AlarmManager + NoficationManager

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    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="match_parent"
        android:layout_height="wrap_content"
        android:text="Button" />

</LinearLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.elevintech.alarmmanager">

    <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>

        <receiver android:name=".MainActivity$Receiver"/>
    </application>

</manifest>

MainActivity.kt

package com.elevintech.alarmmanager

import android.app.*
import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.graphics.Color
import android.os.Build
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.core.app.NotificationCompat
import androidx.core.app.NotificationManagerCompat
import androidx.core.content.ContextCompat.getSystemService
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

    lateinit var alarmManager: AlarmManager




    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        alarmManager = getSystemService(Context.ALARM_SERVICE) as AlarmManager


        button.setOnClickListener {



            val intent = Intent(this, Receiver::class.java)
            val pendingIntent = PendingIntent.getBroadcast(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT)
            println("button is clicked")
            alarmManager.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + 4000, pendingIntent)


        }
    }

    class Receiver: BroadcastReceiver(){
//        lateinit var notificationManager: NotificationManagerCompat
//        lateinit var notificationChannel: NotificationChannel
//        lateinit var builder: Notification.Builder
        var channelId = "com.elevintech.alarmmanager"
        var description = "Notify Odometer"

        override fun onReceive(p0: Context?, p1: Intent?) {
//
//            val builder = NotificationCompat.Builder(p0!!, channelId)
//                .setSmallIcon(R.drawable.ic_launcher_background)
//                .setContentTitle("This is my title")
//                .setContentText("This is my text")
//                .setPriority(NotificationManagerCompat.IMPORTANCE_HIGH)
//
//            val notificationManager = NotificationManagerCompat.from(p0)
//
//            notificationManager.notify(200, builder
//                .build())
//            println("message received")
////
////            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
////                notificationChannel = NotificationChannel(channelId, description, NotificationManager.IMPORTANCE_HIGH )
////                notificationChannel.enableLights(true)
////                notificationChannel.lightColor = Color.BLUE
////                notificationChannel.enableVibration(false)
////                notificationManager.createNotificationChannel(notificationChannel )
////            }

            var builder = NotificationCompat.Builder(p0!!, channelId)
                .setSmallIcon(R.drawable.ic_launcher_background)
                .setContentTitle("some titlez")
                .setContentText("some text")
                .setDefaults(Notification.DEFAULT_VIBRATE) //Important for heads-up notification
                .setPriority(Notification.PRIORITY_MAX) //Important for heads-up notification


            val manager = p0!!.getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
            manager.notify(0, builder.build())


        }


    }
}