title: rails pass instance variable to layout or local variable
body: <p>I have a navigation bar (in fact two) and I use a before action in some controllers to fill it's dynamic data (the second bar may not exist in some), I've seen a lot of complains about not passing a lot of instance variables to views, and all of them suggested passing locals in render. I've been wondering using a instance variable to generate these stuff in the main layout is a good idea or not, and if it's not, how should I do this, render seems to overwrite the default view and I use the data in the main layout only</p>