How to use Radio Button in Android Kotlin?

This example demonstrates how to use Radio Button in Android 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:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context=".MainActivity">
   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerHorizontal="true"
      android:layout_marginTop="50dp"
      android:text="Tutorials Point"
      android:textAlignment="center"
      android:textColor="@android:color/holo_green_dark"
      android:textSize="32sp"
      android:textStyle="bold" />
   <TextView
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_above="@id/radioGroup"
      android:text="Who is the best player in the world?"
      android:textAlignment="center"
      android:textColor="@android:color/background_dark"
      android:textSize="24sp"
      android:textStyle="bold|italic" />
   <RadioGroup
      android:id="@+id/radioGroup"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerInParent="true">
   <RadioButton
      android:id="@+id/radioBtn1"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:checked="true"
      android:text="Lionel Messi" />
   <RadioButton
      android:id="@+id/radioBtn2"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Cristiano Ronaldo" />
   </RadioGroup>
   <Button
      android:id="@+id/btnDisplay"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_below="@id/radioGroup"
      android:layout_centerInParent="true"
      android:text="Display" />
</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.Toast
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
   var radioGroup: RadioGroup? = null
   lateinit var radioButton: RadioButton
   private lateinit var button: Button
   override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      title = "KotlinApp"
      radioGroup = findViewById(R.id.radioGroup)
      button = findViewById(R.id.btnDisplay)
      button.setOnClickListener {
         val intSelectButton: Int = radioGroup!!.checkedRadioButtonId
         radioButton = findViewById(intSelectButton)
         Toast.makeText(baseContext, radioButton.text, Toast.LENGTH_SHORT).show()
      }
   }
}
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.kotlipapp">
   <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 the 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 −
Click here to download the project code.