Retrofit2 Coroutines CallAdapter

Sample Android application that show how can we create our own Retrofit CallAdapter for Coroutines to handle response as states.

Implementation

By creating your own CallAdapter, you can do the following:

interface Service {
    @GET("movies/{id}")
    suspend fun getMovie(): NetworkResponse<Movie, MovieError>
}

class Repository {
    val movie = service.getMovie()
    
    when (movie) {
        is NetworkResponse.Success -> // Success response
        is NetworkResponse.ApiError -> // Failure response (non-2xx)
        is NetworkResponse.NetworkError -> // Network failure
        is NetworkResponse.UnknownError -> // Unexpected exceptions
    }
}

The implementation of CallAdapter in the application is defined through the following classes:

• NetworkResponse - Sealed class that represents the API call response states.
• NetworkResponseCall - Call interface implementation.
• NetworkResponseAdapter - CallAdapter interface implementation.
• NetworkResponseAdapterFactory - CallAdapter.Factory abstract class implementation.

Also you need to make Retrofit aware of our custom CallAdapter.Factory:

fun provideRetrofit(okHttpClient: OkHttpClient): Retrofit {
    return Retrofit.Builder()
        .baseUrl(BASE_URL)
        .client(okHttpClient)
        .addCallAdapterFactory(NetworkResponseAdapterFactory())
        .addConverterFactory(GsonConverterFactory.create())
        .build()
}

Architecture

This sample application uses Architecture Components to separate the UI code in MainActivity from the application logic in MainViewModel. MovieRepository (and its concrete MovieRepositoryImpl implementation) provides a bridge between the ViewModel and MovieService, which uses Retrofit to return a list of Movie objects.

Libraries

• Kotlin + Coroutines
• Jetpack
  • ViewModel
  • LiveData
• Retrofit2
• OkHttp3
• Koin
• Timber
• MockK

Usage

To use this sample application you need to register your own TMDb API key and add it to the file NetworkModule.kt:

const val API_KEY = "INSERT-API-KEY-HERE"

References

• Create Retrofit CallAdapter for Coroutines to handle response as states