Notifications in Kotlin Oreo (8+)

Create a new Project in Kotlin

Message can display outside of our application normal UI

1 Open Android Studio.
2 Go to File => New => New Project. Write application name . Then, check Include Kotlin Support and click next button.
3Select minimum SDK you need. However, we have selected 17 as minimum SDK. Then, click next button
4 Then, select Empty Activity => click next => click finish.
5 You will get a newly created project successfully if you have followed steps properly.

added line in the build.gradle (Module: app) dependencies:

implementation 'com.android.support:appcompat-v7:26.1.0'

Use the below code to Implement a Notification with Kotlin

 MainActivity.k

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.*
import kotlinx.android.synthetic.main.activity_main.*
import android.widget.RadioGroup
import android.widget.Toast
import android.app.NotificationManager
import android.support.v4.app.NotificationCompat
import android.os.Build
import android.app.NotificationChannel
import android.content.Context
import android.support.annotation.RequiresApi
class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
   val button:Button=findViewById(R.id.button);
        button.setOnClickListener()

        {

            issueNotification()

        }
    }


    @RequiresApi(api = Build.VERSION_CODES.O)
    fun makeNotificationChannel(id: String, name: String, importance: Int) {
        val channel = NotificationChannel(id, name, importance)
        channel.setShowBadge(true) // set false to disable badges, Oreo exclusive

        val notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager

        notificationManager.createNotificationChannel(channel)
    }


    fun issueNotification() {

        // make the channel. The method has been discussed before.
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            makeNotificationChannel("CHANNEL_1", "Example channel", NotificationManager.IMPORTANCE_DEFAULT)
        }
        // the check ensures that the channel will only be made
        // if the device is running Android 8+

        val notification = NotificationCompat.Builder(this, "CHANNEL_1")
        // the second parameter is the channel id.
        // it should be the same as passed to the makeNotificationChannel() method

        notification
            .setSmallIcon(R.mipmap.ic_launcher) // can use any other icon
            .setContentTitle("Notification!")
            .setContentText("This is an Oreo notification!")
            .setNumber(3) // this shows a number in the notification dots

        val notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager

        notificationManager.notify(1, notification.build())
        // it is better to not use 0 as notification id, so used 1.
    }


}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/root_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
 <Button

            android:id="@+id/button"
            android:layout_gravity="center"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="15dp"
            android:text="click"
    />
</LinearLayout>