The selectedIndexChanging event occurs before users changes the checked state of an item in RadCheckBoxList. This event can be canceled.

The event handler receives two parameters:

  1. The instance of the loaded RadCheckBoxList control.

  2. An eventArgs parameter of type Telerik.Web.UI.ButtonListCancelEventArgs, containing the following properties and methods:

    • get_item() - returns an instance of type Telerik.Web.UI.ButtonListItem (the clicked item).
    • get_cancel() - sets a bool value that indicates whether the event will be canceled. Setting true means the event will be canceled.
    • set_cancel() - returns a bool value that indicates whether the event was canceled. True means the event is canceled.

Example 1: Handling RadCheckBoxList OnItemCheckedChanging event.

<script type="text/javascript">
    function OnItemCheckedChanging(sender, args) {
        var selectedLanguage = args.get_item().get_text();
        var toChange = !confirm("You checked on " + selectedLanguage + " language!");

<telerik:RadCheckBoxList runat="server" ID="RadCheckBoxList1">
    <ClientEvents OnItemCheckedChanging="OnItemCheckedChanging" />
        <telerik:ButtonListItem Text="English" Selected="true" />
        <telerik:ButtonListItem Text="German" />
        <telerik:ButtonListItem Text="French" />

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