Retrofit Using Kotlin

Retrofit with Coroutine

In this project, we need a few of the Dependencies for the latest retrofit dependency use https://github.com/square/retrofit. we want a Gson -> Json converter that converts JSON data to Kotlin format Coroutine dependency got from https://github.com/Kotlin/kotlinx.coroutines and Live data and view model add from https://developer.android.com/jetpack/androidx/releases/lifecycle for login intercept implementation(“com.squareup.okhttp3:logginginterceptor:4.11.0”) and kapt dependency and plugin add to build_gradle(Project) file.

plugins {
    id 'com.android.application'
    id 'org.jetbrains.kotlin.android'
    id 'kotlin-kapt'  //for Annotation processor
}

android {
    namespace 'com.posibolt.retrofitdemo'
    compileSdk 33

    defaultConfig {
        applicationId "com.posibolt.retrofitdemo"
        minSdk 24
        targetSdk 33
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }
}

dependencies {
    implementation 'androidx.core:core-ktx:1.7.0'
    implementation 'androidx.appcompat:appcompat:1.6.1'
    implementation 'com.google.android.material:material:1.9.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.4'
    //Retrofit https://square.github.io/retrofit/ - latest vesion https://github.com/square/retrofit.
    implementation 'com.squareup.retrofit2:retrofit:2.9.0'
    //Gson -> json data to java or kotlin format
    implementation 'com.squareup.retrofit2:converter-gson:2.9.0'
    //coroutines -> https://github.com/Kotlin/kotlinx.coroutines
    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.7.2")
    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.7.2")
    //Viewmodel and livedata -> https://developer.android.com/jetpack/androidx/releases/lifecycle
    // ViewModel
    implementation("androidx.lifecycle:lifecycle-viewmodel-ktx:2.6.1")
    // LiveData
    implementation("androidx.lifecycle:lifecycle-livedata-ktx:2.6.1")
    // Annotation processor
    kapt("androidx.lifecycle:lifecycle-compiler:2.6.1")
    // login intercept
    implementation("com.squareup.okhttp3:logging-interceptor:4.11.0")
    //jsonplaceholder.typecode.com -> test api
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.5'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'
}

2. Test purpose API data we got from jsonplaceholder.typecode.com.

3. Create a Data class based on JSON

AlbumItem.kt :

package com.posibolt.retrofitdemo
import com.google.gson.annotations.SerializedName

data class AlbumItem(
    @SerializedName("id")
    val id: Int,
    @SerializedName("title")
    val title: String,
    @SerializedName("userId")
    val userId: Int
)

Album.kt :

package com.posibolt.retrofitdemo

class Album : ArrayList<AlbumItem>()

4. Mainly Retrofit contains a retrofitInstance class and a service class

RetrofitInstance.kt :

package com.posibolt.retrofitdemo
import com.google.gson.GsonBuilder
import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory

class RetrofitInstance {

    companion object{
        val BASE_URL = "https://jsonplaceholder.typicode.com"

        fun getRetrofitInstance():Retrofit{
            return Retrofit.Builder().baseUrl(BASE_URL)
                .addConverterFactory(GsonConverterFactory.create(GsonBuilder().create())).build()
        }
    }
}

Specify your Base URL here..!

AlbumService.kt :

package com.posibolt.retrofitdemo
import retrofit2.Response
import retrofit2.http.GET
import retrofit2.http.Query

interface AlbumService {

    @GET("/albums")
    suspend fun getAlbums(): Response<Album>

}

Here we can specify our method and parameter with the help of a return type function.

5. activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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">

    <ScrollView
        android:id="@+id/scrollView2"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginStart="1dp"
        android:layout_marginTop="1dp"
        android:layout_marginEnd="1dp"
        android:layout_marginBottom="1dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <TextView
            android:id="@+id/textView"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:textSize="20dp"
            android:layout_marginBottom="356dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/scrollView2" />

    </ScrollView>

</androidx.constraintlayout.widget.ConstraintLayout>

Textview inside scroll view -> just API data viewing like abow

6. MainActivity.kt

package com.posibolt.retrofitdemo
import android.annotation.SuppressLint
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.widget.TextView
import androidx.lifecycle.LiveData
import androidx.lifecycle.Observer
import androidx.lifecycle.liveData
import retrofit2.Response

class MainActivity : AppCompatActivity() {
    @SuppressLint("MissingInflatedId")
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val text_view : TextView = findViewById(R.id.textView)
        val retService : AlbumService = RetrofitInstance.getRetrofitInstance().create(AlbumService::class.java)
        val responceLiveData : LiveData<Response<Album>> = liveData {
            val  response: Response<Album> = retService.getAlbums()
            emit(response)
        }
        responceLiveData.observe(this, Observer {
            val  albumList : MutableListIterator<AlbumItem>? = it.body()?.listIterator()
            if(albumList != null){
                while (albumList.hasNext()){
                    val albumItem : AlbumItem = albumList.next()
                    Log.i("MYTAG",albumItem.title)
                    val result: String = " "+"Album id : ${albumItem.id}"+"\n"+
                            " "+"Album title : ${albumItem.title}"+"\n"+
                            " "+"Album userid : ${albumItem.userId}"+"\n"+"\n"
                    text_view.append(result)
                }
            }
        })
    }
}