【ANDROID STUDIO】Notifications Kotlin

package com.example.notificationdemo

import android.app.NotificationChannel
import android.app.NotificationManager
import android.content.Context
import android.os.Build
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.core.app.NotificationCompat
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {
    private val channelID = "com.example.notificationdemo.channel1"
    private var notificationManager: NotificationManager? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
        createNotificationChannel(channelID,"DemoChannel","this is a demo")
        button.setOnClickListener {
            displayNotification()


        }
    }
    private fun displayNotification() {
        val notificationId = 45
        val notification = NotificationCompat.Builder(this@MainActivity, channelID)
            .setContentTitle("Demo Title")
            .setContentText("This is a demo notification")
            .setSmallIcon(android.R.drawable.ic_dialog_info)
            .setAutoCancel(true)
            .setPriority(NotificationCompat.PRIORITY_DEFAULT)
            .build()
        notificationManager?.notify(notificationId, notification)

    }

    private fun createNotificationChannel(id : String, name:String, channelDescription:String) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            val importance = NotificationManager.IMPORTANCE_HIGH
            val channel = NotificationChannel(id, name, importance).apply {
                description = channelDescription
            }
            notificationManager?.createNotificationChannel(channel)

        }

    }

}

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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=".MainActivity">

    <Button android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />


</androidx.constraintlayout.widget.ConstraintLayout>