我自己一直在研究这个,并被定向到这里。我个人很想选择选项二,因为替代方案很混乱。Ronnie 的版本很好,但遗憾的是没有考虑不同 FirstDayOfWeeks 的文化。
使用 Reflector,我们可以看到它是如何在内部完成的:
...
DateTime visibleDate = this.EffectiveVisibleDate();
DateTime firstDay = this.FirstCalendarDay(visibleDate);
...
private System.Globalization.Calendar threadCalendar =
DateTimeFormatInfo.CurrentInfo.Calendar;
private DateTime EffectiveVisibleDate()
{
DateTime visibleDate = this.VisibleDate;
if (visibleDate.Equals(DateTime.MinValue))
{
visibleDate = this.TodaysDate;
}
if (this.IsMinSupportedYearMonth(visibleDate))
{
return this.minSupportedDate;
}
return this.threadCalendar.AddDays(visibleDate,
-(this.threadCalendar.GetDayOfMonth(visibleDate) - 1));
}
private DateTime FirstCalendarDay(DateTime visibleDate)
{
DateTime date = visibleDate;
if (this.IsMinSupportedYearMonth(date))
{
return date;
}
int num = ((int)
this.threadCalendar.GetDayOfWeek(date)) - this.NumericFirstDayOfWeek();
if (num <= 0)
{
num += 7;
}
return this.threadCalendar.AddDays(date, -num);
}
private int NumericFirstDayOfWeek()
{
if (this.FirstDayOfWeek != FirstDayOfWeek.Default)
{
return (int) this.FirstDayOfWeek;
}
return (int) DateTimeFormatInfo.CurrentInfo.FirstDayOfWeek;
}
private bool IsMinSupportedYearMonth(DateTime date)
{
return this.IsTheSameYearMonth(this.minSupportedDate, date);
}
private bool IsTheSameYearMonth(DateTime date1, DateTime date2)
{
return (((this.threadCalendar.GetEra(date1) ==
this.threadCalendar.GetEra(date2)) &&
(this.threadCalendar.GetYear(date1) ==
this.threadCalendar.GetYear(date2))) &&
(this.threadCalendar.GetMonth(date1) ==
this.threadCalendar.GetMonth(date2)));
}
可悲的是,该功能已经存在,我们只是无法获得它!