In this tutorial we will learn how to implement Retrofit HTTP client in Android with Kotlin.
Retrofit is a powerful HTTP client for an Android and Java built by awesome folks at Square . Retrofit Configured with convertors makes it easy to serialize structured data sets. Typically for JSON we uses Gson convertors to serialization and De-serialization process.
Retrofit uses the Okhttp library for for HTTP requests.
Please find the sample project given below.
- Open your project and add dependencies into app level build.gradle ( Module:app) file. Here we adds Gson,RecyclerView,CardView,Piccasso and Retrofit libraries
dependencies {
...
implementation 'com.google.code.gson:gson:2.8.4'
implementation 'com.squareup.retrofit2:retrofit:2.3.0'
implementation 'com.squareup.retrofit2:converter-gson:2.3.0'
implementation 'com.squareup.okhttp3:logging-interceptor:3.8.0'
implementation "com.android.support:cardview-v7:27.1.1"
implementation 'com.android.support:recyclerview-v7:27.1.1'
implementation 'com.squareup.picasso:picasso:2.71828'
...
}- Make sure you have added the INTERNET permission in AndroidManifest.xml file like this.
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="kotlincodes.com.retrofitwithkotlin">
<uses-permission android:name="android.permission.INTERNET"/>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".activity.MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>- Next we need to create data model to parse our sample Json response . The sample response is given below.
- Now Create a Kotlin Class named DataModel.kt under model package like shown below.
DataModel.kt
package kotlincodes.com.retrofitwithkotlin.model
import com.google.gson.annotations.Expose
import com.google.gson.annotations.SerializedName
data class DataModel(
@Expose
@SerializedName("albumId")
val albumid: Integer,
@Expose
@SerializedName("id")
val id: Integer,
@Expose
@SerializedName("title")
val title: String,
@Expose
@SerializedName("url")
val url: String,
@Expose
@SerializedName("thumbnailUrl")
val thumbnailurl: String
)- Now create a retrofit instance to make a network request to a REST API with Retrofit.
- Here we creates a Kotlin object ApiClient.kt under retrofit package.
- The BASE_URL is the basic URL of your API where we will make a call
ApiClient.kt
import com.google.gson.GsonBuilder
import okhttp3.OkHttpClient
import okhttp3.logging.HttpLoggingInterceptor
import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory
object ApiClient {
var BASE_URL:String="https://jsonplaceholder.typicode.com/"
val getClient: ApiInterface
get() {
val gson = GsonBuilder()
.setLenient()
.create()
val interceptor = HttpLoggingInterceptor()
interceptor.setLevel(HttpLoggingInterceptor.Level.BODY)
val client = OkHttpClient.Builder().addInterceptor(interceptor).build()
val retrofit = Retrofit.Builder()
.baseUrl(BASE_URL)
.client(client)
.addConverterFactory(GsonConverterFactory.create(gson))
.build()
return retrofit.create(ApiInterface::class.java)
}
}
- Define End Points : Now we create an interface ApiInterface.kt under retrofit package to define the api end points
ApiInterface.kt
import kotlincodes.com.retrofitwithkotlin.model.DataModel
import retrofit2.Call
import retrofit2.http.GET
interface ApiInterface {
@GET("photos")
fun getPhotos(): Call<List<DataModel>>
}
- Set up MainActivity Class
- Now we are all set to make an api call in MainActivity.kt .
- getData() method is used to make HTTP request using Retrofit
- Here we fetch data and populate it in to a RecyclerView , the RecyclerViewAdapter DataAdapter and RecyclerView layouts are described later.
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".activity.MainActivity">
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="wrap_content">
</android.support.v7.widget.RecyclerView>
</android.support.constraint.ConstraintLayout>MainActivity.kt
class MainActivity : AppCompatActivity() {
lateinit var progerssProgressDialog: ProgressDialog
var dataList = ArrayList<DataModel>()
lateinit var recyclerView: RecyclerView
lateinit var adapter:DataAdpter
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
recyclerView = findViewById(R.id.recycler_view)
//setting up the adapter
recyclerView.adapter= DataAdpter(dataList,this)
recyclerView.layoutManager=LinearLayoutManager(this,LinearLayoutManager.VERTICAL,false)
progerssProgressDialog=ProgressDialog(this)
progerssProgressDialog.setTitle("Loading")
progerssProgressDialog.setCancelable(false)
progerssProgressDialog.show()
getData()
}
private fun getData() {
val call: Call<List<DataModel>> = ApiClient.getClient.getPhotos()
call.enqueue(object : Callback<List<DataModel>> {
override fun onResponse(call: Call<List<DataModel>>?, response: Response<List<DataModel>>?) {
progerssProgressDialog.dismiss()
dataList.addAll(response!!.body()!!)
recyclerView.adapter.notifyDataSetChanged()
}
override fun onFailure(call: Call<List<DataModel>>?, t: Throwable?) {
progerssProgressDialog.dismiss()
}
})
}
}
- Set up RecyclerView
- To set up RecyclerView we need a list layout and RecyclerView.Adapter DataAdapter.kt as given below.
- The layout includes only a text view to show the title.
list_item_home.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_margin="6dp"
app:contentPadding="12dp"
android:layout_height="wrap_content">
<TextView
android:maxLines="1"
android:id="@+id/title"
android:layout_gravity="center"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</android.support.v7.widget.CardView>DataAdapter.kt
package kotlincodes.com.retrofitwithkotlin.adapters
import android.content.Context
import android.support.v7.widget.RecyclerView
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import kotlincodes.com.retrofitwithkotlin.R
import kotlincodes.com.retrofitwithkotlin.model.DataModel
class DataAdpter(private var dataList: List<DataModel>, private val context: Context) : RecyclerView.Adapter<DataAdpter.ViewHolder>() {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
return ViewHolder(LayoutInflater.from(context).inflate(R.layout.list_item_home, parent, false))
}
override fun getItemCount(): Int {
return dataList.size
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
val dataModel=dataList.get(position)
holder.titleTextView.text=dataModel.title
}
class ViewHolder(itemLayoutView: View) : RecyclerView.ViewHolder(itemLayoutView) {
lateinit var titleTextView:TextView
init {
titleTextView=itemLayoutView.findViewById(R.id.title)
}
}
}
Now we are all done. We have
kotlincodes/Retrofit-With-Kotlin
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