Kotlin - Retrofit Service - Method(Get) Android Studio Example

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In this example, I will show you how to call Retrofit service and display download data into RecyclerView. 

Kotlin Retrofit Service Example Video

  • You can also go through this video explanation.


Kotlin Retrofit Service Method(Get) Example

Creating a New Project

  • So first create a new Android Studio project using Kotlin.
  • Once the project is loaded come inside the activity_main.xml and remove the Hello World TextView.
Android studio project screen

JSON Service Url:
https://jsonplaceholder.typicode.com/posts

JSON service output screen:-



Step 1:
Open build.gradle and add following dependency and rebuild the project.
implementation 'com.squareup.retrofit2:retrofit:2.3.0'
implementation 'com.squareup.retrofit2:converter-gson:2.3.0'
implementation 'com.google.android.material:material:1.2.0'
implementation 'androidx.recyclerview:recyclerview:1.1.0'
implementation 'androidx.cardview:cardview:1.0.0'
Step 2:
Open AndroidManifest.xml and add Internet Permission.
<uses-permission android:name="android.permission.INTERNET"/>
Step 3:
Create new Package:- model
PostsDataModel.kt
Create new class PostsDataModel.kt under model package and Add following code.
package com.kotlinkatta.retrofitget.model

import com.google.gson.annotations.Expose
import com.google.gson.annotations.SerializedName

data class PostsDataModel(
    @Expose
    @SerializedName("userId")
    val userId: Integer,
    @Expose
    @SerializedName("id")
    val id: Integer,
    @Expose
    @SerializedName("title")
    val title: String,
    @Expose
    @SerializedName("body")
    val body: String
)
Step 4:
Create new Layout:- posts_data_row.xml
Create new posts_data_row.xml file under layout folder and Add following code.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <androidx.cardview.widget.CardView
        android:layout_margin="10dp"
        app:cardCornerRadius="5dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@color/colorAccent">

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_margin="3dp"
                android:padding="10dp"
                android:background="#ffffff"
                android:orientation="vertical">

                <TextView
                    android:id="@+id/txt_title"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:textColor="#000000"
                    android:justificationMode="inter_word"
                    android:textSize="18dp" />

                <TextView
                    android:layout_marginTop="3dp"
                    android:id="@+id/txt_body"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:justificationMode="inter_word"
                    android:textSize="20dp" />
             </LinearLayout>
        </LinearLayout>
    </androidx.cardview.widget.CardView>
</LinearLayout>
Step 5:
Create new Package:- adapter
PostsDataAdapter.kt
Create new class PostsDataAdapter.kt under adapter package and Add following code.
package com.kotlinkatta.retrofitget.adapter

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView
import com.kotlinkatta.retrofitget.R
import com.kotlinkatta.retrofitget.model.PostsDataModel
import kotlinx.android.synthetic.main.posts_data_row.view.*

class PostsDataAdapter (val userList: List<PostsDataModel>) : RecyclerView.Adapter<PostsDataAdapter.ViewHolder>() {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val v = LayoutInflater.from(parent.context).inflate(R.layout.posts_data_row, parent, false)
        return ViewHolder(v)
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val usermodel : PostsDataModel = userList[position]
        holder.txt_title.text = "Title :" + usermodel.title
        holder.txt_body.text = "Body :" + usermodel.body
    }

    override fun getItemCount(): Int {
        return userList.size
    }

    class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val txt_title = itemView.txt_title
        val txt_body = itemView.txt_body
    }
}
Step 6:
Create new Package:- retofitdata
DataService.kt
Create new class DataService.kt under retofitdata package and Add following code.
package com.kotlinkatta.retrofitget.retofitdata

import com.kotlinkatta.retrofitget.model.PostsDataModel
import retrofit2.Call
import retrofit2.http.GET

interface DataService {
    @GET("/posts")
    fun getAllPhotos(): Call<List<PostsDataModel>>
}
Step 7:
RetrofitClient.kt
Create new class RetrofitClient.kt under retofitdata package and Add following code.
package com.kotlinkatta.retrofitget.retofitdata

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

object RetrofitClient {
    var retrofit: Retrofit? = null
    var base_url = "https://jsonplaceholder.typicode.com"
    val retrofitInstance: Retrofit
        get() {
            if (retrofit == null) {
                retrofit = Retrofit.Builder()
                    .baseUrl(base_url)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build()
            }
            return retrofit!!
        }
}
Step 8:
MainActivity.kt
Add following code into MainActivity.kt.
package com.kotlinkatta.retrofitget

import android.os.Bundle
import android.view.View
import android.widget.ProgressBar
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.kotlinkatta.retrofitget.adapter.PostsDataAdapter
import com.kotlinkatta.retrofitget.model.PostsDataModel
import com.kotlinkatta.retrofitget.retofitdata.DataService
import com.kotlinkatta.retrofitget.retofitdata.RetrofitClient
import kotlinx.android.synthetic.main.activity_main.*
import retrofit2.Call
import retrofit2.Callback
import retrofit2.Response

class MainActivity : AppCompatActivity() {
    lateinit var recyclerView: RecyclerView
    lateinit var layoutManager:  LinearLayoutManager
    lateinit var progress_bar:  ProgressBar

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        progress_bar = findViewById<ProgressBar>(R.id.progress_bar)
        recyclerView = findViewById<RecyclerView>(R.id.recyclerview)
        layoutManager = LinearLayoutManager(this)
        recyclerview.layoutManager = layoutManager

        fun_getPhotoData()
    }

    private fun fun_getPhotoData() {

        progress_bar.visibility = View.VISIBLE
        
        val service: DataService = RetrofitClient.retrofitInstance!!.create(DataService::class.java)
        val call: Call<List<PostsDataModel>> = service.getAllPhotos()
        call.enqueue(object : Callback<List<PostsDataModel>> {

            override fun onResponse(call: Call<List<PostsDataModel>>,response: Response<List<PostsDataModel>>) {
                val adapter = PostsDataAdapter(response.body()!!)
                recyclerView.adapter = adapter
                progress_bar.visibility = View.GONE
            }

            override fun onFailure(call: Call<List<PostsDataModel>>, t: Throwable) {
                progress_bar.visibility = View.GONE
            }
        })
    }
}
Step 9:
activity_main.xml
Add following code into activity_main.xml.
<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerview"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </androidx.recyclerview.widget.RecyclerView>

    <ProgressBar
        android:id="@+id/progress_bar"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:layout_gravity="center"/>
</androidx.coordinatorlayout.widget.CoordinatorLayout>
OutPut:


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