The preferred approach to data synchronization in Android provides a SyncAdapter for synchronization. You have a very good summary of the necessary steps in this post .
You will also find these articles helpful.
Edit:
1-2-3: You can use a related service to manage the interactions and service methods from your business. You have full working samples in the link provided. Basically, you get attached to the service in your onStart activities and untie onStop .
Remember that the service runs in a user interface thread, so each time-consuming task, such as fetching data over a network, must be performed in a separate thread.
4: you don't need AsyncTask .
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