In this learning journey you will learn about the Cinemax app architecture: its layers, key classes and the interactions between them.
The goals for the app architecture are:
- Follow the official architecture guidance as closely as possible.
- Easy for developers to understand, nothing too experimental.
- Support multiple developers working on the same codebase.
- Facilitate local and instrumented tests, both on the developer’s machine and using Continuous Integration (CI).
- Minimize build times.
The app architecture has three layers: a UI layer, a data layer and a domain layer.
The architecture follows a reactive programming model with unidirectional data flow. With the data layer at the bottom, the key concepts are:
- Higher layers react to changes in lower layers.
- Events flow down.
- Data flows up.
The data flow is achieved using streams, implemented using Kotlin Flows.
The data layer is implemented as an offline-first source of app data and business logic. It is the source of truth for all data in the app.
Data is exposed as data streams. This means each client of the repository must be prepared to react to data changes.
To write data, the repository provides suspend functions. It is up to the caller to ensure that their execution is suitably scoped.
A repository may depend on one or more data sources. For example, the MovieRepositoryImpl
depends on the following data sources:
| Name | Backed by | Purpose |
| MovieDatabaseDataSource | Room/SQLite | Persistent relational data associated with Movies. |
| MovieNetworkDataSource | Remote API accessed using Retrofit | Data for movies, provided through REST API endpoints as JSON. |
Each repository has its own models. For example, the MovieRepository has a MovieModel model and
the TvShowRepository has a TvShowModel model.
Each repository method has its own use case. For example, the GetMoviesUseCase and
the GetTvShowsUseCase.
Use cases are the public API for other layers, they provide the only way to access the app data. The use cases typically offer one or more methods for reading and writing data.
The UI layer comprises:
- UI elements built using Jetpack Compose
- Android ViewModels
The ViewModels receive streams of data from repositories and transform them into UI state. The UI elements reflect this state, and provide ways for the user to interact with the app. These interactions are passed as events to the view model where they are processed.
UI state is modeled as a sealed hierarchy using interfaces and immutable data classes. State objects are only ever emitted through the transform of data streams. This approach ensures that:
- the UI state always represents the underlying app data - the app data is the source-of-truth.
- the UI elements handle all possible states.
View models receive streams of data as cold flows from one or more use cases. These are collected and the view model updates the corresponding UI state.
User actions are communicated from UI elements to view models using regular method invocations. These methods are passed to the UI elements as lambda expressions.