Observe iOS network change

ObserveNetworkChange.m

CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(), //center
                                NULL, // observer
                                onNotifyCallback, // callback
                                CFSTR("com.apple.system.config.network_change"), // event name
                                NULL, // object
                                CFNotificationSuspensionBehaviorDeliverImmediately);

static void onNotifyCallback(CFNotificationCenterRef center, void *observer, CFStringRef name, const void *object, CFDictionaryRef userInfo)
{
    NSString* notifyName = (NSString*)name;
    // this check should really only be necessary if you reuse this one callback method
    //  for multiple Darwin notification events
    if ([notifyName isEqualToString:@"com.apple.system.config.network_change"]) {
        // use the Captive Network API to get more information at this point
        //  http://stackoverflow.com/a/4714842/119114
    } else {
        NSLog(@"intercepted %@", notifyName);
    }
}