Introduction to Retrofit

As we already mentioned, Retrofit is an open source library. It is the most popular HTTP client for Android used today. Because of that, we will introduce you to Retrofit basics and demonstrate how to use it. The version we will cover is 2.3.0. We will give you step-by-step guidance on how to use it.

First of all, Retrofit depends on some libraries too. We will use it with Okhttp. Okhttp is an HTTP/HTTP2 client developed by the same guys who developed Retrofit. Before we start, we will put dependencies into our build.gradle configuration as follows:

    apply plugin: "com.android.application" 
    apply plugin: "kotlin-android" 
    apply plugin: "kotlin-android-extensions" 
    ... 
    dependencies { 
      ... 
      compile 'com.squareup.retrofit2:retrofit:2.3.0' 
      compile 'com.squareup.retrofit2:converter-gson:2.0.2' 
      compile 'com.squareup.okhttp3:okhttp:3.9.0' 
      compile 'com.squareup.okhttp3:logging-interceptor:3.9.0' 
   } 

We updated our Retrofit and Okhttp to the latest version. We added dependencies for the following:

• Retrofit library
• Gson converter that will be used to deserialize the API responses
• Okhttp library
• Logging interceptor for Okhttp so we can log what is going on with our API calls

After we synchronize our Gradle configuration, we are ready to start!