In a typical mobile application, the user can navigate from one destination to another. Each of these destinations can be regarded as a ‘screen’: a set of components that fulfill a very specific use case. For example, the main screen of a Twitter client may show a list of tweets to the user.

In Acorn these screens are represented by Scene objects¹. A Scene represents a destination in an application the user can navigate to. A Scene is usually a screen in your application, but may also be a dialog or even something entirely else. A single traditional 'screen' could perhaps even consist of two separate Scenes, for example when you enter an 'edit mode' for the screen.

A note on Scenes versus Activities or Fragments

In a sense, Scenes are similar to Activities or Fragments: when used as a primary navigational unit, they both represent a screen in an application.

A couple of key differences are:

• Scenes are not created by the system, but can accept dependencies in their constructors;
• Scenes only have one responsibility: connecting the UI to the business logic. They do not:
  • Create any views
  • Control application flow directly
  • Have system callbacks (like permissions)
• Scenes always survive configuration changes.

1: Note that Acorn's Scene objects are a completely different concept than Android's Scenes used for transitions.