What is the ActivityThread in Android and the process of launching an app?

ActivityThread is the thread responsible for managing all Activities in Android, handling tasks such as managing Activity lifecycle, event dispatching, and message handling.

The process of launching the app is as follows:

1. When the user clicks on the app icon, the system will start the application process.
2. The system will create an ActivityThread object and call its attach method to associate the application’s Context object with the ActivityThread.
3. ActivityThread will create a Handler object and start processing messages in the message queue.
4. The ActivityThread will invoke the callApplicationOnCreate method of the Instrumentation object, triggering the app’s creation process.
5. The Application object will be created by the app and its onCreate method will be called to perform some initialization work.
6. ActivityThread will invoke the callActivityOnCreate method of the Instrumentation object to create the launch Activity of the application.
7. The lifecycle methods of the Activity will be invoked, including onCreate, onStart, onResume, etc.
8. The application has finished launching, allowing users to see the app interface and start interacting with it.