In Development
Last Updated: 05 Sep 2023 10:34 by ADMIN
Scheduled for R3 2023
The RadMultiSelect implementation has one error that WCAG 4.1.1 parsing is catching. There is a duplicate span with the same id.

Found in the page source of the demo page (similar to how I implemented as well):

<select name="ctl00$ContentPlaceholder1$RadMultiSelect1" multiple="" id="ctl00_ContentPlaceholder1_RadMultiSelect1" class="RadMultiSelect RadMultiSelect_Silk" style="width:400px;">
<span id="ctl00_ContentPlaceholder1_RadMultiSelect1_WebServiceCDS" style="display:none;"></span><input id="ctl00_ContentPlaceholder1_RadMultiSelect1_ClientState" name="ctl00_ContentPlaceholder1_RadMultiSelect1_ClientState" type="hidden" />
</select><span id='ctl00_ContentPlaceholder1_RadMultiSelect1_WebServiceCDS' style='display:none'></span>
Last Updated: 08 Jun 2023 14:16 by ADMIN
Release R2 2023 SP1

I am getting the following error when using RadMultiSelect with over 13000 records:

Error InnerException Message: Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property.
 Error InnerException StackTrace:    at System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object obj, StringBuilder output, SerializationFormat serializationFormat)
   at Telerik.Web.UI.AdvancedJavaScriptSerializer.Serialize(Object obj)
   at Telerik.Web.UI.RadMultiSelect.DescribeItems(IScriptDescriptor descriptor)
   at Telerik.Web.UI.RadMultiSelect.DescribeComponent(IScriptDescriptor descriptor)
   at Telerik.Web.UI.ScriptRegistrar.GetScriptDescriptors(Control control)
   at Telerik.Web.UI.RadDataBoundControl.GetScriptDescriptors()
   at System.Web.UI.ScriptControlManager.RegisterScriptDescriptors(IScriptControl scriptControl)
   at Telerik.Web.UI.RadDataBoundControl.RegisterScriptDescriptors()
   at Telerik.Web.UI.RadDataBoundControl.Render(HtmlTextWriter writer)
   at Telerik.Web.UI.RadMultiSelect.Render(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)

I already have <jsonSerialization maxJsonLength="2147483647"> in my web.config but still errors out.

Telerik.Web.UI Version: 2022.2.622.45

Seems similar to this issue:

But updating to higher version than 2020 didn't seem to solve it. Was the fix only for RadMap?

As it was for other

Last Updated: 24 Apr 2023 07:34 by Nitin

Scenario: Server paging and filtering are enabled for RadMultiSelect.

  1. Filter to an item that is not present on the default list of items and select it.
  2. Expand the drop-down by clicking on the Input element.

Currently, the Selected item is not displayed within the drop-down even if it is still selected in the control.

The expected behavior is to have all selected items in the dropdown even when they are not part of the currently filtered set of items.

Last Updated: 26 Oct 2022 14:48 by ADMIN
Scheduled for R3 2022 SP1
Created by: Peter
Comments: 1
Category: MultiSelect
Type: Bug Report

RadMultiselect control has ClearButton property which should enable displaying the button for clearing all the selected options...

However, eventhough I have this property turned on I don't see any button for clearing the values...  I can only go to the "expected" position for the button and then my mouse cursor is changed and after clicking all the values are cleared as expected... 

Last Updated: 28 Jul 2022 08:51 by Peter
Created by: Peter
Comments: 0
Category: MultiSelect
Type: Bug Report
When MapValueTo="dataItem" the serialization of the data item errors out as the object passed for serialization does not have the .ToJSON() method. 
Last Updated: 28 Jun 2022 13:15 by Peter


I wanted to implement RadComboBox combined with checkboxes and load on demand approach.

However, this page explained it is not possible and advised to use RadMultiSelect with Virtualization

I checked the page and demo is explained via web service... 

Is there a demo where it would be explained that when I type e.g. 3 characters some function would be called (e.g. OnItemsRequested) and in the server I would call database and fill the required data ? We don't have web service for providing the data... In code-behind we always access databases.



Last Updated: 08 Nov 2021 12:26 by ADMIN
Release R1 2022
Created by: Asif Pathan
Comments: 0
Category: MultiSelect
Type: Bug Report

The SelectionChanged event is fired before Page_Load, hence when the ViewState is applied, it overrides the changes made inside the OnSelectionChanged handler.

Example - Clearing the CheckBox selection of a RadComboBox inside SelectionChanged

Workaround - Create a custom boolean property on the page and set it to true inside the SelectionChanged. Then, in Page_Load or the OnLoad event of any control, execute your logic based on the custom boolean property value.

Last Updated: 04 Feb 2021 00:42 by Hugo Augusto

A "Control 'RadMultiSelect1' referenced by the ControlToValidate property of 'MultiSelectValidator1' cannot be validated" error is thrown when the RadMultiSelect id is passed to the ControlToValidate property of the RequiredFieldValidator or CustomValidator.

Workaround: Using a CustomValidator with no ControlToValidate

<telerik:RadMultiSelect ID="RadMultiSelect1" runat="server" DataTextField="text" DataValueField="value">
        <telerik:MultiSelectItem Text="Item 1" Value="1"></telerik:MultiSelectItem>
        <telerik:MultiSelectItem Text="Item 2" Value="2"></telerik:MultiSelectItem>
        <telerik:MultiSelectItem Text="Item 3" Value="3"></telerik:MultiSelectItem>

<telerik:RadButton runat="server" ID="RadButton1" Text="Postback" AutoPostBack="true" />

<asp:CustomValidator ErrorMessage="Please select an item" ClientValidationFunction="ClientValidationFunction" runat="server" />
    function ClientValidationFunction(sender, args) {
        var multiselect = $find("<%= RadMultiSelect1.ClientID %>");

        if (multiselect.get_value().length == 0) {
            args.IsValid = false;

Last Updated: 06 Nov 2020 20:06 by ADMIN
Created by: Aurigo IT
Comments: 1
Category: MultiSelect
Type: Feature Request
Currently, to make the MultiSelect control work in an EditTemplate of a Grid in Batch EditMode, custom implementation is needed.
Last Updated: 21 Oct 2020 15:39 by ADMIN
Created by: Chris Vaughn
Comments: 0
Category: MultiSelect
Type: Bug Report

Scenario 1)

- Set MultiSelect1.Enabled=false; 
- Do a postback;

Expected: MultiSelect remain disabled
Actual: MultiSelect gets enabled

Workaround: set MultiSelect1.Enable = false instead of .Enabled.

Scenario 2)

- Add a MultiSelect inside asp:Panel
- Disable the asp:Panel

Expected: MultiSelect is disabled
Actual: MultiSelect remains enabled


Last Updated: 22 Jun 2020 17:19 by ADMIN
<telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" RenderMode="Lightweight" DecoratedControls="All" />
<telerik:RadMultiSelect runat="server"
    Placeholder="Select attendees..."
        <telerik:MultiSelectItem Text="Steven White"></telerik:MultiSelectItem>
        <telerik:MultiSelectItem Text="Nancy King"></telerik:MultiSelectItem>
        <telerik:MultiSelectItem Text="Nancy Davolio"></telerik:MultiSelectItem>