OnFilterMenuShowing

This event is fired before the filtering menu is rendered.

Fired by	RadGrid
Arguments	menu - filtering menu instance tableView - filtering menu instance gridColumn - current GridColumn object domEvent - the original browser event
Can be canceled	Yes, set eventArgs.set_cancel(true) to cancel

Example:

<telerik:RadGrid AllowFilteringByColumn="true" RenderMode="Lightweight" ID="RadGrid1" runat="server">
    <ClientSettings>
        <ClientEvents OnFilterMenuShowing ="FilterMenuShowing" />
    </ClientSettings>
    <MasterTableView AutoGenerateColumns="False" DataKeyNames="OrderID">
        <Columns>
            <telerik:GridBoundColumn DataField="OrderID" DataType="System.Int32"
                FilterControlAltText="Filter OrderID column" HeaderText="OrderID"
                ReadOnly="True" SortExpression="OrderID" UniqueName="OrderID">
            </telerik:GridBoundColumn>
        </Columns>
    </MasterTableView>
</telerik:RadGrid>

function FilterMenuShowing(sender, eventArgs) {
    if (eventArgs.get_column().get_uniqueName() == "OrderID") {
        //change the CSS class of the menu wrapper element
        eventArgs.get_menu().get_element().className = "MyClass";
    }
    else {
        eventArgs.get_menu().get_element().className = "";
    }
}