DateTime的[上周，上月为一期]

Question

我需要安装上周，在下拉列表改变

上个月期间我做

 switch (DDL.SelectedIndex) 
     { 
      case 0: 
       { 
        // last week 
        this.TextBox3.Text = DateTime. //Previos week first day 
        this.TextBox4.Text = DateTime. //Previos week last day 
       } break; 
      case 1: 
       { 
        // last mouth 
        this.TextBox3.Text = DateTime.// Previos month first day 
        this.TextBox4.Text = DateTime.// Previos month last day 
       } break; 
} 

那么有没有一些方法如何选择日期像我想要的价值？

也，我已经有了文本框

谢谢AJAX日历扩展。

Answer 1

这样的事情，我想：

int dayOfWeekNumber = (int)DateTime.Today.DayOfWeek - (int)CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek; 

var previosWeekFirstDay = DateTime.Today.AddDays(-7 - dayOfWeekNumber); 

var previosWeekLastDay = previosWeekFirstDay.AddDays(6); 

var previosMonthFirstDay = DateTime.Today.AddMonths(-1); 
previosMonthFirstDay = previosMonthFirstDay.AddDays(-previosMonthFirstDay.Day + 1); 

var previosMonthLastDay = previosMonthFirstDay.AddDays(DateTime.DaysInMonth(previosMonthFirstDay.Year, previosMonthFirstDay.Month) - 1); 

编辑：见Fredrik Mörk评论。