泛型弱引用（不继承 System.WeakReference）

代码

public   class  WeakReference < T >  : IDisposable
    {
         private  GCHandle handle;
         private   bool  trackResurrection;

         public  WeakReference(T target) :  this (target,  false ) { }

         public  WeakReference(T target,  bool  trackResurrection)
        {
             this .trackResurrection  =  trackResurrection;
             this .Target  =  target;
        }

         ~ WeakReference()
        {
            Dispose();
        }

         public   void  Dispose()
        {
            handle.Free();
            GC.SuppressFinalize( this );
        }

         public   virtual   bool  IsAlive
        {
             get  {  return  (handle.Target  !=   null ); }
        }

         public   virtual   bool  TrackResurrection
        {
             get  {  return   this .trackResurrection; }
        }

         public   virtual  T Target
        {
             get
            {
                 object  o  =  handle.Target;
                 if  ((o  ==   null )  ||  ( ! (o  is  T)))
                     return   default (T);
                 else
                     return  (T)o;
            }
             set
            {
                handle  =  GCHandle.Alloc(value,  this .trackResurrection  ?  GCHandleType.WeakTrackResurrection : GCHandleType.Weak);
            }
        }
    }