Kotlin Coroutines with Retrofit Not Returning Data

If you’re working with Kotlin Coroutines and Retrofit in Android development, encountering a situation where data is not returned from the API can be confusing. This article explores common causes and solutions to the issue: “Kotlin Coroutines with Retrofit Not Returning Data”. We’ll walk you through a simple working example, highlight key configurations, and help you debug this issue effectively.

Common Causes:

1. Network call is not awaited properly.
2. Retrofit service function returns Deferred<T> instead of suspend.
3. Coroutine scope misused or cancelled before receiving data.
4. Malformed JSON or improper error handling.

Retrofit and Coroutine Working Example

Let’s build a working example that demonstrates proper coroutine handling with Retrofit.

1. API Interface (RetrofitService.kt)

import retrofit2.http.GET

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

2. Model Class (Post.kt)

data class Post(
    val userId: Int,
    val id: Int,
    val title: String,
    val body: String
)

3. Retrofit Instance (RetrofitClient.kt)

import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory

object RetrofitClient {
    private const val BASE_URL = "https://jsonplaceholder.typicode.com/"

    val instance: RetrofitService by lazy {
        Retrofit.Builder()
            .baseUrl(BASE_URL)
            .addConverterFactory(GsonConverterFactory.create())
            .build()
            .create(RetrofitService::class.java)
    }
}

4. Repository (PostRepository.kt)

class PostRepository {
    suspend fun fetchPosts(): List<Post> {
        return RetrofitClient.instance.getPosts()
    }
}

5. ViewModel (PostViewModel.kt)

import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.launch

class PostViewModel : ViewModel() {

    private val repository = PostRepository()
    private val _posts = MutableStateFlow<List<Post>>(emptyList())
    val posts: StateFlow<List<Post>> = _posts

    init {
        getPosts()
    }

    private fun getPosts() {
        viewModelScope.launch {
            try {
                _posts.value = repository.fetchPosts()
            } catch (e: Exception) {
                e.printStackTrace()
            }
        }
    }
}

6. Activity (MainActivity.kt)

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.lifecycle.viewmodel.compose.viewModel

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            val postViewModel: PostViewModel = viewModel()
            // Observe postViewModel.posts here to show UI
        }
    }
}

🔍 Tips to Debug If Data Still Doesn’t Return

• Check internet permissions in AndroidManifest.xml.
• Use a tool like Charles Proxy to inspect API calls.
• Wrap network calls with try-catch to handle errors gracefully.
• Ensure that your CoroutineScope (e.g., viewModelScope) is active during execution.

This complete setup should eliminate the issue of Retrofit not returning data when using Kotlin Coroutines. Always double-check that you’re not mixing up suspend and Deferred, and keep an eye on coroutine lifecycles to avoid silent cancellations.