pietmau / Currencies

MVVM

• The View (CurrenciesFragment) binds to RxCurrenciesViewModel via LiveData.

• The ViewModel communicates with the UseCase (RxGetCurrenciesUseCase) via RxJava.

The reason of this mixture is that it would be interesting to implement the ViewModel with Coroutines (TODO). Having the presentation not relying on RxJava would allow us to do so.

The UseCase (RxGetCurrenciesUseCase)

Based on RxJava.

Every second it queries the repository with the symbol of the currency received from the user.

It implements retry.

It is retained across config changes via ViewModel (Architecture Components).

Modularity & Clean Architecture

The project is composed of three modules:

• Presentation (Android application)
• Data (Android Library)
• Domain (Java library)

Presentation depends on Data and Domain (transitively via Data)

Data depends on Domain

Domain does not depend on any other module.

Tests

There are unit tests (Junit 5) and Espresso tests in the respective directories:

• some unit tests in all modules, in the respective directories;
• some Espresso test in presentation

Dagger & Tests

In order to run the Espresso test, we inject a TestAppComponent that provides the test dependencies.

The RecyclerView

The CurrenciesRecycler uses DiffUtils and Payloads to update the rows efficiently.

Other libraries

• Mockk
• ViewModel
• LiveData
• LeakCanary
• Retrofit
• Dagger
• AndroidX

Currency

Money is represented with BigDecimal.

TODO

• Explain things a bit better (especially around RxJava).
• Use coroutines instead or RxJava.
• Use a bound service to get the rates.
• Repository is not really the right name, should find something better.
• Use a retrofit converter.
• Add a few more tests.