Making Gear Pop-up Menus
New Apple engineer Corbin Dunn posted a tip for how to create pop-up menus that emanate from the “action” button, as seen in the Finder and Mail. However, it looks to me like his method will cause the menu to pop-up on mouse-up rather than mouse-down. So, when I add an action button to my app, I’ll probably use a subclass so that the button can respond to the mouse click earlier.
Instead of subclassing, it's also possible to use -[NSControl sendActionOn:NSLeftMouseDownMask].