actionBar
abstract fun actionBar(id: Int?, title: String?, actionBarContainerView: ViewGroup, actionBarView: ViewGroup): Single<ActionBarProvider.ExtraContents>?
Called when a view is ready to draw an action bar.
The id parameter is non-null for top level views, while the title parameter is for subsequent views in the navigation hierarchy. actionBarContainerView is the main container view for the action bar view, and includes some padding if the top tab bar is used. The action bar itself should be drawn into actionBarView.
Optionally returns a Single containing additional contents that can be handled in part by Book Library UI, such as a miniplayer view attached to the top bar.