WatchOS2 WCSession sendMessage doesn't wake iPhone on background

Question

This is being tested on both Simulator and real physical device iphone5s. I tried to use WCSession sendMessage to communicate from WatchOS2 extension to iPhone iOS9 code. It

Answer 1

After hours of trying and hint from @jeron. I finally figured out the problem myself.

In my session:didReceiveMessage delegate method, I have two calls. 1.replyHandler call. 2. I have an async process running (RXPromise) in my case, It nested quite a few RXPromise callbacks to fetch various data from cloud service. I didn't pay attention to it, because it is supposed to call and return right away. But now that I commented out RXPromise block all together, it can wake up iOS app in the background every time.

Finally I figure out the trouble make is because after RXPromise call, it is not guaranty to be landed back to main thread anymore. And I believe session:didReceiveMessage has to be return on the main thread. I didn't see this mentioned anywhere on the Apple documentation.

Final solution:

- (void)session:(WCSession *)session
    didReceiveMessage:(NSDictionary *)message
         replyHandler:(void (^)(NSDictionary *_Nonnull))replyHandler {

    replyHandler(@{ @"schedule" : @"OK" });

    dispatch_async(dispatch_get_main_queue(), ^{
      Nested RXPromise calls.....
    });

}