Windows.Globalization.Calendar.AddNanoseconds C# (CSharp) Method

		public extern void AddNanoseconds([In] int nanoseconds);
		public extern string NanosecondAsString();

        /// <summary>
        /// Invoked when 'Get History' button is clicked.
        /// Depending on the user selection, this handler uses one of the overloaded
        /// 'GetSystemHistoryAsync' APIs to retrieve the pedometer history of the user
        /// </summary>
        /// <param name="sender">unused</param>
        /// <param name="e">unused</param>
        async private void GetHistory_Click(object sender, Windows.UI.Xaml.RoutedEventArgs e)
        {
            IReadOnlyList<PedometerReading> historyReadings = null;
            DateTimeFormatter timestampFormatter = new DateTimeFormatter("shortdate longtime");

            // Disable subsequent history retrieval while the async operation is in progress
            GetHistory.IsEnabled = false;

            // clear previous content being displayed
            historyRecords.Clear();

            try
            {
                if (getAllHistory)
                {
                    DateTime dt = DateTime.FromFileTimeUtc(0);
                    DateTimeOffset fromBeginning = new DateTimeOffset(dt);
                    rootPage.NotifyUser("Retrieving all available History", NotifyType.StatusMessage);
                    historyReadings = await Pedometer.GetSystemHistoryAsync(fromBeginning);
                }
                else
                {
                    String notificationString = "Retrieving history from: ";
                    Calendar calendar = new Calendar();
                    calendar.ChangeClock("24HourClock");

                    // DateTime picker will also include hour, minute and seconds from the the system time.
                    // Decrement the same to be able to correctly add TimePicker values.

                    calendar.SetDateTime(FromDate.Date);
                    calendar.AddNanoseconds(-calendar.Nanosecond);
                    calendar.AddSeconds(-calendar.Second);
                    calendar.AddMinutes(-calendar.Minute);
                    calendar.AddHours(-calendar.Hour);
                    calendar.AddSeconds(Convert.ToInt32(FromTime.Time.TotalSeconds));

                    DateTimeOffset fromTime = calendar.GetDateTime();

                    calendar.SetDateTime(ToDate.Date);
                    calendar.AddNanoseconds(-calendar.Nanosecond);
                    calendar.AddSeconds(-calendar.Second);
                    calendar.AddMinutes(-calendar.Minute);
                    calendar.AddHours(-calendar.Hour);
                    calendar.AddSeconds(Convert.ToInt32(ToTime.Time.TotalSeconds));

                    DateTimeOffset toTime = calendar.GetDateTime();

                    notificationString += timestampFormatter.Format(fromTime);
                    notificationString += " To ";
                    notificationString += timestampFormatter.Format(toTime);

                    if (toTime.ToFileTime() < fromTime.ToFileTime())
                    {
                        rootPage.NotifyUser("Invalid time span. 'To Time' must be equal or more than 'From Time'", NotifyType.ErrorMessage);

                        // Enable subsequent history retrieval while the async operation is in progress
                        GetHistory.IsEnabled = true;
                    }
                    else
                    {
                        TimeSpan span;
                        span = TimeSpan.FromTicks(toTime.Ticks - fromTime.Ticks);
                        rootPage.NotifyUser(notificationString, NotifyType.StatusMessage);
                        historyReadings = await Pedometer.GetSystemHistoryAsync(fromTime, span);
                    }
                }

                if (historyReadings != null)
                {
                    foreach(PedometerReading reading in historyReadings)
                    {
                        HistoryRecord record = new HistoryRecord(reading);
                        historyRecords.Add(record);
                    }

                    rootPage.NotifyUser("History retrieval completed", NotifyType.StatusMessage);
                }
            }
            catch (UnauthorizedAccessException)
            {
                rootPage.NotifyUser("User has denied access to activity history", NotifyType.ErrorMessage);
            }

            // Finally, re-enable history retrieval
            GetHistory.IsEnabled = true;
        }