gistfile1.m

- (BOOL)isNetworkActivityIndicatorVisible {
    return _activityCount > 0;
}

- (void)incrementActivityCount {
    [self willChangeValueForKey:@"activityCount"];
    OSAtomicIncrement32((int32_t*)&_activityCount);
    [self didChangeValueForKey:@"activityCount"];
}

- (void)decrementActivityCount {
    [self willChangeValueForKey:@"activityCount"];
    OSAtomicDecrement32((int32_t*)&_activityCount);
    [self didChangeValueForKey:@"activityCount"];
}

+ (NSSet *)keyPathsForValuesAffectingIsNetworkActivityIndicatorVisible {
    return [NSSet setWithObject:@"activityCount"];
}