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Introduction to Retrofit in Android

Introduction to Retrofit in Kotlin Android

Retrofit is a type-safe HTTP client for Android and Java. It simplifies the process of making network requests and handling the response data. With Retrofit, you can define and send HTTP requests using simple annotations and convert the response to a desired format, like JSON or XML.

In this tutorial, we will explore the features of Retrofit and learn how to install and use it in a Kotlin Android project.

Features of Retrofit​

Retrofit comes with a range of features that make it a popular choice for networking in Android applications. Some of the key features include:

  1. Retrofit Annotations: Retrofit provides a set of annotations that can be used to define the structure of network requests. These annotations include @GET, @POST, @PUT, @DELETE, etc.

  2. Automatic JSON/XML Parsing: Retrofit can automatically convert the response data into Java/Kotlin objects using various converters like Gson, Moshi, or Jackson. This eliminates the need for manual parsing of JSON/XML data.

  3. Request Interceptors: Retrofit allows you to intercept and modify requests at runtime using interceptors. This can be useful for adding headers, logging, or authentication.

  4. URL Manipulation: Retrofit supports dynamic URL manipulation, allowing you to pass dynamic parameters in the URL.

  5. Synchronous and Asynchronous Requests: Retrofit supports both synchronous and asynchronous network requests. You can choose the appropriate method based on your requirements.

  6. Error Handling: Retrofit provides built-in error handling mechanisms, such as defining error models and handling different HTTP status codes.

Installation​

To use Retrofit in your Kotlin Android project, follow these steps:

  1. Add the Retrofit dependency to your project's build.gradle file:
dependencies {
    implementation 'com.squareup.retrofit2:retrofit:2.9.0'
    implementation 'com.squareup.retrofit2:converter-gson:2.9.0' // Replace with your preferred JSON converter
}
  1. Sync your project to download the Retrofit library.

Usage of Retrofit​

Now that we have Retrofit installed, let's see how to use it in our Kotlin Android project.

  1. Create a data class to represent the response data:
data class User(
    val id: Int,
    val name: String,
    val email: String
)
  1. Define an interface for the API endpoints:
interface ApiService {
    @GET("users")
    suspend fun getUsers(): List<User>
}
  1. Create a Retrofit instance and build the API service:
val retrofit = Retrofit.Builder()
    .baseUrl("https://api.example.com/") // Replace with your API base URL
    .addConverterFactory(GsonConverterFactory.create()) // Replace with your preferred JSON converter
    .build()

val apiService = retrofit.create(ApiService::class.java)
  1. Make a network request using the API service:
val users = apiService.getUsers()

In the above example, we are making a GET request to the /users endpoint and receiving a list of User objects as the response.

Note: The suspend keyword is used to make the network request asynchronously. If you want to make synchronous requests, replace suspend with Call and use enqueue instead of await.

Retrofit Examples​

Here are more Retrofit examples: