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

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);