/// <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( - 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( - datetime.Day).AddMonths().AddDays(-);

}  

/// <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( - datetime.Day).AddMonths(-);

}  

/// <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( - datetime.Day).AddDays(-);

}