New Android App Architecture Prototype

[rtibbles]

Currently the architecture of the Android App takes can be summed up by this diagram:

It is proposed instead to shift the architecture of the app to this:

The main reasons for this are as follows:

• At the moment we use a permanent foreground service to persist the entire Kolibri stack.
  • This causes increased battery usage, and currently is very difficult for the user to quit without force quitting
  • While the persistent foreground service is not yet banned by updated Android versions, the direction of travel seems to be to try to limit the use of this anti-pattern to have things running in the foreground as much as possible: https://developer.android.com/about/versions/12/behavior-changes-12#foreground-service-launch-restrictions
  • Most elements of the Kolibri stack do not need to run continuously when the app is not in the foreground, so we should restrict ourselves to only keeping those things open
• There is current work in progress on Python for Android to allow for integration with the Android WorkManager API, this would allow us to defer asynchronous task processing to Android, this would allow us to:
  • Not run our worker handler and scheduler handler at all, and defer the starting of asynchronous tasks to the WorkManager API
  • Start activities in response to changes in network state, such as scanning the local network for other Kolibri devices when on a local network, but otherwise not bothering

In order to achieve this, the main things we need to accomplish are:

• Making the Kolibri Process Bus easier to subclass/pick and choose functionality, in order to make custom app architectures easier
• Simplifying the Kolibri task API to allow simple addition of hooks to that allow it to connect to the Android API
• Adding additional metadata to tasks indicating if they are expected to be 'long running'

[rtibbles]

This has been implemented and launched with 0.16.0.