C# EmptyValue类代码示例

 /// <summary>
 /// Creates a new SmartDate object.
 /// </summary>
 /// <param name="emptyIsMin">Indicates whether an empty date is the min or max date value.</param>
 public SmartDate(bool emptyIsMin)
 {
   _emptyValue = GetEmptyValue(emptyIsMin);
   _format = null;
   _initialized = false;
   // provide a dummy value to allow real initialization
   _date = DateTime.MinValue;
   SetEmptyDate(_emptyValue);
 }

        /// <summary>
        /// 创建SmartDate的实例
        /// </summary>
        /// <param name="emptyIsMin">空日期是否转换成最小日期</param>
        public SmartDate(bool emptyIsMin)
        {
            //将空日期的布尔标识转成枚举标识
            _emptyValue = GetEmptyValue(emptyIsMin);

            //设置格式字符串
            _format = null;

            //设置初始化标识
            _initialized = false;

            //将日期最小值赋给日期字段
            _date = _minDate;

            //设置空日期
            SetEmptyDate(_emptyValue);
        }

 /// <summary>
 /// 为空日期赋值
 /// </summary>
 /// <param name="emptyValue">空日期的类型</param>
 private void SetEmptyDate(EmptyValue emptyValue)
 {
     if (emptyValue == EmptyValue.MinDate)
     {
         this.Date = _minDate;
     }
     else
     {
         this.Date = DateTime.MaxValue;
     }
 }

 /// <summary>
 /// Converts a text date representation into a Date value.
 /// </summary>
 /// <remarks>
 /// An empty string is assumed to represent an empty date. An empty date
 /// is returned as the MinValue or MaxValue of the Date datatype depending
 /// on the EmptyIsMin parameter.
 /// </remarks>
 /// <param name="value">The text representation of the date.</param>
 /// <param name="emptyValue">Indicates whether an empty date is the min or max date value.</param>
 /// <returns>A Date value.</returns>
 public static DateTime StringToDate(string value, EmptyValue emptyValue)
 {
   DateTime result = DateTime.MinValue;
   if (TryStringToDate(value, emptyValue, ref result))
     return result;
   else
     throw new ArgumentException(Resources.StringToDateException);
 }

 /// <summary>
 /// Converts a string value into a SmartDate.
 /// </summary>
 /// <param name="value">String containing the date value.</param>
 /// <param name="emptyValue">Indicates whether an empty date is the min or max date value.</param>
 /// <returns>A new SmartDate containing the date value.</returns>
 public static SmartDate Parse(string value, EmptyValue emptyValue)
 {
   return new SmartDate(value, emptyValue);
 }

        /// <summary>
        /// 将DateTime类型日期转换为指定格式的字符串
        /// </summary>
        /// <param name="value">要转换的日期</param>
        /// <param name="formatString">格式字符串</param>
        /// <param name="emptyValue">空日期的取值类型</param>        
        public static string DateToString(DateTime value, string formatString, EmptyValue emptyValue)
        {
            //如果日期为最大日期或最小日期，则转换为空字符串
            if (emptyValue == EmptyValue.MinDate)
            {
                if (value == _minDate)
                {
                    return string.Empty;
                }
            }
            else
            {
                if (value == DateTime.MaxValue)
                {
                    return string.Empty;
                }
            }

            //将日期以指定格式的字符串返回
            return string.Format("{0:" + formatString + "}", value);
        }

 /// <summary>
 /// 将字符串转换为SmartDate类型,可指定空日期的取值类型
 /// </summary>
 /// <param name="date">字符串形式的日期</param>
 /// <param name="emptyDateType">空日期的取值类型</param>        
 public static SmartDate Parse(string date, EmptyValue emptyDateType)
 {
     return new SmartDate(date, emptyDateType);
 }

        /// <summary>
        /// 将字符串转换为DateTime类型日期
        /// </summary>
        /// <param name="value">日期字符串</param>
        /// <param name="emptyValue">空日期的取值类型</param>        
        public static DateTime StringToDate(string value, EmptyValue emptyValue)
        {
            //要返回的的日期
            DateTime result = _minDate;

            //如果string成功转换为DateTime，则返回
            if (TryStringToDate(value, emptyValue, ref result))
            {
                return result;
            }
            else
            {
                //转换失败，抛出异常
                throw new ArgumentException(SmartDateString.StringToDateException);
            }
        }

        /// <summary>
        /// 判断字符串是否能转换为一个SmartDate日期,并返回转换成功后的日期
        /// </summary>
        /// <param name="value">要转换的日期字符串</param>
        /// <param name="emptyValue">空日期的取值类型</param>
        /// <param name="result">返回转换成功后的日期</param>        
        public static bool TryParse(string value, EmptyValue emptyValue, ref SmartDate result)
        {
            //定义用于存储日期字符串转换的DateTime日期
            DateTime dateResult = _minDate;

            //将日期字符串转换为DateTime日期
            if (TryStringToDate(value, emptyValue, ref dateResult))
            {
                //如果转换成功，则返回该日期的SmartDate类型
                result = new SmartDate(dateResult, emptyValue);

                return true;
            }
            else
            {
                return false;
            }
        }

 private void SetEmptyDate(EmptyValue emptyValue)
 {
   if (emptyValue == SmartDate.EmptyValue.MinDate)
     this.Date = DateTime.MinValue;
   else
     this.Date = DateTime.MaxValue;
 }

        /// <summary>
        /// 判断字符串是否能转换为一个Datetime日期,并返回转换成功后的日期
        /// </summary>
        /// <param name="value">要转换的日期字符串</param>
        /// <param name="emptyValue">空日期的取值类型</param>
        /// <param name="result">返回转换成功后的日期</param>        
        private static bool TryStringToDate(string value, EmptyValue emptyValue, ref DateTime result)
        {
            //定义一个临时日期
            DateTime temp;

            #region 如果日期字符串为空，则转成最大或最小的日期
            if (string.IsNullOrEmpty(value))
            {
                //如果空日期的取值类型为MinDate,则转成最小日期,否则最大日期
                if (emptyValue == EmptyValue.MinDate)
                {
                    result = _minDate;
                }
                else
                {
                    result = DateTime.MaxValue;
                }

                //返回true
                return true;
            }
            #endregion

            #region 将日期字符串转换为DateTime
            if (DateTime.TryParse(value, out temp))
            {
                //如果转换成功，则返回true
                result = temp;
                return true;
            }
            #endregion

            #region 如果日期字符串是自定义的值，则进行转换
            //将日期字符串转成大写
            string date = value.Trim().ToLower();
            //转换成今天的日期
            if (date == SmartDateString.SmartDateT || date == SmartDateString.SmartDateToday || date == ".")
            {
                result = DateTime.Now;
                return true;
            }
            //转换成昨天的日期
            if (date == SmartDateString.SmartDateY || date == SmartDateString.SmartDateYesterday || date == "-")
            {
                result = DateTime.Now.AddDays(-1);
                return true;
            }
            //转换成明天的日期
            if (date == SmartDateString.SmartDateTom || date == SmartDateString.SmartDateTomorrow || date == "+")
            {
                result = DateTime.Now.AddDays(1);
                return true;
            }
            #endregion

            //转换失败，返回false
            return false;
        }

 /// <summary>
 /// Converts a string value into a SmartDate.
 /// </summary>
 /// <param name="value">String containing the date value.</param>
 /// <param name="emptyValue">Indicates whether an empty date is the min or max date value.</param>
 /// <param name="result">The resulting SmartDate value if the parse was successful.</param>
 /// <returns>A value indicating if the parse was successful.</returns>
 public static bool TryParse(string value, EmptyValue emptyValue, ref SmartDate result)
 {
   System.DateTime dateResult = DateTime.MinValue;
   if (TryStringToDate(value, emptyValue, ref dateResult))
   {
     result = new SmartDate(dateResult, emptyValue);
     return true;
   }
   else
   {
     return false;
   }
 }

    private static bool TryStringToDate(string value, EmptyValue emptyValue, ref DateTime result)
    {
      // call custom parser if set...
      if (_customParser != null)
      {
        var tmpValue = _customParser.Invoke(value);
        // i f custom parser returned a value then parsing succeeded
        if (tmpValue.HasValue)
        {
          result = tmpValue.Value;
          return true;
        }
      }

      DateTime tmp;
      if (String.IsNullOrEmpty(value))
      {
        result = emptyValue == EmptyValue.MinDate ? DateTime.MinValue : DateTime.MaxValue;
        return true;
      }
      if (DateTime.TryParse(value, out tmp))
      {
        result = tmp;
        return true;
      }
      

      string ldate = value.Trim().ToLower();
      if (ldate == Resources.SmartDateT ||
          ldate == Resources.SmartDateToday ||
          ldate == ".")
      {
        result = DateTime.Now;
        return true;
      }
      if (ldate == Resources.SmartDateY ||
          ldate == Resources.SmartDateYesterday ||
          ldate == "-")
      {
        result = DateTime.Now.AddDays(-1);
        return true;
      }
      if (ldate == Resources.SmartDateTom ||
          ldate == Resources.SmartDateTomorrow ||
          ldate == "+")
      {
        result = DateTime.Now.AddDays(1);
        return true;
      }

      return false;
    }

 void IMobileObject.SetState(SerializationInfo info)
 {
   _date = info.GetValue<DateTime>("SmartDate._date");
   _defaultFormat = info.GetValue<string>("SmartDate._defaultFormat");
   _emptyValue = (EmptyValue)System.Enum.Parse(typeof(EmptyValue), info.GetValue<string>("SmartDate._emptyValue"), true);
   _format = info.GetValue<string>("SmartDate._format");
   _initialized = info.GetValue<bool>("SmartDate._initialized");
 }

 /// <summary>
 /// Converts a date value into a text representation.
 /// </summary>
 /// <remarks>
 /// Whether the date value is considered empty is determined by
 /// the EmptyIsMin parameter value. If the date is empty, this
 /// method returns an empty string. Otherwise it returns the date
 /// value formatted based on the FormatString parameter.
 /// </remarks>
 /// <param name="value">The date value to convert.</param>
 /// <param name="formatString">The format string used to format the date into text.</param>
 /// <param name="emptyValue">Indicates whether an empty date is the min or max date value.</param>
 /// <returns>Text representation of the date value.</returns>
 public static string DateToString(
   DateTime value, string formatString, EmptyValue emptyValue)
 {
   if (emptyValue == EmptyValue.MinDate)
   {
     if (value == DateTime.MinValue)
       return string.Empty;
   }
   else
   {
     if (value == DateTime.MaxValue)
       return string.Empty;
   }
   return string.Format("{0:" + formatString + "}", value);
 }