Inbox Message functionality allows you to send alerts with an inbox message or just an inbox message.
All inbox-only messages downloaded from Marketing Cloud are available via the InboxMessageManager. The SDK downloads new messages to InboxMessageManager each time your app comes into the foreground.
Use the methods in InboxMessageManager to implement a UI in your app to view inbox messages downloaded to the device. The methods that retrieve Inbox messages return only currently active messages. Reference the javadocs for more information.