How many items are required in bottomNavigationBar?
The length of items must be at least two and each item's icon and title/label must not be null.
What is bottom app bar?
com.google.android.material.bottomappbar.BottomAppBar. The Bottom App Bar is an extension of Toolbar that supports a shaped background that "cradles" an attached FloatingActionButton . A FAB is anchored to BottomAppBar by calling CoordinatorLayout.