c#中 时间格式化

 一、//格式化为DateTime
                nowdate = nowdate.Substring(0, 4) + "-" + nowdate.Substring(4, 2) + "-" + nowdate.Substring(6, 2)        + " "  + nowdate.Substring(8, 2) + ":" + nowdate.Substring(10, 2) + ":" + nowdate.Substring(12, 2);

                DateTime DTnowdate = Convert.ToDateTime(nowdate);
二、
          把字符串20160620093031转换成2016/6/20 9:30:31
           string TarStr = "yyyyMMddHHmmss";  //注意这里用到HH
            IFormatProvider format = new System.Globalization.CultureInfo("zh-CN");
            DateTime MyDate = DateTime.ParseExact(datetime, TarStr, format);