Lesson 19: Making Network Requests: Introduction to Retrofit

Making Network Requests: Introduction to Retrofit

Time to fetch real data from an actual API instead of hardcoded lists. We'll use Retrofit, the standard networking library across the Android ecosystem.

Add the dependencies

implementation("com.squareup.retrofit2:retrofit:2.11.0")
implementation("com.squareup.retrofit2:converter-gson:2.11.0")
implementation("androidx.compose.runtime:runtime-livedata:1.7.0")

Declare your API endpoint

interface TaskApi {
    @GET("todos")
    suspend fun getTasks(): List
}

The suspend keyword marks this as a coroutine — Kotlin's way of running long operations (like a network call) without freezing the UI while waiting. We'll use suspend functions constantly from here on; for now, just know it means "this can take time, and won't block the app while it does."

Build the Retrofit instance

val retrofit = Retrofit.Builder()
    .baseUrl("https://jsonplaceholder.typicode.com/")
    .addConverterFactory(GsonConverterFactory.create())
    .build()

val taskApi = retrofit.create(TaskApi::class.java)

We're using JSONPlaceholder, a free fake API perfect for learning — no API key, no backend of your own required.

Calling it from a ViewModel

class TaskListViewModel : ViewModel() {
    var tasks by mutableStateOf>(emptyList())
        private set

    init {
        viewModelScope.launch {
            tasks = taskApi.getTasks()
        }
    }
}

viewModelScope.launch { } is how you call a suspend function from a ViewModel — it runs the network call in the background and automatically cancels it if the ViewModel is destroyed, so you never leak a request nobody's waiting for anymore.

Next: Lesson 20 — properly modeling the JSON data this API actually returns.