Issue of Reading and Converting Date of Google Calendar Events when language is set to Arabic in C# - c#-4.0

Question

I am Using Google APis .net client library to read calendar events.
I have following line of code
newRow["Start"] = pEventItem.Start.DateTime.HasValue ?
Convert.ToDateTime(pEventItem.Start.DateTime) : Convert.ToDateTime(pEventItem.Start.Date);
Where PEventItem is of type Google.Apis.Calendar.v3.Data.Event and NewRow[...] is of type DataRow. The Value of pEventItem.Start.Date is "2019-06-24" (as seen in debug window)
The above line of code works perfect, But fails when UI language / Culture is set to Arabic (SaudiArabia) The same Convert.ToDateTime throws error "String was not recognized as a valid DateTime".
btw, How i am changing the UI language is as below for your information.
Thread.CurrentThread.CurrentCulture = System.Globalization.CultureInfo.GetCultureInfo(ChangeLanguageTo);
Thread.CurrentThread.CurrentUICulture = System.Globalization.CultureInfo.GetCultureInfo(ChangeLanguageTo);
I tried to set 2nd parameter of the Convert.ToDateTime function in an hope that it will convert date correctly...
CultureInfo enUsCulture = new CultureInfo("en-us");
newRow["Start"] = pEventItem.Start.DateTime.HasValue ? Convert.ToDateTime(pEventItem.Start.DateTime, enUsCulture) : Convert.ToDateTime(pEventItem.Start.Date, enUsCulture);
Well Now it does not throw exception, but the returned date is incorrect. value retuned is {21/10/40 12:00:00 ص}
while The actual date pEventItem.Start.Date is "2019-06-24"
I also tried invariant culture also, but result is same, converted date is wrong. What could be the issue?
Regards

Answer 1

There are a few things going on here.
Firstly, if you use EventDateTime.DateTime (e.g. via pEventItem.Start.DateTime) you don't need to call Convert.ToDateTime, because that's already a DateTime?... you can just take the Value property to get a DateTime from a DateTime?. However, I should warn that that can perform time zone conversions that you may not want. (We can't fix the library to avoid those, as it would be a breaking change.) Instead, you may want to parse EventDateTime.DateTimeRaw, which is the original string value returned by the API.
When parsing, I'd suggest using the invariant culture using CultureInfo.InvariantCulture (instead of creating an en-US culture), and parse using DateTime.ParseExact, specifying the format you expect based on whether you're parsing a date or a full date/time.
In terms of "the returned date is incorrect" - I believe that's really just the formatted value that's using the default culture, including the calendar system. We can see that at play in the code below, which constructs the DateTime directly (so can't be affected by any text parsing etc). When formatted using the invariant culture, it shows as 2019-06-24, but when formatted with ar-SA, it shows as "1440-10-21" due to the default calendar system for that culture being System.Globalization.UmAlQuraCalendar:
// Note: when a calendar system is not specified,
// it's implicitly Gregorian.
DateTime date = new DateTime(2019, 6, 24);
Console.WriteLine(date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture));
Console.WriteLine(date.ToString("yyyy-MM-dd", new CultureInfo("ar-SA")));
So what you're seeing in the debugger is the correct date - but formatted in a way you weren't expecting.