Show Notification in Android

 A notification is a message that appears outside an application's UI to get user attention, provide reminders, notify about events, etc. A typical notification consists of a small icon, title, and content text.

Android 8.0 (API level 26) and higher versions of the platform, requires that notification should be assigned to a channel, otherwise it will not appear. A channel allows grouping notifications. User can manage settings of specific notification channel instead of managing all notifications individually.

First we need to construct a NotificationChannel object with a unique channel ID, a name, and an importance level. After that, a notification channel should be created using the method createNotificationChannel(). This method can be called multiple times with the same channel ID used previously, the channel will not be created again.

A notification can be build using Notification.Builder. The method notify() can be used to display a notification. This method requires the notification ID. It can be used later if you want to update or remove the notification.

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package com.example.camera3;

import android.app.Notification;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Intent;
import android.os.Bundle;

import androidx.appcompat.app.AppCompatActivity;

public class notification extends AppCompatActivity {

    private String channelId = "my_channel";
    private NotificationManager notifManager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_notification);

      showNotification(1);
       showNotification(2);
      
    }

    private void showNotification(int id) {
    String channelId = "my_channel";
    final int NOTIFY_ME_ID=id;
    /*********** Create notification channel ***********/
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        NotificationChannel channel = new NotificationChannel(channelId, "MyChannel", NotificationManager.IMPORTANCE_DEFAULT);
        NotificationManager notificationManager = getSystemService(NotificationManager.class);
        notificationManager.createNotificationChannel(channel);
    }
    /*********** Create notification ***********/
    NotificationCompat.Builder builder = new NotificationCompat.Builder(this, channelId)
            .setSmallIcon(R.drawable.ic_launcher_foreground)
            .setContentTitle("Android Example Notification Title")
            .setContentText("This is the android example notification message")
            .setPriority(NotificationCompat.PRIORITY_HIGH)
            .setAutoCancel(true);

    // This pending intent will open after notification click
    Intent intent = new Intent(this,StudentNotificationActivity.class);
    PendingIntent i = PendingIntent.getActivity(this, 0, new Intent(this, StudentNotificationActivity.class), PendingIntent.FLAG_IMMUTABLE);

    builder.setContentIntent(i);

    NotificationManagerCompat notificationManagerCompat = NotificationManagerCompat.from(this);
    notificationManagerCompat.notify(NOTIFY_ME_ID, builder.build());
    }
    private void showMultipleNotifications(ArrayList<StudentNotification> notificationArrayList) {
            // one notification in multiple show        
         int notificationId = 1;
        final int NOTIFY_ME_ID = 1337;

        /*********** Create notification channel ***********/
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel channel = new NotificationChannel(channelId, "MyChannel", NotificationManager.IMPORTANCE_DEFAULT);
            NotificationManager notificationManager = getSystemService(NotificationManager.class);
            notificationManager.createNotificationChannel(channel);
        }

        Bitmap bitmap = null;
        /*********** Create notifications ***********/
        for (StudentNotification student : notificationArrayList) {
            String imageURL = Api.BASE_URL + "api/get-user-image/UserImages/" + "Student" + "/" + student.getImage();
//      
           NotificationCompat.Builder builder = new NotificationCompat.Builder(this, channelId)
                    .setSmallIcon(R.drawable.ic_launcher_foreground)
                    .setContentTitle(student.getCourseName())
                    .setContentText(student.getName() + "\n" + student.getDate())
                    .setPriority(NotificationCompat.PRIORITY_HIGH)
                    .setAutoCancel(true);

            // This pending intent will open after notification click
            Intent intent = new Intent(this, StudentNotificationActivity.class);
            PendingIntent i = PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_IMMUTABLE);
            builder.setContentIntent(i);

            NotificationManagerCompat notificationManagerCompat = NotificationManagerCompat.from(this);
            notificationManagerCompat.notify(notificationId++, builder.build());
        }
    }
}