class/corlib/System/DBNull.cs

   1 //
   2 // System.DBNull.cs
   3 //
   4 // Authors:
   5 //   Duncan Mak (duncan@ximian.com)
   6 //   Ben Maurer (bmaurer@users.sourceforge.net)
   7 //
   8 // (C) 2002 Ximian, Inc. http://www.ximian.com
   9 // (C) 2003 Ben Maurer
  10 //
  11
  12 //
  13 // Copyright (C) 2004 Novell, Inc (http://www.novell.com)
  14 //
  15 // Permission is hereby granted, free of charge, to any person obtaining
  16 // a copy of this software and associated documentation files (the
  17 // "Software"), to deal in the Software without restriction, including
  18 // without limitation the rights to use, copy, modify, merge, publish,
  19 // distribute, sublicense, and/or sell copies of the Software, and to
  20 // permit persons to whom the Software is furnished to do so, subject to
  21 // the following conditions:
  22 //
  23 // The above copyright notice and this permission notice shall be
  24 // included in all copies or substantial portions of the Software.
  25 //
  26 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  27 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  28 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  29 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  30 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  31 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  32 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  33 //
  34
  35 using System.Runtime.Serialization;
  36 using System.Runtime.InteropServices;
  37
  38 namespace System
  39 {
  40         [Serializable]
  41         [ComVisible (true)]
  42         public sealed class DBNull : ISerializable, IConvertible
  43         {
  44                 // Fields
  45                 public static readonly DBNull Value = new DBNull ();
  46
  47                 // Private constructor
  48                 private DBNull ()
  49                 {
  50                 }
  51
  52                 private DBNull (SerializationInfo info, StreamingContext context)
  53                 {
  54                         throw new NotSupportedException ();
  55                 }
  56
  57                 // Methods
  58                 public void GetObjectData (SerializationInfo info, StreamingContext context)
  59                 {
  60                         UnitySerializationHolder.GetDBNullData (this, info, context);
  61                 }
  62
  63                 public TypeCode GetTypeCode ()
  64                 {
  65                         return TypeCode.DBNull;
  66                 }
  67
  68                 bool IConvertible.ToBoolean (IFormatProvider provider)
  69                 {
  70                         throw new InvalidCastException ();
  71                 }
  72
  73                 byte IConvertible.ToByte (IFormatProvider provider)
  74                 {
  75                         throw new InvalidCastException ();
  76                 }
  77
  78                 char IConvertible.ToChar (IFormatProvider provider)
  79                 {
  80                         throw new InvalidCastException ();
  81                 }
  82
  83                 DateTime IConvertible.ToDateTime (IFormatProvider provider)
  84                 {
  85                         throw new InvalidCastException ();
  86                 }
  87
  88                 decimal IConvertible.ToDecimal (IFormatProvider provider)
  89                 {
  90                         throw new InvalidCastException ();
  91                 }
  92
  93                 double IConvertible.ToDouble (IFormatProvider provider)
  94                 {
  95                         throw new InvalidCastException ();
  96                 }
  97
  98                 short IConvertible.ToInt16 (IFormatProvider provider)
  99                 {
 100                         throw new InvalidCastException ();
 101                 }
 102
 103                 int IConvertible.ToInt32 (IFormatProvider provider)
 104                 {
 105                         throw new InvalidCastException ();
 106                 }
 107
 108                 long IConvertible.ToInt64 (IFormatProvider provider)
 109                 {
 110                         throw new InvalidCastException ();
 111                 }
 112
 113                 sbyte IConvertible.ToSByte (IFormatProvider provider)
 114                 {
 115                         throw new InvalidCastException ();
 116                 }
 117
 118                 float IConvertible.ToSingle (IFormatProvider provider)
 119                 {
 120                         throw new InvalidCastException ();
 121                 }
 122
 123                 object IConvertible.ToType (Type targetType, IFormatProvider provider)
 124                 {
 125                         if (targetType == typeof (string))
 126                                 return String.Empty;
 127                         if (targetType == typeof (DBNull))
 128                                 return this;
 129                         throw new InvalidCastException ();
 130                 }
 131
 132                 ushort IConvertible.ToUInt16 (IFormatProvider provider)
 133                 {
 134                         throw new InvalidCastException ();
 135                 }
 136
 137                 uint IConvertible.ToUInt32 (IFormatProvider provider)
 138                 {
 139                         throw new InvalidCastException ();
 140                 }
 141
 142                 ulong IConvertible.ToUInt64 (IFormatProvider provider)
 143                 {
 144                         throw new InvalidCastException ();
 145                 }
 146
 147                 public override string ToString ()
 148                 {
 149                         return String.Empty;
 150                 }
 151
 152                 public string ToString (IFormatProvider provider)
 153                 {
 154                         return String.Empty;
 155                 }
 156         }
 157 }