test

NSURLSession do completionHandler:^(NSData *JSONdata, NSURLResponse *response, NSError *error) {
        //various codes to get the JSON response....

        dispatch_async(dispatch_get_main_queue(), ^{
            currentImageOnServerString = fileName
            [self runTheFileComparison]
                });

-(void) runTheFileComparison {
    if (downloadedImageOnDevice != currentImageOnServer) {
        [self removeFileInCalendarFolder];
             [self downloadCalendarImage];
    }
}