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The OnClientDropDownOpening client-side event occurs when the drop-down is about to expand, showing its child buttons.

The event handler receives two parameters:

  1. The instance of the toolbar firing the event.

  2. An eventArgs parameter containing the following methods:

  • get_item returns a reference to the RadToolBarItem that is about to expand. In this case it is a drop-down.

  • set_cancel lets you prevent the toolbar from showing its children.

  • get_domEvent - returns the browser's event object.

You can use this event to control when drop-down can expand, or customize the child buttons before the toolbar expands:

    function OnClientDropDownOpening(sender, args) {
        var status = $get("hdCurrentStatus");
        var dropDown = args.get_item();
        if (status.value == "")
        else {

<telerik:RadToolBar RenderMode="Lightweight" ID="RadToolBar1" runat="server" Orientation="Horizontal" 
    <CollapseAnimation Duration="200" Type="OutQuint" />
        <telerik:RadToolBarButton Text="button1" runat="server">
        <telerik:RadToolBarDropDown Text="dropdown" runat="server">
                <telerik:RadToolBarButton Text="Button2" runat="server">
<asp:HiddenField ID="hdCurrentStatus" runat="server" Value="you can set this value to blank" />
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