如何在 UWP 平台中使用 ToOADate 函数将 DateTime 值转换为 OADate 格式？

Question

我在 WPF 和 WinForms 平台中使用 DateTime.FromOADate() 和 DateTime.ToOADate() 函数将 DateTime 值转换为 OADate 格式。但是哪些功能在 UWP 平台上不可用。所以任何人都可以提出你的意见，在 UWP 平台中将 dateTime 值转换为 OADate 格式。

Answer 1

UWP平台如何使用ToOADate函数将DateTime值转换为OADate格式？

您可以通过引用.Net reference source 来编写自己的ToOADate 方法。比如下面是ToOADate和FromOADate函数的简单demo，你可以测试一下。

private void btndatetime_Click(object sender, RoutedEventArgs e)
{
    DateTime fromOA = FromOAdate(40967.6424503935);
    System.Diagnostics.Debug.WriteLine(fromOA);
    double toOA = ToOAdate(fromOA);
    System.Diagnostics.Debug.WriteLine(toOA);
}
public DateTime FromOAdate(double oadate)
{
    return new DateTime(DoubleDateToTicks(oadate), DateTimeKind.Unspecified);
} 
public double ToOAdate(DateTime datetime)
{
    return TicksToOADate(datetime.Ticks);
}
private const long TicksPerMillisecond = 10000;
private const long TicksPerSecond = TicksPerMillisecond * 1000;
private const long TicksPerMinute = TicksPerSecond * 60;
private const long TicksPerHour = TicksPerMinute * 60;
private const long TicksPerDay = TicksPerHour * 24;
private const UInt64 TicksMask = 0x3FFFFFFFFFFFFFFF;
private const long DoubleDateOffset = DaysTo1899 * TicksPerDay;
// Number of days in a non-leap year
private const int DaysPerYear = 365;
// Number of days in 4 years
private const int DaysPer4Years = DaysPerYear * 4 + 1;       // 1461
// Number of days in 100 years
private const int DaysPer100Years = DaysPer4Years * 25 - 1;  // 36524
// Number of days in 400 years
private const int DaysPer400Years = DaysPer100Years * 4 + 1; // 146097
private const int DaysTo1899 = DaysPer400Years * 4 + DaysPer100Years * 3 - 367;
// Number of milliseconds per time unit
private const int MillisPerSecond = 1000;
private const int MillisPerMinute = MillisPerSecond * 60;
private const int MillisPerHour = MillisPerMinute * 60;
private const int MillisPerDay = MillisPerHour * 24;
private static double TicksToOADate(long value)
{
    if (value == 0)
        return 0.0;  // Returns OleAut's zero'ed date value.
    if (value < TicksPerDay) // This is a fix for VB. They want the default day to be 1/1/0001 rathar then 12/30/1899.
        value += DoubleDateOffset; // We could have moved this fix down but we would like to keep the bounds check.          
    long millis = (value - DoubleDateOffset) / TicksPerMillisecond;
    if (millis < 0)
    {
        long frac = millis % MillisPerDay;
        if (frac != 0) millis -= (MillisPerDay + frac) * 2;
    }
    return (double)millis / MillisPerDay;
}
internal static long DoubleDateToTicks(double value)
{
    // The check done this way will take care of NaN
    //if (!(value < OADateMaxAsDouble) || !(value > OADateMinAsDouble))
    //    throw new ArgumentException(Environment.GetResourceString("Arg_OleAutDateInvalid"));
    // Conversion to long will not cause an overflow here, as at this point the "value" is in between OADateMinAsDouble and OADateMaxAsDouble
    long millis = (long)(value * MillisPerDay + (value >= 0 ? 0.5 : -0.5));
    // The interesting thing here is when you have a value like 12.5 it all positive 12 days and 12 hours from 01/01/1899
    // However if you a value of -12.25 it is minus 12 days but still positive 6 hours, almost as though you meant -11.75 all negative
    // This line below fixes up the millis in the negative case
    if (millis < 0)
    {
        millis -= (millis % MillisPerDay) * 2;
    }

    millis += DoubleDateOffset / TicksPerMillisecond;
    //if (millis < 0 || millis >= MaxMillis) throw new ArgumentException(Environment.GetResourceString("Arg_OleAutDateScale"));
    return millis * TicksPerMillisecond;
}