How to keep my android app run on background.

I am build a app with Xamarin.Forms.
My app have two target platforms, android and UWP.
My app is a chat client, and I create a work thread to receive network data.
In my android version, when the app go background it only have minutes to run , then the work thread will be suspend.

I need to find a way to make sure my work thread not be suspend.
I think this function only can be write to android code and can't write to PCL code.
Am I right?

My android project's setting:
Minimum Android version: Android 4.4 (API Level 19 - Kit Kat)
Target Android version: Android 8.1 (API Level 27 - Oreo)