How to make Notification appear on the phone for Android Studio?

Question

I want to create a push notification where Admin can send notification to all users. I found a tutorial and follow it but it doesn't work. I'm not sure where I did wrong but I got error that said

Developer Warning for package "... " Failed to post notification on channel "null"

 b1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String tittle = ed1.getText().toString().trim();
                String subject = ed2.getText().toString().trim();
                String body = ed3.getText().toString().trim();

                NotificationManager notif = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
                Notification notify = new Notification.Builder
                        (getApplicationContext()).setContentTitle(tittle).setContentText(body).
                        setContentTitle(subject).setSmallIcon(R.drawable.ps).build();

                notify.flags |= Notification.FLAG_AUTO_CANCEL;
                notif.notify(0, notify);
            }
        });

Answer 1

If you want to send multiple notifications at same instance .

 // Create the NotificationChannel, but only on API 26+ because
    // the NotificationChannel class is not in the Support Library.
    val mBuilder = NotificationCompat.Builder(LocalContext.current,     "channel_id")
    mBuilder.setSmallIcon(android.R.drawable.stat_notify_chat);
    mBuilder.setPriority(NotificationCompat.PRIORITY_MAX);
    mBuilder.setGroup("dicer app group")

for (item in itemList) {
    
    mBuilder.setContentTitle(item.name);
    mBuilder.setContentText(item.details);
   
   
     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            val name = ("channel_name")
            val descriptionText = "channel_description"
            val importance = NotificationManager.IMPORTANCE_DEFAULT
            val channel = NotificationChannel("channel_id", name, importance).apply {
                description = descriptionText
            }

           val notificationManager = getSystemService(LocalContext.current, NotificationManager::class.java) as NotificationManager
        
           notificationManager.createNotificationChannel(channel)
           notificationManager.notify(item.id, mBuilder.build())

        }
 

Answer 2

     public void sendNotification (String message, String title ){

        Intent intent = new Intent(getApplicationContext(), CampaignActivity.class);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0 , intent,
                PendingIntent.FLAG_IMMUTABLE);


        String channelId = "some_channel_id";
        Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
        NotificationCompat.Builder notificationBuilder =
                new NotificationCompat.Builder(this, channelId)
                        .setSmallIcon(R.mipmap.ic_launcher_round)
//                        .setContentTitle(getString(R.string.app_name)
                        .setContentTitle(title)
                        .setContentText(message)
                        .setAutoCancel(true)
                        .setSound(defaultSoundUri)
                        .setContentIntent(pendingIntent);

        NotificationManager notificationManager =
                (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

        // Since android Oreo notification channel is needed.
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel channel = new NotificationChannel(channelId,
                    "Channel human readable title",
                    NotificationManager.IMPORTANCE_DEFAULT);
            assert notificationManager != null;
            notificationManager.createNotificationChannel(channel);
        }

        assert notificationManager != null;
        notificationManager.notify(0 /* ID of notification */, notificationBuilder.build());
    }

Answer 3

After Oreo SDK you have to create Notification channel in order to show a notification, check this method for reference:

/**
 *
 * @param context
 * @param title  --> title to show
 * @param message --> details to show
 * @param intent --> What should happen on clicking the notification
 * @param reqCode --> unique code for the notification
 */

public void showNotification(Context context, String title, String message, Intent intent, int reqCode) {
    SharedPreferenceManager sharedPreferenceManager = SharedPreferenceManager.getInstance(context);

    PendingIntent pendingIntent = PendingIntent.getActivity(context, reqCode, intent, PendingIntent.FLAG_ONE_SHOT);
    String CHANNEL_ID = "channel_name";// The id of the channel.
    NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(context, CHANNEL_ID)
            .setSmallIcon(R.mipmap.notification_logo)
            .setContentTitle(title)
            .setContentText(message)
            .setAutoCancel(true)
            .setSound(RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION))
            .setContentIntent(pendingIntent);
    NotificationManager notificationManager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        CharSequence name = "Channel Name";// The user-visible name of the channel.
        int importance = NotificationManager.IMPORTANCE_HIGH;
        NotificationChannel mChannel = new NotificationChannel(CHANNEL_ID, name, importance);
        notificationManager.createNotificationChannel(mChannel);
    }
    notificationManager.notify(reqCode, notificationBuilder.build()); // 0 is the request code, it should be unique id

    Log.d("showNotification", "showNotification: " + reqCode);
}

How to use this method:

    int reqCode = 1;
    Intent intent = new Intent(getApplicationContext(), MainActivity.class);
    showNotification(this, "Title", "This is the message to display", intent, reqCode);