Java – how do WhatsApp and instant messaging applications run in the background without persistent notifications in Oreo?

What did I learn from stack overflow and Android documentation

Unable to create background service for continuous tasks If I really want a service, I should start a foreground service, and users keep seeing a persistent notification that the application is running This notification cannot be hidden It was intentionally added by Google Yes, there are other options, such as work manager and job scheduler, but they do work periodically and discontinuously

What I want is to build an instant messaging application that uses XMPP or sockets to connect continuously to the server But it requires a continuous connection, but I don't want to use the foreground service because it displays an annoying notice to the user that the application is running

Question 1: how does WhatsApp and other instant messaging applications continuously connect to the server without displaying persistent notifications? How did they do this?

Question 2: if WhatsApp uses FCM for notification, it also applies to those mobile phones that do not have playservices installed. How does the WhatsApp notification mechanism work?

Solution

Starting from Android 6.0 (API level 23), Android has launched two power-saving functions that can extend the user's battery life: doze and app standby When the phone is in nap mode, these two functions impose many restrictions on your background processing You should read about doze and app standby in the following links

https://developer.android.com/training/monitoring-device-state/doze-standby

Now, the use case for you is that you want to receive messages and calls even if the application is not running For this use case, Android released a high priority FCM message in Google IO 2016 They are high priority push messages that grant the application temporary wake-up lock and network access, regardless of the doze state of the device, or the application is just in the application standby state This allows applications to respond to messages and notify users of instant messages or calls in any way

I don't know what WhatsApp does unless I look at their code, but you can use FCM high priority messages to process your use cases For more information about your use case, please follow the link below to visit the Google IO 2016 video between 08:30 and 10:30

And read the use case on the first link of this answer