How to group android notifications like whatsapp?

Question

I don´t know how to group two or more notifications into only one and show a message like \"You have two new messages\".

Answer 1

You need to create the notification so that it can be updated with a notification ID by calling NotificationManager.notify(ID, notification).

The following steps need to be created to update the notification:

1. Update or create a NotificationCompat.Builder object
2. Build a Notification object from it
3. Issue the Notification with the same ID you used previously

An example taken from the android developer docs:

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

// Sets an ID for the notification, so it can be updated
int notifyID = 1;

mNotifyBuilder = new NotificationCompat.Builder(this)
    .setContentTitle("New Message")
    .setContentText("You've received new messages.")
    .setSmallIcon(R.drawable.ic_notify_status)
numMessages = 0;

// Start of a loop that processes data and then notifies the user
...
mNotifyBuilder.setContentText(currentText).setNumber(++numMessages);

// Because the ID remains unchanged, the existing notification is updated.
mNotificationManager.notify(notifyID, mNotifyBuilder.build());
...

Also see the Android docs on Stacking Notifications https://developer.android.com/training/wearables/notifications/stacks.html