activitynavigation

Activity navigation describes the methods by which an application transitions between screens, or activities, during user interaction. In platforms that use the activity metaphor—most notably Android—each activity encapsulates a discrete user interface and lifecycle. Navigation is coordinated through intents, the activity back stack, and task management.

Intents are messages that request the system to start another activity. They can be explicit—specifying the exact class to launch—or implicit, declaring a general action. Data can be passed via extras. When a new activity starts, it is pushed onto the task's back stack. The user can return to previous screens using the back button; the system resumes the prior activity in the stack.

Launch modes and intent flags influence how activities stack or reappear. Manifest attributes such as launchMode and flags like FLAG_ACTIVITY_CLEAR_TOP or NEW_TASK affect behavior, including whether an existing instance is reused or a new instance is created. Up navigation is the convention of moving to a logical parent screen, which may be implemented by the app's navigation structure rather than the system back stack.

To simplify and centralize navigation, modern development often employs a navigation component that defines a navigation graph of destinations and actions. This approach supports argument passing, deep linking, and consistent transitions. Some apps use a single-activity architecture with multiple fragments, using the navigation component to manage transitions within one activity.

Design considerations include consistency of back and Up behavior, proper lifecycle handling, accessibility, and testing of navigation flows. While activity navigation remains essential in many apps, contemporary patterns favor navigation libraries and component-based architectures to improve modularity and state management.