These are the two options when thinking about the bottom navigation for an Android App. What are the use cases for both? When should one be used over the other?
That certainly depends on the how the information architecture is - categorization of information hierarchy.
Bottom Navigation is mainly used to navigate between primary destinations in the app. From the above example, the primary navigational tasks - which the user will most often make - is to move between home, messages, and info.
Bottom App bar, however, is used to navigate between different sections in the app. For example, the app bar could also include navigation drawer and action buttons.
The main difference I could give for the two is, bottom app bar can be used on screens to provide convenient access to actions (at least more than one) - can be considered action driven tasks, whereas bottom navigation can be used on screens to provide convenient access to navigation (mainly primary movements).
As they are in the bottom, which is easily accessible distance for fingers, it is important that you use the area efficiently and include the most important actions or navigation for the app.
Bottom app bars provide access to more actions, including a FAB. Bottom navigation bars display destinations. Bottom app bars focus on actions while bottom navigation bars focus on navigation to top-level destinations that need to be accessible from anywhere in the app.
And they have two obvious differences:
- Bottom navigation should be used for 3 to 5 destinations, and bottom app bars should be used for 3 to 6 actions (count FAB);
- Bottom navigation can be used for mobile or tablet, and bottom app bars only be used for mobile devices.