What is the lifecycle of an activity?

The Activity lifecycle refers to the entire process of an Activity from creation to destruction. In an Android application, each Activity goes through its own lifecycle, which includes several stages.

1. Initialization Stage: When an Activity is created, the system will call its onCreate() method to perform initialization operations, such as setting up the layout, binding data, and so on.
2. During the visible stage, the system invokes the onStart() method of the Activity when it becomes visible to the user, followed by the onResume() method. The Activity is able to interact with the user at this stage.
3. Pause phase: When another Activity covers the current Activity, the current Activity will enter a pause state. The system will call its onPause() method, during which temporary data can be saved or resources can be released.
4. Stop phase: When an Activity is completely obscured by another Activity, the system will call its onStop() method. During this phase, the Activity still remains in memory but is no longer visible to the user.
5. When an Activity transitions from the stopped state back to the visible state, the system will call its onRestart() method, followed by onStart() and onResume() methods.
6. Destruction Phase: When an Activity is destroyed, the system will call its onDestroy() method, allowing for the release of resources and cleanup work to be done.

It is important to note that the system may automatically destroy stopped activities based on memory conditions to release resources. When users return to a destroyed activity, the system will recreate it and restore it to its previous state.