Most of us already know principles of Clean Architecture But to me these principles are more theoretical than practical. If we follow this principles directly we'll have about 6-9 classes for each screen (model, view, presenter, interactor, router, repository and so on).
- You can test only presenters and they are in fact very small piece of code in this architecture and don't cover all your sensitive logic
- More classes in your app - harder to understand where to write your code. When we have only view and presenter - this is obvious.
These are the main reasons, why we should consider another ways.
- Model is our POJO from server
- View is Activity or Fragment which interacts with the user and display all information
- Presenter is our most important object, which handles all business logic, handles lifecycle and manipulates view. Presenter uses repository to get data from the server or database.
- Repository is main layer between network and presenter
- Sends requests directly to the remote API
- Handles response, saves it to persistent storage and delivers to the presenter
- Handles server error and trying to fix them (such as session expired) or deliver to the presenter in more readable way
In this architecutre presenter covers all the business logic and it's the only thing we need to test.
We should be able to mock repository using DI principles, e.g. static field and setter or Dagger2.
Many developers believe that in MVP Presenter should be absolutely free from any Android dependencies in order to test it. I don't think so. Using something like Mockito could solve all these dependencies without a great efforts from developer.
So, our final architecture will look like this:
In this repository you can find samples for the described model. If you're new to Android Architecture, I suggest you to check the PopularMovies project, since it's very simple and easy to understand.
If you're looking for more complicated architecture take a look at StackExchangeClient. It's rather large sample, with many screens and more - all presenters are tested with 100% coverage!
MVVM for Android became more possible after release of DataBinding. Google also suggest architecture variant with DataBinding< but again - it's very complicated and doesn't make sense.
The only variant when MVVM is acceptable is this architecture:
This architecture was implemented in PopularMoviesDataBinding sample. You can take a look on it and decide for yourself - is it good or not :) Personally I believe that MVP is much better.