问题
ContentProvided defined for synchronization is dummy (in accordance with this approach).
回答1:
If API > 8, (95% of devices) use ContentResolver.addPeriodicSync()
If API = 7, (5.5% of devices as of Mar 2102) create a service with a periodic timer callback, and call ContentResolver.requestSync().
API < 6 does not support syncAdapter, so no worries.
来源：https://stackoverflow.com/questions/5525593/how-to-define-frequency-of-syncadapter-updates-on-android