使用 DotNet 在本地一天中的小时数

Question

dotnet 中是否有任何内置的 api 可以告诉您指定的一天有多少小时？

这假设 API 将在给定时区享受夏令时。因此，对于从格林威治标准时间进入夏令时的英国，白天将有 23 小时，夏令时将有 25 小时回到格林威治标准时间。

我还没有在 nodatime 中发现任何可以直接执行此操作的东西。

我可以在NodaTime中做类似下面的事情，但是有没有更好的方法？

DateTimeZone london = DateTimeZoneProviders.Tzdb["Europe/London"];
LocalDate start = new LocalDate(2021, 3, 28);
LocalDate end = new LocalDate(2021, 3, 29);

ZonedDateTime startZ = london.AtStartOfDay(start);
ZonedDateTime endZ = london.AtStartOfDay(end);
ZonedDateTime dt = startZ;

int period = 1;

while (dt.ToInstant() < endZ.ToInstant())
{
    testOutputHelper.WriteLine("Period: " + period + ", " + dt.ToString() + ", Hour: " + dt.Hour);
    
    dt = dt.PlusHours(1);
    period++;
}

Answer 1

是的，在野田时代你绝对可以做到更简单：

public static Duration GetDayDuration(LocalDate date, DateTimeZone zone)
{
    var start = zone.AtStartOfDay(date);
    var end = zone.AtStartOfDay(date.PlusDays(1));
    return end - start;
}

那将return一个Duration，这是“经过的时间量”的野田时间表示法。您可以使用其中的 TotalHours 属性。（使用 Hours 是错误的，因为 25 小时的持续时间对于 Hours 属性来说 return 1。）

完整示例：

using NodaTime;
using System;

class Test
{
    static void Main()
    {
        DateTimeZone london = DateTimeZoneProviders.Tzdb["Europe/London"];
        ShowDayDuration(new LocalDate(2021, 3, 28), london);
        ShowDayDuration(new LocalDate(2021, 6, 19), london);
        ShowDayDuration(new LocalDate(2021, 10, 31), london);
    }
    
    public static void ShowDayDuration(LocalDate date, DateTimeZone zone)
    {
        var duration = GetDayDuration(date, zone);
        // Note: this truncation will give the result in rare cases,
        // when the UTC offset changes by a fractional number of hours.
        int hours = (int) duration.TotalHours;
        Console.WriteLine($"Duration of {date} in zone {zone.Id}: {hours} hours");
    }

    public static Duration GetDayDuration(LocalDate date, DateTimeZone zone)
    {
        var start = zone.AtStartOfDay(date);
        var end = zone.AtStartOfDay(date.PlusDays(1));
        return end.ToInstant() - start.ToInstant();
    }
}

Answer 2

Jon 的回答很棒，展示了 Noda Time 如何简化此类操作。

但是，由于该问题还询问了有关内置 API 的问题，为了完整起见，我将展示一种不需要 Noda Time 的替代方法。

using System;
using System.Diagnostics;
using System.Linq;
using System.Runtime.InteropServices;
                    
public class Program
{
    public static void Main()
    {
        // Note, the following line is just an example for clarity.  If you know which form of identifier your platform supports
        // or are using TimeZoneConverter, or are using .NET 6+ (which will have conversions built-in), then you can just use the appropriate simple string.
        string tzid = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "GMT Standard Time" : "Europe/London";
        
        // Get the time zone and show a few different days and their duration.
        TimeZoneInfo zone = TimeZoneInfo.FindSystemTimeZoneById(tzid);
        ShowDayDuration(new DateTime(2021, 3, 28), zone);
        ShowDayDuration(new DateTime(2021, 6, 19), zone);
        ShowDayDuration(new DateTime(2021, 10, 31), zone);
    }
    
    public static void ShowDayDuration(DateTime date, TimeZoneInfo zone)
    {
        TimeSpan duration = GetDayDuration(date, zone);
        Console.WriteLine($"Duration of {date:yyyy-MM-dd} in zone {zone.Id}: {duration.TotalHours} hours");
    }
    
    public static TimeSpan GetDayDuration(DateTime date, TimeZoneInfo zone)
    {
        // Just to make sure the input value is strictly a date with the time truncated.
        Debug.Assert(date.Kind == DateTimeKind.Unspecified);
        Debug.Assert(date.TimeOfDay == TimeSpan.Zero);
        
        // Subtract the start of the given date and the subsequent date.
        DateTimeOffset dto1 = GetStartOfDay(date, zone);
        DateTimeOffset dto2 = GetStartOfDay(date.AddDays(1), zone);
        return dto2 - dto1;
    }
    
    public static DateTimeOffset GetStartOfDay(DateTime date, TimeZoneInfo zone)
    {
        // Just to make sure the input value is strictly a date with the time truncated.
        Debug.Assert(date.Kind == DateTimeKind.Unspecified);
        Debug.Assert(date.TimeOfDay == TimeSpan.Zero);
        
        TimeSpan offset;        
        if (zone.IsAmbiguousTime(date))
        {
            // When the date/time is ambiguous, use the larger of the two offsets because the resulting value will come first sequentially.
            offset = zone.GetAmbiguousTimeOffsets(date).Max();
        }
        else
        {
            // When the date/time is invalid, find the next valid time.  Search by 15 minute increments to accomodate oddities of various time zones.
            while (zone.IsInvalidTime(date))
            {
                date = date.AddMinutes(15);
            }

            offset = zone.GetUtcOffset(date);
        }
        
        return new DateTimeOffset(date, offset);
    }
}

Working fiddle here.

输出：

Duration of 2021-03-28 in zone Europe/London: 23 hours
Duration of 2021-06-19 in zone Europe/London: 24 hours
Duration of 2021-10-31 in zone Europe/London: 25 hours

如您所见，Noda Time 的类型系统和内置的 AtStartOfDay 方法使 Noda Time 成为一个更简单的选项，但仍然可以仅使用内置类型来获得正确答案。

使用 DotNet 在本地一天中的小时数

Hours in Day Locally using DotNet

.net

datetime

nodatime