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Very few Android apps today consist of just a single screen. In reality, most apps comprise multiple screens through which the user navigates using screen gestures, button clicks and menu selections. Prior to the introduction of Android Jetpack, the implementation of navigation within an app was largely a manual coding process with no easy way to view and organize potentially complex navigation paths. This situation has improved considerably, however, with the introduction of the Android Navigation Architecture Component combined with support for navigation graphs in Android Studio.

Every app has a home screen that appears after the app has launched and after any splash screen has appeared (a splash screen being the app branding screen that appears temporarily while the app loads). From this home screen, the user will typically perform tasks that will result in other screens appearing. These screens will usually take the form of other activities and fragments within the app. A messaging app, for example, might have a home screen listing current messages from which the user can navigate to either another screen to access a contact list or to a settings screen. The contacts list screen, in turn, might allow the user to navigate to other screens where new users can be added or existing contacts updated. Graphically, the app’s navigation graph might be represented as shown in Figure 38-1:

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