actionBar

Called when a view is ready to draw an action bar.

fragment is used to identify which view is associated with the 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.

actionBarContainerView may already be android.view.View.GONE when this is called for a root view whose action bar is suppressed via UiHelpers.isRootViewInHostHierarchy. In that case the implementation should still process id/title/extras to determine the config it would have shown, so the host can surface it elsewhere, but should not attempt to draw into the (invisible) view.