C#工具类（二）：对各数据类型Null值的封装

将各数据类型在未赋值情况下使用的默认值，统一封装到一个Null类中。

    /// 

    /// NULL
    /// 
    public class Null
    {
        public static short NullShort
        {
            get
            {
                return -1;
            }
        }

        public static int NullInteger
        {
            get
            {
                return -1;
            }
        }

        public static byte NullByte
        {
            get
            {
                return 255;
            }
        }

        public static float NullSingle
        {
            get
            {
                return float.MinValue;
            }
        }

        public static double NullDouble
        {
            get
            {
                return double.MinValue;
            }
        }

        public static decimal NullDecimal
        {
            get
            {
                return decimal.MinValue;
            }
        }

        public static DateTime NullDate
        {
            get
            {
                return DateTime.MinValue;
            }
        }

        public static string NullString
        {
            get
            {
                return string.Empty;
            }
        }

        public static bool NullBoolean
        {
            get
            {
                return false;
            }
        }

        public static Guid NullGuid
        {
            get
            {
                return Guid.Empty;
            }
        }

        public static object SetNull(PropertyInfo objPropertyInfo)
        {
            object returnValue = null;
            switch (objPropertyInfo.PropertyType.ToString())
            {
                case "System.Int16":
                    returnValue = NullShort;
                    break;
                case "System.Int32":
                case "System.Int64":
                    returnValue = NullInteger;
                    break;
                case "system.Byte":
                    returnValue = NullByte;
                    break;
                case "System.Single":
                    returnValue = NullSingle;
                    break;
                case "System.Double":
                    returnValue = NullDouble;
                    break;
                case "System.Decimal":
                    returnValue = NullDecimal;
                    break;
                case "System.DateTime":
                    returnValue = NullDate;
                    break;
                case "System.String":
                case "System.Char":
                    returnValue = NullString;
                    break;
                case "System.Boolean":
                    returnValue = NullBoolean;
                    break;
                case "System.Guid":
                    returnValue = NullGuid;
                    break;
                default:
                    //Enumerations default to the first entry
                    Type pType = objPropertyInfo.PropertyType;
                    if (pType.BaseType.Equals(typeof(Enum)))
                    {
                        Array objEnumValues = Enum.GetValues(pType);
                        Array.Sort(objEnumValues);
                        returnValue = Enum.ToObject(pType, objEnumValues.GetValue(0));
                    }
                    else //complex object
                    {
                        returnValue = null;
                    }
                    break;
            }
            return returnValue;
        }

        public static bool IsNull(object objField)
        {
            bool isNull = false;
            if (objField != null)
            {
                if (objField is int)
                {
                    isNull = objField.Equals(NullInteger);
                }
                else if (objField is short)
                {
                    isNull = objField.Equals(NullShort);
                }
                else if (objField is byte)
                {
                    isNull = objField.Equals(NullByte);
                }
                else if (objField is float)
                {
                    isNull = objField.Equals(NullSingle);
                }
                else if (objField is double)
                {
                    isNull = objField.Equals(NullDouble);
                }
                else if (objField is decimal)
                {
                    isNull = objField.Equals(NullDecimal);
                }
                else if (objField is DateTime)
                {
                    var objDate = (DateTime)objField;
                    isNull = objDate.Date.Equals(NullDate.Date);
                }
                else if (objField is string)
                {
                    isNull = objField.Equals(NullString);
                }
                else if (objField is bool)
                {
                    isNull = objField.Equals(NullBoolean);
                }
                else if (objField is Guid)
                {
                    isNull = objField.Equals(NullGuid);
                }
                else //complex object
                {
                    isNull = false;
                }
            }
            else
            {
                isNull = true;
            }
            return isNull;
        }
    }