Cyclically test a variable

Question

I'm developing an app and I need to verify if a given variable has the same value for a given time. How can I do it? Maybe a solution can be to use a thread and manually force this to test my variable each 100 millisecond (with the equivalent of the C function "wait" or something like that). Is it correct? I think (and hope) there's a more elegant solution.

Specifically, I'm working with beacons and I need to trigger a method when a beacon is immediate to my device for an amount of time.

Answer 1

When ranging CLBeacons, you get a callback from the operating system every second anyway, so it may be easier to simply put your logic inside this callback method. Like this:

  NSMutableDictionary *immediateRangeBeaconTimes;
  ...

  - (void)locationManager:(CLLocationManager *)manager didRangeBeacons:(NSArray *)iBeacons inRegion:(CLBeaconRegion *)region {
      NSDate *now = [NSDate new];
      for (CLBeacon *iBeacon in iBeacons) {
          NSString *key = [NSString stringWithFormat:@"%@ %@ %@", iBeacon.proximityUUID, iBeacon.major, iBeacon.minor];
          if ([immediateRangeBeaconTimes objectForKey:key] == Nil) {
              if (iBeacon.proximity == CLProximityImmediate) {
                  [immediateRangeBeaconTimes setObject: now forKey:key];
              }
          }
          else {
              if (iBeacon.proximity == CLProximityImmediate) {
                  if ([now timeIntervalSinceDate: [immediateRangeBeaconTimes objectForKey:key]] > 60) {
                      NSLog(@"This beacon has been immediate for 60 seconds.  Do something.");
                  }
              }
              else {
                  [immediateRangeBeaconTimes removeObjectForKey:key];
              }

          }

      }
  }

I realize this is not exactly what you were asking, but wanted to offer an alternative in case it works better for your use case.