mcs/class/corlib/System/WeakReference.cs

   1 //
   2 // System.WeakReference.cs
   3 //
   4 // Author:
   5 //   Ajay kumar Dwivedi (adwiv@yahoo.com)
   6 //
   7
   8 using System.Runtime.Serialization;
   9 using System.Runtime.InteropServices;
  10
  11 namespace System
  12 {
  13         /// <summary>
  14         /// Summary description for WeakReference.
  15         /// </summary>
  16         [Serializable]
  17         public class WeakReference : ISerializable
  18         {
  19                 //Fields
  20                 private bool isLongReference;
  21                 private GCHandle gcHandle;
  22
  23                 // Helper method for constructors
  24                 //Should not be called from any other method.
  25                 private void AllocateHandle(Object target)
  26                 {
  27                         if(this.isLongReference)
  28                         {
  29                                 this.gcHandle = GCHandle.Alloc(target, GCHandleType.WeakTrackResurrection);
  30                         }
  31                         else
  32                         {
  33                                 this.gcHandle = GCHandle.Alloc(target, GCHandleType.Weak);
  34                         }
  35                 }
  36
  37
  38                 //Constructors
  39                 public WeakReference(object target)
  40                         : this(target,false)
  41                 {}
  42
  43
  44                 public WeakReference(object target, bool trackResurrection)
  45                 {
  46                         this.isLongReference = trackResurrection;
  47                         AllocateHandle(target);
  48                 }
  49
  50
  51                 protected WeakReference(SerializationInfo info, StreamingContext context)
  52                 {
  53                         if (info == null)
  54                                 throw new ArgumentNullException ("info");
  55
  56                         this.isLongReference = info.GetBoolean ("TrackResurrection");
  57                         Object target = info.GetValue ("TrackedObject", typeof (System.Object));
  58
  59                         AllocateHandle(target);
  60                 }
  61
  62
  63                 // Properties
  64                 public virtual bool IsAlive
  65                 {
  66                         get
  67                         {
  68                                 //Target property takes care of the exception
  69                                 return (Target != null);
  70                         }
  71                 }
  72
  73                 public virtual object Target
  74                 {
  75                         get
  76                         {
  77                                 //Exception is thrown by gcHandle's Target
  78                                 return this.gcHandle.Target;
  79                         }
  80                         set
  81                         {
  82                                 this.gcHandle.Target = value;
  83                         }
  84                 }
  85
  86                 public virtual bool TrackResurrection
  87                 {
  88                         get
  89                         {
  90                                 return this.isLongReference;
  91                         }
  92                 }
  93
  94                 //Methods
  95                 ~WeakReference()
  96                 {
  97                         gcHandle.Free();
  98                 }
  99
 100                 public virtual void GetObjectData(SerializationInfo info, StreamingContext context)
 101                 {
 102                         if (info == null)
 103                                 throw new ArgumentNullException ("info");
 104
 105                         info.AddValue ("TrackResurrection", TrackResurrection);
 106
 107                         try {
 108                                 info.AddValue ("TrackedObject", Target);
 109                         } catch(Exception) {
 110                                 info.AddValue("TrackedObject",null);
 111                         }
 112                 }
 113         }
 114 }