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

		public extern void AddDays([In] int days);
		public extern string DayAsString();

        /// <summary>
        /// This is the click handler for the 'Get Activity History' button.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        async private void ScenarioGetActivityHistory(object sender, RoutedEventArgs e)
        {
            // Reset fields and status
            ScenarioOutput_Count.Text = "No data";
            ScenarioOutput_Activity1.Text = "No data";
            ScenarioOutput_Confidence1.Text = "No data";
            ScenarioOutput_Timestamp1.Text = "No data";
            ScenarioOutput_ActivityN.Text = "No data";
            ScenarioOutput_ConfidenceN.Text = "No data";
            ScenarioOutput_TimestampN.Text = "No data";
            rootPage.NotifyUser("", NotifyType.StatusMessage);

            var calendar = new Calendar();
            calendar.SetToNow();
            calendar.AddDays(-1);
            var yesterday = calendar.GetDateTime();

            // Get history from yesterday onwards
            var history = await ActivitySensor.GetSystemHistoryAsync(yesterday);

            ScenarioOutput_Count.Text = history.Count.ToString();
            if (history.Count > 0)
            {
                var reading1 = history[0];
                ScenarioOutput_Activity1.Text = reading1.Activity.ToString();
                ScenarioOutput_Confidence1.Text = reading1.Confidence.ToString();
                ScenarioOutput_Timestamp1.Text = reading1.Timestamp.ToString("u");

                var readingN = history[history.Count - 1];
                ScenarioOutput_ActivityN.Text = readingN.Activity.ToString();
                ScenarioOutput_ConfidenceN.Text = readingN.Confidence.ToString();
                ScenarioOutput_TimestampN.Text = readingN.Timestamp.ToString("u");
            }
        }