MVP pattern Android duplicated methods in presenters

Question

I have a couple activities, while each of them is rather unique, there has to be some common api calls like getCurrentUser() or updateUser()

Given the MVP pattern (I am currently using MVP mosby), since each of these activity only has a single presenter. As i am developing, it seems that sometimes I copy-paste a lot of these common api calls all over these presenters. Say I have api Call A, B, C, D.

A, C are used in presenter 1,

B, D, A are used in presenter 2,

C, E are used in presenter 3 .....

and so on. It is really difficult to find a "common" presenter to inherit from. So the api calls, C and A are basically copy pasted.

My question is, given the current situation, what is the best way to avoid code copy-pasting? Is it almost not avoidable? Or should I try my best to do OOP but risking a bunch of refactoring every time API calls are added/removed from different presenters?

Answer 1

You should decouple your common API and presenter code by putting all the API calls inside one or multiple Java classes that can be referenced from any presenter.

Therefore. ServiceA exists (A Java Class).

ServiceA performs API calls A,B,C,D.

Service A can be called from Presenter1, Presenter2, PresenterN, PresenterN+1. It should not matter what the presenter is.

If you want to restrict certain Presenters from having access to different API calls. Then this is when you should consider having ServiceA, ServiceB, ServiceC. Where ServiceA can only make API call A and D, Service B and Service C behave similarly.

Decoupling your Presenter code and common(Web Service, internal API, w/e code) will allow you to scale without having to do copy and paste.

Good luck.

Answer 2

I think you are risking more refactoring if you don't do it the OOP style, with inheritance. Let's say you want to modify the way you handle some api call. If you are copying code, you'll have to refactor everywhere you copied the code in the first place. If you inherit from a common presenter, you can just modify once.

Answer 3

You should make interface for your API that contains all your API requests. Then make singleton class that execute these requests, and you can easily access this class from your presenters.

Now you will still have some duplication and you will need to call this singleton multiple times in presenter and handle response in each of them, but that's what you need to do. Every presenter should be able to handle response different way, so you can't just pack them as one (even they will usually handle it the same way - by passing data to view).

If you think that you are writing a lot of similar code that does nothing, well that what you get with MVP. You also get great testing ability, easier refactoring and easy mock of requests - you could swap your real singleton for mock that implements same interface and everything works.

Answer 4

Interactor pattern (use case pattern) can solve your current issue of duplicating code.

The idea is that you extract all logic behind getCurrentUser() and updateUser() methods into a class (interactor) and use this interactor inside multiple presenters.

This is a very simplified explanation. I suggest you do more research starting with this post and this post for example.