An activity in Android is a fundamental application component that represents a single screen with which users can interact, similar to a window or frame in desktop applications
. It combines both the user interface design (defined in XML files) and the behavior or logic (implemented in Java or Kotlin files), making it a container for the app's UI and the code that controls it
. Each activity provides a window where the app draws its UI, usually filling the entire screen, and typically corresponds to one screen in an app, such as a login screen, home screen, or settings screen
. An Android app usually consists of multiple activities that work together but are loosely bound, allowing navigation between different screens or even launching activities from other apps
. The lifecycle of an activity is managed by the system through a series of
callback methods like onCreate(), onStart(), onResume(), etc., which
handle states such as creation, starting, resuming, pausing, stopping, and
destruction. This lifecycle management ensures that the activity behaves
correctly as the user interacts with the app or switches between apps
. Activities must be declared in the app's manifest file, which defines their attributes and how they are launched, often through intents that signal the system to start a particular activity based on user actions or other events
. In summary:
- An activity is a screen in an Android app, combining UI layout and code.
- It manages user interaction and app behavior on that screen.
- Activities have a lifecycle managed by callback methods.
- Multiple activities form the app’s user experience, and each must be declared in the manifest.
- Activities can start other activities within or outside the app.
This concept is central to Android app development, enabling modular, interactive, and navigable user interfaces
