Retrofit with Kotlin Jetpack Compose, Clean Architecture, and MVVM

Retrofit is a popular library for making network requests in Android apps. With the rise of Kotlin and Jetpack Compose, it’s important to know how to use Retrofit in these new technologies. In this article, we’ll show you how to use Retrofit with Kotlin and Jetpack Compose while following the Clean Architecture pattern.

Clean Architecture is a software design pattern that separates the concerns of an app into layers. This pattern allows for easier testing, maintainability, and scalability. In Clean Architecture, there are three main layers: Domain, Data, and Presentation.

1. The Domain Layer is the core of the app and contains the business logic. This layer should not be dependent on any other layer and should not know about the implementation details of the other layers.
2. The Data Layer is responsible for providing data to the Domain Layer. This layer communicates with external sources such as the network or a local database.
3. The Presentation Layer is responsible for displaying data to the user. In Android apps, this layer is often implemented using a UI framework such as Jetpack Compose.

Now, let’s see how we can use Retrofit with Kotlin and Jetpack Compose while following the Clean Architecture pattern.

The example used in the code is a simple blog post application.

The Post data class represents a blog post with the following properties: id, title, body, and userId. The app retrieves a list of posts from an API and displays them in a list using Jetpack Compose.

First, we need to create a Retrofit client in the Data Layer. Here’s an example of how to create a Retrofit client using the Retrofit.Builder:

val retrofit = Retrofit.Builder()
    .baseUrl(BASE_URL)
    .addConverterFactory(GsonConverterFactory.create())
    .build()

val apiService = retrofit.create(ApiService::class.java)

Next, we need to create an interface that defines the API endpoints. Here’s an example of an interface that defines a GET request:

interface ApiService {
    @GET("/posts")
    suspend fun getPosts(): List<Post>
}

We can now use this interface to make network requests in the Data Layer. Here’s an example of how to make a GET request using Retrofit:

class PostRepository(private val apiService: ApiService) {
    suspend fun getPosts(): List<Post> {
        return apiService.getPosts()
    }
}

Now that we have the Data Layer set up, we can move on to the Presentation Layer. In this example, we’ll be using Jetpack Compose to display the data to the user. Here’s an example of how to create a Composable function that displays a list of posts:

@Composable
fun PostList(posts: List<Post>) {
    LazyColumn {
        items(posts) { post ->
            Text(text = post.title)
        }
    }
}

Finally, we need to connect the Presentation Layer to the Data Layer using the Domain Layer. Here’s an example of how to create a use case in the Domain Layer that retrieves the list of posts:

class GetPostsUseCase(private val postRepository: PostRepository) {
    suspend operator fun invoke(): List<Post> {
        return postRepository.getPosts()
    }
}

We can now use this use case in the Presentation Layer to retrieve the list of posts and display them to the user. Here’s an example of how to do this using a ViewModel and the rememberCoroutineScope function:

@Composable
fun PostScreen(viewModel: PostViewModel) {
    val scope = rememberCoroutineScope()

    LaunchedEffect(Unit) {
        scope.launch {
            viewModel.getPosts()
        }
    }

    val posts by viewModel.posts.collectAsState()

    PostList(posts)
}

class PostViewModel(private val getPostsUseCase: GetPostsUseCase) : ViewModel() {
    private val _posts = MutableStateFlow(emptyList<Post>())
    val posts: StateFlow<List<Post>> = _posts

    suspend fun getPosts() {
        _posts.value = getPostsUseCase()
    }
}

We can now create an instance of this ViewModel in our Composable function and pass it to the PostScreen function:

@Composable
fun MyApp() {
    val postRepository = PostRepository(apiService)
    val getPostsUseCase = GetPostsUseCase(postRepository)
    val viewModel = PostViewModel(getPostsUseCase)

    MaterialTheme {
        PostScreen(viewModel = viewModel)
    }
}

And that’s it! We have successfully used Retrofit with Kotlin and Jetpack Compose while following the Clean Architecture pattern. This allows for easy testing, maintainability, and scalability of our app.

In conclusion, Retrofit is a powerful library for making network requests in Android apps. When combined with Kotlin and Jetpack Compose, it can be used to create scalable, maintainable, and testable apps while following the Clean Architecture pattern. By following this pattern, we can separate the concerns of our app into layers, making it easier to maintain and test our code.