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("IsLongReference");
  57                         //TODO: How to load the exact type?
  58                         //Does that matter? No idea :(
  59                         Object target = info.GetValue("TargetObject",typeof(System.Object));
  60
  61                         AllocateHandle(target);
  62                 }
  63
  64
  65                 // Properties
  66                 public virtual bool IsAlive
  67                 {
  68                         get
  69                         {
  70                                 //Target property takes care of the exception
  71                                 return (Target != null);
  72                         }
  73                 }
  74
  75                 public virtual object Target
  76                 {
  77                         get
  78                         {
  79                                 //Exception is thrown by gcHandle's Target
  80                                 return this.gcHandle.Target;
  81                         }
  82                         set
  83                         {
  84                                 this.gcHandle.Target = value;
  85                         }
  86                 }
  87
  88                 public virtual bool TrackResurrection
  89                 {
  90                         get
  91                         {
  92                                 return this.isLongReference;
  93                         }
  94                 }
  95
  96                 //Methods
  97                 ~WeakReference()
  98                 {
  99                         gcHandle.Free();
 100                 }
 101
 102                 //TODO
 103                 public virtual void GetObjectData(SerializationInfo info,StreamingContext context)
 104                 {
 105                         if (info == null)
 106                                 throw new ArgumentNullException ("info");
 107
 108                         info.AddValue("IsLongReference",this.isLongReference);
 109                         try
 110                         {
 111                                 info.AddValue("TargetObject",Target);
 112                         }
 113                         catch(Exception)
 114                         {
 115                                 info.AddValue("TargetObject",null);
 116                         }
 117                 }
 118         }
 119 }