Is Model-View-Presenter (MVP) scheme useful for Android?

Question

How to separate View and Presenter in Android, while the reactions on the user actions (Presenter part of MVP) are set into the same activities that shows GUI elements (View part of MVP).

"In model view presenter just as Martin Fowler or Michael Feathers [2] say, the logic of the UI is separated into a class called presenter, that handles all the input from the user and that tells the "dumb" view what and when to display" (cited from here).

Till now I thought that one of the main features of Android is the smart Activity that takes actions, reacts to them and shows the results. Is MVP scheme in contradiction with Android philosophy? Has it sense to try to realize it on Android? If yes, how could it be done?

Answer 1

Android applications are fundamentally built around Model-View-Controller (MVC) - MVP sounds like the same thing, although I've not heard the term before. Activities fill the role of Controller, XML Views are just that (although you can build them programmatically in the Activity - it's just easier and simpler to do it in XML), and the Model you write yourself. So yes, that model is quite practical.

A possible reason you may not have heard much about this design model is that the Android framework forces you to separate the view out. Because the application on mobile devices tend to be small, people don't tend to use full-on MVC; they tend toward view and action layers where the action layer does much of the model's (small) job.

If you are writing a cross platform app, you may want to look at a four-layer approach: View, Action, Business Logic, and Model. The View and Action layers would be platform specific, while the Business Logic and Model would not change. Basically, you split out the presenter and user interaction out to the Action layer, which calls the Business Logic layer to perform the action the user wants.

Answer 2

I don't have any experience on Android programming, but having a short look into some introductory Android programming tutorials I don't see a reason why MVP should be less useful as in any other event driven framework. The Activity class is not very different from the Dialogor Form in other frameworks, so it should be easy to create an "Activitity Presenter" class for any Activity subclass of your application and put the core logic there.

Events send to your "Activity" must be delegated to your presenter, and if your presenter is going to send events on its own, or call other system dependent features, your Activity must provide related functions via the interface it shares with the presenter. But that is basically the same as in any other GUI framework I know of.

Answer 3

MVP is definitely useful for Android. It helps to organise and unit test your code. And the best part is new people reading your code will be able to understand the code and will start contributing soon as they know what should go where. Here is a very helpful link to understand MVP with examples.

Here is a brief explanation of all the three components of MVP

View

In android MVP, a view contains two things Activity – android resource View – java interface Activity Implements the View and it injects itself(View interface) in the presenter so that presenter can talk to activity using view interface. First three blocks of the diagram shows the communication between View and The Presenter.

Presenter

Presenter acts as a middle layer between View and Data/Model. View(Activity) commands presenter to present something and presenter then takes data from the database/Model and gives back the presentable form of data to the View. View then takes care of displaying that data on the screen. And remember that Presenter is a plain java class it should not include any of the android components otherwise it will make the unit testing of the presenter hard.

If you wish to use database in the presenter then make activity create a database instance and inject it in the presenter. This will help you to mock the database while unit testing and will enable you to test the business logic.

Model

Model in MVP is nothing but your data source. View does not talk to data directly instead it commands Presenter to handle data for it and give the information back which can be displayed without any further modification.