public async Task <string> QueryDateOfBirth()
        {
            NSError error;
            string  resultString = string.Empty;
            await Task.Factory.StartNew(() => resultString = m_healthKitStore.GetDateOfBirth (out error).ToString());

            HealthKitDataContext.ActiveHealthKitData.DateOfBirth = resultString;
            Console.WriteLine(resultString);
            return(resultString);
        }