How to create a notification alert using Kotlin?

This example demonstrates how to create a notification alert 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: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">
   <Button
      android:id="@+id/textView"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerInParent="true"
      android:onClick="btnNotify"
      android:text="Show Notification" />
</RelativeLayout>
Step 3 − Add the following code to src/MainActivity.kt
package app.com.kotlinapp
import android.app.*
import android.content.Context
import android.content.Intent
import android.graphics.BitmapFactory
import android.graphics.Color
import android.os.Build
import android.os.Bundle
import android.view.View
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
   lateinit var notificationChannel: NotificationChannel
   lateinit var notificationManager: NotificationManager
   lateinit var builder: Notification.Builder
   private val channelId = "12345"
   private val description = "Test Notification"
   override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as
      NotificationManager
   }
   fun btnNotify(view: View) {
      val intent = Intent(this, LauncherActivity::class.java)
      val pendingIntent = PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT)
      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
         notificationChannel = NotificationChannel(channelId, description, NotificationManager .IMPORTANCE_HIGH)
         notificationChannel.lightColor = Color.BLUE notificationChannel.enableVibration(true)
         notificationManager.createNotificationChannel(notificationChannel)
         builder = Notification.Builder(this, channelId).setContentTitle("NOTIFICATION USING " +
"KOTLIN").setContentText("Test Notification").setSmallIcon(R.drawable .ic_brightness).setLargeIcon(BitmapFactory.decodeResource(this.resources, R.drawable
.ic_launcher_background)).setContentIntent(pendingIntent)
      }
      notificationManager.notify(12345, builder.build())
   }
}
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.kotlinapp">
   <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 −
Click here to download the project code.