combo box click to expand

I'm trying to click anywhere on the combo box to expand/show the popup.
As it stands now, by default you have to click the 'v' to expand the combo box. I've done extensive searching for many hours, but havent found any solutions to work. Here is the only solution I found, but simply doesn't work

obj.onControlClicked = function() {
this.showPopup();
}

I'm not sure why either, when it clearly should work. I'm using version 2.6
Any help would be much appreciated, thanks