What is the purpose of the onDestroy method in Android?

onDestroy() is the final callback method in the Activity lifecycle, used to release resources occupied by the activity and perform final cleanup tasks. When an Activity is destroyed, the system will call the onDestroy() method.

The onDestroy() method is usually used to perform the following actions:

1. Release resources: close database connection, unregister broadcast receivers, stop network connections, etc.
2. Cancel asynchronous tasks: Stop any ongoing asynchronous tasks to prevent memory leaks.
3. Save data: Save any unsaved data from the Activity to permanent storage media (such as a database or file) so that it can be restored when the Activity is created again in the future.
4. Perform cleanup operations: Remove temporary files and caches used in the Activity.

It is important to note that onDestroy() method is not always called when an Activity is destroyed. The system may destroy a background Activity to free up memory resources when the system is low on memory, triggering the onDestroy() method. Additionally, manually closing an Activity by pressing the back button will also trigger the onDestroy() method to be executed.