使用Noda Time C＃时获得无效结果

Question

Assume Instant variable contains "4/8/2014 11:09:24 AM" when i pass this value to this method it gives me an output "4/8/2014 12:09:24 PM" i checked in some time zone calcluator plus in oracle i should be getting "4/8/2014 04:09:24 PM" or "4/8/2014 16:09:24 PM" depending on hour format. why is it not converting into proper time format?

public static string ConvertDateTimeToUserTimeZone()
{
    DateTime dt = DateTime.Parse("4/8/2014 11:09:24 AM");
    Instant now = Instant.FromDateTimeUtc(DateTime.SpecifyKind(dt,DateTimeKind.Utc));
    DateTimeZone dtZone = DateTimeZoneProviders.Tzdb["Europe/London"];
    ZonedDateTime zdt = now.InZone(dtZone);
    return zdt.ToDateTimeOffset().ToString("G");
}

Answer 1

Reading through your comments, it would appear that you'd like to do the following:

• Parse the input string
• Assign it to the the US Eastern time zone ( "America/New_York" )
• Convert it to the time zone for the UK ( "Europe/London" )
• Format it as a string in the general format

I will show using Noda Time for all of these steps, rather than mixing in non-Noda mechanisms.

var generalPattern = LocalDateTimePattern.CreateWithCurrentCulture("G");

string inputString = "4/8/2014 11:09:24 AM";
string sourceTimeZone = "America/New_York";
string targetTimeZone = "Europe/London";

LocalDateTime ldt1 = generalPattern.Parse(inputString).Value;
DateTimeZone tz1 = DateTimeZoneProviders.Tzdb[sourceTimeZone];
ZonedDateTime zdt1 = ldt1.InZoneLeniently(tz1);

DateTimeZone tz2 = DateTimeZoneProviders.Tzdb[targetTimeZone];
ZonedDateTime zdt2 = zdt1.WithZone(tz2);
LocalDateTime ldt2 = zdt2.LocalDateTime;

string output = generalPattern.Format(ldt2);

Notice that I used CreateWithCurrentCulture when setting up the pattern. This assumes you mean to use whatever the current culture is for the machine the code is running on. If that's not the case, then you should set a specific culture instead. This is important when you realize that users in the US will use M/D/Y formatting, while users in the UK will use D/M/Y formatting. This applies to both dates regardless of time zone. (In other words, 4/8/2014 could be April 8th, or August 4th).

Also notice that I used InZoneLeniently when applying the source time zone. This has lenient behavior when it comes to ambiguous and invalid input values due to DST transitions . If you want different behavior, then you might instead use InZoneStrictly , or use InZone and provide your own algorithm.

And finally, it should be noted that I inferred from your comments that you were sourcing these from the US Eastern time zone, which would be either EDT or EST depending on what time of year it is. If you actually meant that the values were always EDT, even when EST is the norm, then you would do the following:

DateTimeZone tz1 = DateTimeZone.ForOffset(Offset.FromHours(-4));

Answer 2

The value you got back from the method is in fact correct.

Let's break it down using LINQPad :

void Main()
{
    var t = new DateTime(2014, 8, 4, 11, 09, 24, DateTimeKind.Utc);
    var i = Instant.FromDateTimeUtc(t);
    var s = ConvertDateTimeToUserTimeZone(i);
    s.Dump("User time zone value");
}

public static string ConvertDateTimeToUserTimeZone(Instant now)
{
    DateTimeZone dtZone = DateTimeZoneProviders.Tzdb["Europe/London"];
    dtZone.GetUtcOffset(now).Dump("TZ at instant");
    ZonedDateTime zdt = now.InZone(dtZone);
    return zdt.ToDateTimeOffset().ToString("G");
}

Output:

TZ at instant 
+01 

User time zone value 
04.08.2014 12:09:24 

The time zone at the point of that instant is thus UTC+1, which means that the value you gave the code gives you the correct value back, 12:09.

To get 16:09, you would need UTC+5, and Europe/London has never been that value.

So 12:09:24 is correct, your assumptions that it should be 16:09:24 is wrong.

You need to go back to the code and/or sites you used to get the "correct" value, the source of your confusion is there, not in this code.