Minimize the SelectedIndexChanged server events fired when SelectionMode is Multiple for RadListBox

PROBLEM

The SelectedIndexChanged server-side event is fired for each item when dragging to select multiple items in RadListBox

DESCRIPTION

This is expected as the OnClientSelectedIndexChanged event checks if the AutoPostBack is true, and if it is, it triggers a postback.

SOLUTION

The solution is to set the AutoPostBack property to false in the mousedown event and then when the selection finishes, to trigger the postback manually:

ASP.NET

<telerik:RadListBox ID="lbFilter1" runat="server"
    SelectionMode="Multiple"
    OnClientLoad="OnClientLoad"
    OnSelectedIndexChanged="lbFilter1_SelectedIndexChanged"
    AutoPostBack="true">
    <Items>
        <telerik:RadListBoxItem Text="Item 1" />
        <telerik:RadListBoxItem Text="Item 2" />
        <telerik:RadListBoxItem Text="Item 3" />
        <telerik:RadListBoxItem Text="Item 4" />
        <telerik:RadListBoxItem Text="Item 5" />
        <telerik:RadListBoxItem Text="Item 6" />
    </Items>
</telerik:RadListBox>

JavaScript

<script>
    function OnClientLoad(sender, args) {
        var listbox = sender;
        $telerik.$(listbox.get_element()).find(".rlbList").on({
            mousedown: function () {
                listbox.set_autoPostBack(false);
            },
            mouseup: function () {
                listbox.set_autoPostBack(true);
                listbox.postback({
                    type: Telerik.Web.UI.ListBoxCommand.SelectedIndexChanged
                });
            },
            mouseout: function (ev) {
                if ($telerik.$(ev.target).closest(".rlbList")[0] != this) {
                    listbox.set_autoPostBack(true);
                    listbox.postback({
                        type: Telerik.Web.UI.ListBoxCommand.SelectedIndexChanged
                    });
                }
            }
        })
    }
</script>

C#

protected void lbFilter1_SelectedIndexChanged(object sender, EventArgs e)
{
       // custom logic here...
}

VB

Protected Sub lbFilter1_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
     `custom logic here...
End Sub