Check `[[UIApplication sharedApplication] applicationState]` from background thread, without throwing warning in Xcode 9?

Question

I need to check if the app is in the background and what its backgroundTimeRemaining is, from a non-main-thread. — Apparently this is no longer allowed without throwing the warning. I filed a radar but Apple said this works as intended.

So, if you're not on the main thread, how do you check these properties? Cache them to other variables that don't throw this warning? Seems silly...

Answer 1

The solution is, indeed, checking backgroundTimeRemaining in a dispatch_get_main_queue block or storing the value in a temporary variable.

dispatch_async(dispatch_get_main_queue(), ^{
  double bgTime = [UIApplication sharedApplication].backgroundTimeRemaining;
});