WinForm------DateTime获取月第一天和最后一天取法

http://blog.csdn.net/livening/article/details/6049341/

/// <summary>  
/// 取得某月的第一天  
/// </summary>  
/// <param name="datetime">要取得月份第一天的时间</param>  
/// <returns></returns>  
private DateTime FirstDayOfMonth(DateTime datetime)  
{  
    return datetime.AddDays(1 - datetime.Day);  
}  
  
/**//// <summary>  
/// 取得某月的最后一天  
/// </summary>  
/// <param name="datetime">要取得月份最后一天的时间</param>  
/// <returns></returns>  
private DateTime LastDayOfMonth(DateTime datetime)  
  
    return datetime.AddDays(1 - datetime.Day).AddMonths(1).AddDays(-1);  
}  
  
/**//// <summary>  
/// 取得上个月第一天  
/// </summary>  
/// <param name="datetime">要取得上个月第一天的当前时间</param>  
/// <returns></returns>  
private DateTime FirstDayOfPreviousMonth(DateTime datetime)  
{  
    return datetime.AddDays(1 - datetime.Day).AddMonths(-1);  
}  
  
/**//// <summary>  
/// 取得上个月的最后一天  
/// </summary>  
/// <param name="datetime">要取得上个月最后一天的当前时间</param>  
/// <returns></returns>  
private DateTime LastDayOfPrdviousMonth(DateTime datetime)  
{  
    return datetime.AddDays(1 - datetime.Day).AddDays(-1);  
}