This is going to be messy, so step by step: Imagine that you are developing an add-in that uses a temporary user interface (not permanent one) , and creates a couple of commandbars of kind "toolbar", and many commandbars of kind "popup" (with submenus). Since it uses a temporary user interface, it must delete those commandbars when unloaded. For that purpose, it must keep a reference to each created commandbar at class level (all this is explained in the article of the previous