I'm not sure how WHEN helps me. How does WHEN give me the reference to the control 'passing' the focus? Could you further explain?

Is it possible to add the property to my navbutton class instead of the form to hold the object reference? I want to try to keep my classes as self contained and reliant as possible. If so, would this work?
Thisform.(This.LastObjFocus).SetFocus
Where This.LastObjFocus is the property and set to the name of the last object with focus provided by WHEN.
If my syntax is ridiculous above, please excuse me. I get a little lost in dot notations especially in combination with (), m., and & usage. Thanks