://www.telerik.com/support/kb/aspnet-ajax/ajaxmanager/details/how-to-disable-ajax-temporarily

Regards,
Vessy
Progress Telerik

[Xiacon]

Turning off AJAX (disabled it on the RadAjaxManager) did not help with the issue at all. It still behaves the same. No errors shown anywhere when a load-on-demand request is made, and all the right data is showing in the dropdown, but you cannot actually click/select any of the items.

I don't know if it helps any, but here is the HTTP response data coming back from the load-on-demand call:

s[]_$$_<li class="rcbItem">&#160;</li><li class="rcbItem">OK - Item in good condition</li><li class="rcbItem">Excessed</li><li class="rcbItem">AP</li>_$$_3 items_$$_False_$$_

Comboboxes which are NOT load on demand, but have their items preloaded, still behave properly.

[Vessy]

Hi Xiacon,

There is a possibility that the encrypted query string becomes too long and the server or firewall cut it, which makes it incorrect. Please check if increasing the allowed query string would fix the issue:

https://docs.telerik.com/devtools/aspnet-ajax/controls/scriptmanager/encrypt-telerik-webresource-querystring 

Example 2: Increasing the maximum query string length and URL length for an application:

. . . .
<httpRuntime maxRequestLength="204800" executionTimeout="36000" maxQueryStringLength="4096"/>
. . . .
<security>
    <requestFiltering>
        <requestLimits maxAllowedContentLength="209715200" maxQueryString="4096" maxUrl="4096" />
    </requestFiltering>
</security>

Please, ensure as well that the query string-related values (maxQueryStringLength, maxQueryString, maxUrl) in the web.config are updated accordingly to a larger value.

You can also try enabling the CDN for the Telerik resources and see if that would have any effect?

 - https://docs.telerik.com/devtools/aspnet-ajax/controls/scriptmanager/cdn-support/overview  
 - https://docs.telerik.com/devtools/aspnet-ajax/controls/stylesheetmanager/cdn-support/overview 

If none of the above helps, please, open a primary support ticket and send us a live url where we can reproduce the issue and/or a Fiddler Jam capture, so we can examine the issue further?

[Xiacon]

Increasing the various request lengths did not help.

And setting the CDN settings on broke everything. After doing that, menus (RadMenu) no longer drop down, and NO comboboxes even open up at all when clicking the drop-down arrow.

I will go ahead and set up a user with access to the system, and create a support ticket.