mcs/class/corlib/System/WeakReference.cs

   1 //
   2 // System.WeakReference.cs
   3 //
   4 // Author:
   5 //   Ajay kumar Dwivedi (adwiv@yahoo.com)
   6 //
   7
   8 //
   9 // Copyright (C) 2004 Novell, Inc (http://www.novell.com)
  10 //
  11 // Permission is hereby granted, free of charge, to any person obtaining
  12 // a copy of this software and associated documentation files (the
  13 // "Software"), to deal in the Software without restriction, including
  14 // without limitation the rights to use, copy, modify, merge, publish,
  15 // distribute, sublicense, and/or sell copies of the Software, and to
  16 // permit persons to whom the Software is furnished to do so, subject to
  17 // the following conditions:
  18 //
  19 // The above copyright notice and this permission notice shall be
  20 // included in all copies or substantial portions of the Software.
  21 //
  22 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  23 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  24 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  25 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  26 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  27 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  28 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  29 //
  30
  31 using System.Runtime.Serialization;
  32 using System.Runtime.InteropServices;
  33
  34 namespace System
  35 {
  36         [Serializable]
  37         [ComVisible (true)]
  38         public class WeakReference : ISerializable
  39         {
  40                 //Fields
  41                 private bool isLongReference;
  42                 private GCHandle gcHandle;
  43
  44                 // Helper method for constructors
  45                 //Should not be called from any other method.
  46                 private void AllocateHandle (Object target)
  47                 {
  48                         if (isLongReference) {
  49                                 gcHandle = GCHandle.Alloc (target, GCHandleType.WeakTrackResurrection);
  50                         }
  51                         else {
  52                                 gcHandle = GCHandle.Alloc (target, GCHandleType.Weak);
  53                         }
  54                 }
  55
  56                 //Constructors
  57 #if MOBILE
  58                 protected WeakReference ()
  59                 {
  60                 }
  61 #endif
  62                 public WeakReference (object target)
  63                         : this (target, false)
  64                 {
  65                 }
  66
  67                 public WeakReference (object target, bool trackResurrection)
  68                 {
  69                         isLongReference = trackResurrection;
  70                         AllocateHandle (target);
  71                 }
  72
  73                 protected WeakReference (SerializationInfo info, StreamingContext context)
  74                 {
  75                         if (info == null)
  76                                 throw new ArgumentNullException ("info");
  77
  78                         isLongReference = info.GetBoolean ("TrackResurrection");
  79                         Object target = info.GetValue ("TrackedObject", typeof (System.Object));
  80
  81                         AllocateHandle (target);
  82                 }
  83
  84                 // Properties
  85                 public virtual bool IsAlive {
  86                         get {
  87                                 //Target property takes care of the exception
  88                                 return (Target != null);
  89                         }
  90                 }
  91
  92                 public virtual object Target {
  93                         get {
  94                                 // This shouldn't throw an exception after finalization
  95                                 // http://blogs.msdn.com/b/yunjin/archive/2005/08/31/458231.aspx
  96                                 if (!gcHandle.IsAllocated)
  97                                         return null;
  98                                 return gcHandle.Target;
  99                         }
 100                         set
 101                         {
 102                                 gcHandle.Target = value;
 103                         }
 104                 }
 105
 106                 public virtual bool TrackResurrection {
 107                         get {
 108                                 return isLongReference;
 109                         }
 110                 }
 111
 112                 //Methods
 113                 ~WeakReference ()
 114                 {
 115                         gcHandle.Free ();
 116                 }
 117
 118                 public virtual void GetObjectData (SerializationInfo info, StreamingContext context)
 119                 {
 120                         if (info == null)
 121                                 throw new ArgumentNullException ("info");
 122
 123                         info.AddValue ("TrackResurrection", TrackResurrection);
 124
 125                         try {
 126                                 info.AddValue ("TrackedObject", Target);
 127                         } catch (Exception) {
 128                                 info.AddValue ("TrackedObject", null);
 129                         }
 130                 }
 131         }
 132 }