I have a navigation bar with buttons which I would like to share between multiple activities:

Currently, when I start the same activity (for example, click on LOST.DIR) the whole screen changes, including the navigation bar (new list of folders appears).
I would like to keep the navigation bar static (to persist between same activity types and not to change or re appear after starting a new activity).
Is this possible?
It sounds like you want to use one activity and fragments.
But, if you really must use multiple activities. Another approach would be to use an actionbar, (actionbarsherlock is great for this) and have the menu switch between your different activities. The menu drop down can either be a list of icons on the action bar or a drop down spinner located in the top right of the actionbar. This actionbar will be static throughout your activities and consist of the same list of categories (i.e. the ones of your navigation bar).