.NET面试基础知识之序列化(Serialize)(三)

Serializing a Type as a different type and deserializing an object as a different object

下面的代码是序列化一个Singleton类并反序列化

　　[Serializable]
    public sealed class SingletonSerializable:ISerializable
    {
        private SingletonSerializable()
        {
        }

        private static readonly SingletonSerializable theOneObject=new SingletonSerializable();

        public string Name="Jeff";
        public DateTime Date = DateTime.Now;

        public static SingletonSerializable GetSingleton()
        {
            return theOneObject;
        }

        [SecurityPermission(SecurityAction.Demand, SerializationFormatter = true)]
        void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
        {
            info.SetType(typeof(SingletonSerializationHelper));

　　　　　　　//Tell the formatter to serialize the SingletonSerializable object as a SingletonSerializableHelper object instead.

　　　　　　//The formatter automatically detected that both array elements refer to a single object, the formatter serialize only one object.

　　　　　　//So the formatter no need the special constructor
        }

        [Serializable]

　　　　 //When a type implements IObjectReference, the formatter calls the GetRealObject method
        private sealed class SingletonSerializationHelper:IObjectReference
        {
            public Object GetRealObject(StreamingContext context)
            {
                return SingletonSerializable.GetSingleton();

　　　　　　　　　　//Return a reference to the object that you really want a reference to now that deserialization of the object has completed.
            }
        }
    }

test

　　public static void TestSingleton()
    {
        SingletonSerializable[] al = { SingletonSerializable.GetSingleton(),SingletonSerializable.GetSingleton()};
        Console.WriteLine("Do both elements refer to the same object?"+(al[0]==al[1]));//True

        using (Stream st = new MemoryStream()) {
        　　 BinaryFormatter formatter = new BinaryFormatter();
            formatter.Serialize(st,al);
            st.Position = 0;
            SingletonSerializable[] a2 =(SingletonSerializable[]) formatter.Deserialize(st);
            Console.WriteLine("Do both elements refer to the same object?"+(a2[0]==a2[1]));//True
            Console.WriteLine("Do both elements refer to the same object?"+(al[0]==a2[0]));//True
        }
    }