About a year we made a tutorial on using RxJava and Retrofit in Android.
Today we are going to make a similar tutorial in Kotlin. We will be parsing JSON data from URL and display it in a RecyclerView using Retrofit and RxJava. We parse the JSON array from the URL.
Here I have created an Android Studio project with package com.learn2crack.retrofitkotlin also Activity as MainActivity and layout as activity_main. Don’t forget to check Include Kotlin support option while creating a new project.
The dependencies we require are,
implementation 'com.android.support:recyclerview-v7:26.1.0'
implementation 'com.android.support:cardview-v7:26.1.0'
implementation 'com.android.support.constraint:constraint-layout:1.0.2'
implementation 'com.squareup.retrofit2:retrofit:2.3.0'
implementation 'com.squareup.retrofit2:converter-gson:2.3.0'
implementation 'com.squareup.retrofit2:adapter-rxjava2:2.3.0'
implementation 'io.reactivex.rxjava2:rxjava:2.1.6'
implementation 'io.reactivex.rxjava2:rxandroid:2.0.1'We have added the dependencies for RxJava, Retrofit, Card View, Recycler View and ConstraintLayout.
apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
android {
compileSdkVersion 26
defaultConfig {
applicationId "com.learn2crack.retrofitkotlin"
minSdkVersion 21
targetSdkVersion 26
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation"org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
implementation 'com.android.support:appcompat-v7:26.1.0'
implementation 'com.android.support:recyclerview-v7:26.1.0'
implementation 'com.android.support:cardview-v7:26.1.0'
implementation 'com.android.support.constraint:constraint-layout:1.0.2'
implementation 'com.squareup.retrofit2:retrofit:2.3.0'
implementation 'com.squareup.retrofit2:converter-gson:2.3.0'
implementation 'com.squareup.retrofit2:adapter-rxjava2:2.3.0'
implementation 'io.reactivex.rxjava2:rxjava:2.1.6'
implementation 'io.reactivex.rxjava2:rxandroid:2.0.1'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.1'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
}We need permission to access the Internet.
<uses-permission android:name="android.permission.INTERNET"/>Our main layout has only one RecyclerView widget.
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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="com.learn2crack.retrofitkotlin.MainActivity">
<android.support.v7.widget.RecyclerView
android:id="@+id/rv_android_list"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>The next layout is for RecylerView list item. It has three TextView widgets to display Android version name, version number, and API level.
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="1dp"
android:foreground="?android:attr/selectableItemBackground">
<TextView
android:id="@+id/tv_name"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:textColor="@android:color/white"
android:textSize="24sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@+id/tv_version"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:textColor="@android:color/white"
android:textSize="18sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/tv_name" />
<TextView
android:id="@+id/tv_api_level"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:textColor="@android:color/white"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/tv_version" />
</android.support.constraint.ConstraintLayout>We create Kotlin data class to store Android version name, version number, and API level.
package com.learn2crack.retrofitkotlin.model
data class Android(val name : String, val version : String, val apiLevel : String)A single line of definition is enough. We need to add data before the class definition. That’s all, It takes care of everything required. This Android class is created in the model package.
The getData() method is defined to fetch data and an Observable is returned. The endpoint is defined as “api/android” with GET HTTP method. This Retrofit Interface is created in the network package.
package com.learn2crack.retrofitkotlin.network
import com.learn2crack.retrofitkotlin.model.Android
import io.reactivex.Observable
import retrofit2.http.GET
interface RequestInterface {
@GET("api/android")
fun getData() : Observable<List<Android>>
}We pass the data as an ArrayList in constructor along with a Listener which we use to track RecyclerView item clicks. We also defined an array of hexadecimal colors which we set as a background in RecyclerView Item. We have created a ViewHolder class which takes care of binding of data in RecyclerView Item Views. Setting text to TextView is as simple as,
itemView.tv_name.text = android.name
where tv_name is the Id of the TextView and it is set using text property. This Adapter kotlin class is created in the adapter package.
package com.learn2crack.retrofitkotlin.adapter
import android.support.v7.widget.RecyclerView
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.graphics.Color
import com.learn2crack.retrofitkotlin.R
import com.learn2crack.retrofitkotlin.model.Android
import kotlinx.android.synthetic.main.recycler_view_row.view.*
class DataAdapter (private val dataList : ArrayList<Android>, private val listener : Listener) : RecyclerView.Adapter<DataAdapter.ViewHolder>() {
interface Listener {
fun onItemClick(android : Android)
}
private val colors : Array<String> = arrayOf("#EF5350", "#EC407A", "#AB47BC", "#7E57C2", "#5C6BC0", "#42A5F5")
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
holder.bind(dataList[position], listener, colors, position)
}
override fun getItemCount(): Int = dataList.count()
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val view = LayoutInflater.from(parent.context).inflate(R.layout.recycler_view_row, parent, false)
return ViewHolder(view)
}
class ViewHolder(view : View) : RecyclerView.ViewHolder(view) {
fun bind(android: Android, listener: Listener, colors : Array<String>, position: Int) {
itemView.tv_name.text = android.name
itemView.tv_version.text = android.version
itemView.tv_api_level.text = android.apiLevel
itemView.setBackgroundColor(Color.parseColor(colors[position % 6]))
itemView.setOnClickListener{ listener.onItemClick(android) }
}
}
}We initialize a CompositeDisposable object and add all the RxJava disposable to it. During onDestroy() we can clear the disposables so that it prevents the memory leak.
The RecyclerView is initialised using initRecyclerView() method. The Retrofit request is defined using
val requestInterface = Retrofit.Builder()
.baseUrl(BASE_URL)
.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
.addConverterFactory(GsonConverterFactory.create())
.build().create(RequestInterface::class.java)To use RxJava Observable along with Retrofit, we need to use a new Adapter Factory implementation. It is done by using addCallAdapterFactory() method.
The network operation is carried out by,
requestInterface.getData()
.observeOn(AndroidSchedulers.mainThread())
.subscribeOn(Schedulers.io())
.subscribe(this::handleResponse, this::handleError)The above code returns a Disposable. The observeOn() and subscribeOn() defines, in which thread we need to handle the results and perform the network operation. Here we have defined the results should be delivered and handled in the main thread and the network operation should be handled in IO thread. The handleResponse() and handleError() methods are called for success and failure. A Toast is displayed when an item is clicked in the RecyclerView.
package com.learn2crack.retrofitkotlin
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.support.v7.widget.LinearLayoutManager
import android.support.v7.widget.RecyclerView
import android.util.Log
import android.widget.Toast
import io.reactivex.disposables.CompositeDisposable
import io.reactivex.schedulers.Schedulers
import io.reactivex.android.schedulers.AndroidSchedulers
import retrofit2.converter.gson.GsonConverterFactory
import retrofit2.adapter.rxjava2.RxJava2CallAdapterFactory
import retrofit2.Retrofit
import com.learn2crack.retrofitkotlin.network.RequestInterface
import com.learn2crack.retrofitkotlin.adapter.DataAdapter
import com.learn2crack.retrofitkotlin.model.Android
import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity(), DataAdapter.Listener {
private val TAG = MainActivity::class.java.simpleName
private val BASE_URL = "https://learn2crack-json.herokuapp.com"
private var mCompositeDisposable: CompositeDisposable? = null
private var mAndroidArrayList: ArrayList<Android>? = null
private var mAdapter: DataAdapter? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
mCompositeDisposable = CompositeDisposable()
initRecyclerView()
loadJSON()
}
private fun initRecyclerView() {
rv_android_list.setHasFixedSize(true)
val layoutManager : RecyclerView.LayoutManager = LinearLayoutManager(this)
rv_android_list.layoutManager = layoutManager
}
private fun loadJSON() {
val requestInterface = Retrofit.Builder()
.baseUrl(BASE_URL)
.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
.addConverterFactory(GsonConverterFactory.create())
.build().create(RequestInterface::class.java)
mCompositeDisposable?.add(requestInterface.getData()
.observeOn(AndroidSchedulers.mainThread())
.subscribeOn(Schedulers.io())
.subscribe(this::handleResponse, this::handleError))
}
private fun handleResponse(androidList: List<Android>) {
mAndroidArrayList = ArrayList(androidList)
mAdapter = DataAdapter(mAndroidArrayList!!, this)
rv_android_list.adapter = mAdapter
}
private fun handleError(error: Throwable) {
Log.d(TAG, error.localizedMessage)
Toast.makeText(this, "Error ${error.localizedMessage}", Toast.LENGTH_SHORT).show()
}
override fun onItemClick(android: Android) {
Toast.makeText(this, "${android.name} Clicked !", Toast.LENGTH_SHORT).show()
}
override fun onDestroy() {
super.onDestroy()
mCompositeDisposable?.clear()
}
}
