How to get the selected index of a RadioGroup in Android using Kotlin?

This example demonstrates how to get the selected index of a RadioGroup in Android using Kotlin.
Step 1 − Create a new project in Android Studio, go to File ? New Project and fill all
required details to create a new project.
Step 2 − Add the following code to res/layout/activity_main.xml.
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
   android:id="@+id/rl"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:padding="10dp"
   tools:context=".MainActivity">
   <TextView
      android:layout_marginTop="30dp"
      android:id="@+id/textView"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Which is your most favorite?"
      android:textSize="16sp"
      android:textStyle="bold" />
   <RadioGroup
      android:id="@+id/radioGroup"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_below="@id/textView"
      android:orientation="vertical"
      android:padding="15dp"
      android:paddingTop="30dp">
   <RadioButton
      android:id="@+id/rbNetflix"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:paddingEnd="15dp"
      android:text="Netflix" />
   <RadioButton
      android:id="@+id/rbAmazonPrime"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:paddingEnd="15dp"
      android:text="Amazon Prime" />
   </RadioGroup>
   <Button
      android:id="@+id/btnGetItem"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_below="@+id/radioGroup"
      android:text="Get Selected Radio Button" />
   <TextView
      android:id="@+id/tvResult"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_below="@id/btnGetItem"
      android:paddingBottom="15dp" />
</RelativeLayout>
Step 3 − Add the following code to src/MainActivity.kt
import android.os.Bundle
import android.widget.Button
import android.widget.RadioButton
import android.widget.RadioGroup
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
   private lateinit var textView: TextView
   private lateinit var button: Button
   private lateinit var radioGroup: RadioGroup
   private lateinit var selectedRadioButton: RadioButton
   override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      title = "KotlinApp"
      textView = findViewById(R.id.textView)
      button = findViewById(R.id.btnGetItem)
      radioGroup = findViewById(R.id.radioGroup)
      button.setOnClickListener {
         val selectedRadioButtonId: Int = radioGroup.checkedRadioButtonId
         if (selectedRadioButtonId != -1) {
            selectedRadioButton = findViewById(selectedRadioButtonId)
            val string: String = selectedRadioButton.text.toString()
            textView.text = "$string is Selected"
         } else {
            textView.text = "Nothing selected from the radio group"
         }
      }
   }
}
Step 4 − Add the following code to androidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="app.com.q15">
   <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=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>
Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click the Run icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen