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The OnClientItemsRequesting client-side event occurs when the RadDropDownList is about to send a server-side request to load its items from the web service. This event fires before the items are added to the RadDropDownList Items collection.

The event handler receives two parameters:

  1. The instance of the RadDropDownList firing the event.

  2. An eventArgs parameter containing the following methods:

    • get_context returns a context object (implements IDictionary) that is passed to the server-side code that handles the request for items.

    • set_cancel lets you prevent the items request.

This event can be used to pass context information to the server for it to use in servicing the request, or to cancel the request. The following example uses the OnClientItemsRequesting event to sample string value to the server:

<script type="text/javascript">
    //Put your JavaScript code here.
    function clientItemRequesting(sender, eventArgs) {
        var context = eventArgs.get_context();
        context["FilterString"] = "value sent to server";
<telerik:raddropdownlist id="RadDropDownList1" runat="server" emptyselectionmessage="Select" onclientitemsrequesting="clientItemRequesting">
         <WebServiceSettings Path="WebService.asmx" Method="GetCustomerNames" />
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