CreateNotification.kt

package com.example.myapplication

import android.app.NotificationChannel
import android.app.NotificationManager
import android.app.PendingIntent.FLAG_IMMUTABLE
import android.content.Context
import android.os.Build
import androidx.core.app.NotificationCompat
import androidx.core.app.TaskStackBuilder

const val NOTIFICATION_CHANNEL_ID = BuildConfig.APPLICATION_ID + ".channel"

/**
 * @author Nav Singh
 */
fun sendNotification(context: Context) {
    val notificationManager = context
        .getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
    // We need to create a NotificationChannel associated with our CHANNEL_ID before sending a notification.
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O &&
        notificationManager.getNotificationChannel(NOTIFICATION_CHANNEL_ID) == null
    ) {
        val name = context.getString(R.string.app_name)
        val channel = NotificationChannel(
            NOTIFICATION_CHANNEL_ID,
            name,
            NotificationManager.IMPORTANCE_DEFAULT
        )
        notificationManager.createNotificationChannel(channel)
    }

    val intent = MainActivity.newIntent(context.applicationContext)

    // create a pending intent that opens MainActivity when the user clicks on the notification
    val stackBuilder = TaskStackBuilder.create(context)
        .addParentStack(MainActivity::class.java)
        .addNextIntent(intent)
    val notificationPendingIntent = stackBuilder
        .getPendingIntent(getUniqueId(), FLAG_IMMUTABLE)

//    build the notification object with the data to be shown
    val notification = NotificationCompat.Builder(context, NOTIFICATION_CHANNEL_ID)
        .setSmallIcon(R.mipmap.ic_launcher)
        .setContentTitle("Title")
        .setContentText("Content goes here")
        .setContentIntent(notificationPendingIntent)
        .setAutoCancel(true)
        .build()

    notificationManager.notify(getUniqueId(), notification)
}

private fun getUniqueId() = ((System.currentTimeMillis() % 10000).toInt())