Hello,

Thank you for posting in our forum.

Select all functionality is currently not an available feature but you can manually implement this   by following these steps:

1.       Create a header template with a check box inside.

  <HeaderTemplate>

                <input type="checkbox" id="chkBox" onchange="return CheckChanged(event);" />

                Select All

            </HeaderTemplate>

2.In the onChange client side event  manually select and deselect all item and set the corresponding values in the input box.

function CheckChanged(e) {

            var value="";

            var wdd = $find("WebDropDown1");

            for (var i = 0; i < wdd.get_items().getLength(); i++) {

                if (e.target.checked) {

                 value+= wdd.get_items().getItem(i).get_text()+", ";

                    wdd.get_items().getItem(i).select(false);

                }

                else {

                    wdd.get_items().getItem(i).unselect(false);

                }

            }

            wdd.set_currentValue(value,true);

            wdd.closeDropDown();

        }

Please refer to the attached sample and let me know if you have any questions or concerns regarding this.

Best Regards,

Maya Kirova

Developer Support Engineer

Infragistics, Inc.

http://es.infragistics.com/support