C#中的弱引用

用代码说明：

    class Program
    {
        static void Main(string[] args)
        {
            DoWork();
            Console.WriteLine(P.Target == null);
            GC.Collect();
            Console.WriteLine(P.Target == null);

            Console.ReadLine();
        }

        public static WeakReference P;
        public static void DoWork()
        {
            var p = GetPerson();
            P = new WeakReference(p);
        }

        public static Person GetPerson()
        {
            return new Person();
        }
    }
    public class Person : IDisposable
    {
     
        public Person()
        {
        
            for (int i = 0; i < new Random().Next(18, 80); i++)
            {
                this.Memo.Append((char)new Random().Next(97, 123));
            }
        }


        public StringBuilder Memo { get; set; }


        public bool IsDisposed { get; set; }
        #region IDisposable 成员

        public void Dispose()
        {
            if (!this.IsDisposed)
            {
                Console.WriteLine("Person Dispose...");

                this.Memo.Remove(0, this.Memo.Length);
                this.IsDisposed = true;
                GC.SuppressFinalize(this);
            }
        }

        #endregion

        ~Person()
        {
            Console.WriteLine("Person Unctor...");
            this.Dispose();
        }
    }