.NET 4.5中的TimeZoneInfo错误

Question

I have recently updated my os with .net 4.5 framework and compiled all my applications using it. unfortunately some of the automatic tests i wrote now fails on the Assert constructions concerning DateTime types.

After a deep analysis i turned out this:

in .net 4.0

DateTime dateUsing40 = new DateTime(2011, 4, 7); // ticks 634377312000000000    
dateUsing40.ToUniversalTime(); //ticks **634377240000000000

bool isDaylightST = dateUsing40.IsDaylightSavingTime(); // returns **true

in .net 4.5

DateTime dateUsing45 = new DateTime(2011, 4, 7); // ticks 634377312000000000
dateUsing45.ToUniversalTime(); //ticks  **634377276000000000    
bool isDaylightST = dateUsing45.IsDaylightSavingTime(); // returns **false

the System.Threading.Thread.CurrentThread.CurrentCulture is in both cases {it-IT}

Actually the date i used is in the range of the (italian but also for all countries that use WET) daylight time so it looks like there is a (huge) bug in the framework. however i didn't find anything useful about.

I verified in both machines:

• regional settings are still set in Italian.
• "Automatically adjust clock for daylight saving changes" is checked.
• opening Regional and settings-> on tab Location -> current location is still Italy.
• os Windows 7 x64

SOLVED:

the framework update changed the DynamicDaylightTimeDisabled's value to 1. To solve this issue it's necessary to turn it to 0 and rebooting. Another way to do it is using the clock UI form.

Answer 1

Check the value of var tziLocal = TimeZoneInfo.Local; (cf. Shaun's answer), and its Id property.

Equivalently (I think), go to PowerShell and write:

Get-ItemProperty HKLM:\SYSTEM\CurrentControlSet\Control\TimeZoneInformation -Name TimeZoneKeyName

and check the value of TimeZoneKeyName winreg "property". Get-ItemProperty can be shortened to just gp .

Based on experimentation, the CurrentCulture , CurrentUICulture and RegionInfo.CurrentRegion are not used, for determining "local time".

Instead if you go to Windows, Control Panel → Clock, Language, and Region → Date and Time → tab Date and Time → section Time zone → button Change time zone... , changing that zone seems to work.

Of course, if Windows registry contains wrong settings for Italy, typically the ID "W. Europe Standard Time" (not "Romance Standard Time" , not "Central European Standard Time" ), on your particular machine, that would be a problem.

Answer 2

How about using the TimeZoneInfo class?

DateTime dateUsing45 = new DateTime(2011, 4, 7); // ticks 634377312000000000
dateUsing45.ToUniversalTime(); //ticks  **634377276000000000    

TimeZoneInfo cstZone = TimeZoneInfo.FindSystemTimeZoneById("Central European Standard Time");
var isDaylightST = cstZone.IsDaylightSavingTime(dateUsing45);