What role an Android Service should play in the MVP pattern?

Question

I am developing an Android app that does Human Activity Recognition.

It basically works like that - Service constantly reads the accelerator data and stores the recognized activity (ie Walking, running) in a database. The user can see all of the recognized activities in an ListView in activity (accesses the database). Every User table in the database has a pa_goal (physical activity goal) field which the Service reads from the database and does some checks.

The user, of course, can change this goal from an activity. Since I will be implementing the MVP architectural pattern.

I am unsure where to put the Service? It surely isn't View. Any advice?

Answer 1

In a clean architecture, which is what I am assuming you are using MVP for, there is the idea of separating the framework from the business logic. This is essentially what a normal presenter allows you to do.

In this case its not a view you are dealing with but the principle is similar. You don't want all your business or application logic mixed in the Android code when you can separate them out for nicer, more single responsibility classes. So I would say that while it isn't a view you should still have a presenter type class (probably better to be called controller or manager maybe).

This class would be a POJO that controls how your service behaves which is easily testable with standard junit tests and service mocks. This class and the service could then be put into its own feature package and interact with the back end models the same way as your presenters.

So, in summary, the role is of another feature of your app that sites alongside the other features (which are usually just views in my experience).

Hope that helps

Answer 2

This article helped me in a similar situation, although may not be exactly yours, the idea is the same:

https://android.jlelse.eu/android-bound-services-and-mvp-12ca9f70c7c7

Basically, the author works around the fact that a bound service is tightly coupled to an activity, and it adds extra lifecycle calls to it.

Answer 3

I am in the same situation. Finally I decided to do something like this:

Activities or Fragments are out of scope, they do not know anything about MVP BUT i am going to use an event bus like Otto to send signals/events, So:

My classes which extends some kind of Presenter know nothing about Android Context but they will have an MvpView interface, with only onAttachPresenter and onDetachPresenter.

The class which extends Service will have a Presenter attribute and implements some MvpView interface with onSucess, onError, onStart, onComplete or something like that and same events for Otto (onSucessEvent, onErrorEvent, onStartEvent, onCompleteEvent).

So when I need to do something the Activity or Fragment will start the service, the service will "start" or talk with the Presenter and when the presenter finish with success will call to mvpView.onSuccess() and store the info inside a local DB with SQLite (storeIO maybe) and finally the Service will invoke Otto and pass the signal (without any data on it), probably onComplete. Finally the signal will be catched by my UI (fragment maybe) and retrieve all the info inside a DB in SQLite.

So when the onSucess happens the UI will show the latest and best data BUT when onError happens will (at least) show some info (or not if you want) saying to the user "there was a problem but at least you can see something", bot onSuccess and onError will call onComplete after all.

Do not know if this is the best solution but in this case I think I am not going to deal with Activities or Fragments lifecycle and do not care about onSaveInstance and restore data when the user rotates the device. It will always fetch the latest data inside DB, and if something happens (no internet connection) you can at least show something when you receive the onComplete Signal.

Some facts I am still thinking:

• The Presenter won't be a singleton class
• Presenter knows nothing about Context but yes with MyApplication class
• What happens if for one screen (Fragment) you have differents service with differents onSuccessEvents? Simply use some kind of action as an ID, to identify them.
• Never make the Activity Fragment implements the MvpView, you will have to deal with the lifecycle.