Android's Action Bar visiblity

Question

I need advice regarding Android's action bar usage. Do you think an action bar should always:

a) remain visible on all screens of an application (except when the user choose to view for example a video in full screen)

or

b) invisible on certain screens and visible only on suitable screen for example, a list with description, etc.

Answer 1

If you're talking about Action Bar, I presume you're designing for Ice Cream Sandwich. In that case, let's take a look at what Android Design Guide have to say about it:

The action bar is arguably the most important structural element of an Android app. It's a dedicated piece of real estate at the top of each screen that is generally persistent throughout the app.

This means that unless there's a contextual need or something needs to be viewed in full screen mode (like a video), the Action Bar should be visible. By function, you can think of it as iOS's Tab Bar joined with the Toolbar because Action Bar merges navigation and actions into one control element.