原型模式

1.回顾单例模式(Singleton Pattern)

　　设置一个静态的构造函数，让Student仅能被new一个，给所有调用返回一个相同的实例

　　StudentPrototype类代码如下：

using System;
using System.Threading;
namespace Prototype
{
    class StudentPrototype
    {
        public String Name="kxy";
        private StudentPrototype()
        {
            Thread.Sleep(2000);
            Console.WriteLine("执行StudentPrototype构造函数");
        }
        private static StudentPrototype _studentPrototype=null;
        static StudentPrototype()
        {
            _studentPrototype = new StudentPrototype();
        }
        public static StudentPrototype GetStudent()
        {
            return _studentPrototype;
        }
    }
}

　　Program代码如下：

using System;

namespace Prototype
{
    class Program
    {
        static void Main(string[] args)
        {
            StudentPrototype studentPrototype1 = StudentPrototype.GetStudent();
            studentPrototype1.Name = "flt";//赋新值之前，Name的值为kxy
            StudentPrototype studentPrototype2 = StudentPrototype.GetStudent();
            studentPrototype2.Name = "wzz";
            StudentPrototype studentPrototype3 = StudentPrototype.GetStudent();
            StudentPrototype studentPrototype4 = StudentPrototype.GetStudent();
            Console.Read();
        }
    }
}

　　因为studentPrototype1和studentPrototype2是调用了同个实例，所以

　　当执行studentPrototype2.Name = "wzz"时，studentPrototype1的Name属性也会变成wzz

　　同理，studentPrototype3、studentPrototype4也是使用这个实例

2.原型模式（Prototype Pattern）

　　原型模式是对一个原型的Clone，并返回一个新的实例

　　可理解为，在单例的基础上，Clone这个单例，并返回Clone出来的新实例，这个单例就是原型

　　StudentPrototype类代码如下：

using System;
using System.Threading;
namespace Prototype
{
    class StudentPrototype
    {
        public String Name="kxy";
        private StudentPrototype()
        {
            Thread.Sleep(2000);
            Console.WriteLine("执行StudentPrototype构造函数");
        }
        private static StudentPrototype _studentPrototype=null;
        static StudentPrototype()
        {
            _studentPrototype = new StudentPrototype();
        }
        public static StudentPrototype GetStudent()
        {
            return (StudentPrototype)_studentPrototype.MemberwiseClone();//返回一个Clone的例子
        }
    }
}

　　这时候因为studentPrototype1和studentPrototype2不是使用同一个实例，所以

　　当执行studentPrototype2.Name = "wzz"时，studentPrototype1的Name并不会受到影响，依旧是flt

　　同理，studentPrototype3、studentPrototype4也是使用了Clone出来的新实例

3.Clone的缺陷

　　MemberwiseClone是一种浅克隆，无法克隆引用参数

　　如，在StudentPrototype类中引入StuScore

using System;
using System.Threading;
namespace Prototype
{
    class StudentPrototype
    {
        public String Name = "kxy";
        private static StudentPrototype _studentPrototype = null;
        public StuScore stuScore;
        private StudentPrototype()
        {
            Thread.Sleep(2000);
            Console.WriteLine("执行StudentPrototype构造函数");
        }
        static StudentPrototype()
        {
            _studentPrototype = new StudentPrototype();
            _studentPrototype.stuScore = new StuScore();//实例化_studentPrototype这个实力中StuScore的实例，外面函数才能赋值
        }
        public static StudentPrototype GetStudent()
        {
            return (StudentPrototype)_studentPrototype.MemberwiseClone();
        }
    }
    class StuScore
    {
        public int Number = 0;
        public double Score = 0;
    }
}

　　Program

using System;

namespace Prototype
{
    class Program
    {
        static void Main(string[] args)
        {
            StudentPrototype studentPrototype1 = StudentPrototype.GetStudent();
            studentPrototype1.Name = "flt";
            studentPrototype1.stuScore.Number = 108;
            studentPrototype1.stuScore.Score = 95;
            StudentPrototype studentPrototype2 = StudentPrototype.GetStudent();
            studentPrototype2.Name = "wzz";
            studentPrototype2.stuScore.Number = 124;
            studentPrototype2.stuScore.Score = 85;

            StudentPrototype studentPrototype3 = StudentPrototype.GetStudent();
            StudentPrototype studentPrototype4 = StudentPrototype.GetStudent();
            Console.Read();
        }
    }
}

　　这时候因为studentPrototype1和studentPrototype2不是使用同一个实例，所以

　　当执行studentPrototype2.Name = "wzz"时，studentPrototype1的Name并不会受到影响，依旧是flt

　　这个和上述一样

　　但是当执行

　　　　studentPrototype2.stuScore.Number = 124;

　　　　studentPrototype2.stuScore.Score = 85;

　　时，studentPrototype1的stuScore的属性值会被改变

　　因为浅克隆并不会克隆出一个新的StuScore的实例，而是所有克隆出来的StudentPrototype实力都引用同一个StuScore实例

　　即引用类型的对象并不会被Clone出一个新的实例

4.浅克隆缺陷的解决方法

　　借助序列化、反序列化实现深度Clone

 　　新建一个类SerializeHelper，用来对对象进行序列化和反序列化

　　代码如下：

using System;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;

namespace Prototype
{
    public class SerializeHelper
    {
        public static string Serializable(object target)//序列化，把对象序列化为一个字符串
        {
            using (MemoryStream stream = new MemoryStream())
            {
                new BinaryFormatter().Serialize(stream, target);
                return Convert.ToBase64String(stream.ToArray());
            }
        }
        public static T Derializable<T>(string target)//反序列化，把字符串反序列化成一个对象
        {
            byte[] targetArray = Convert.FromBase64String(target);
            using (MemoryStream stream = new MemoryStream(targetArray))
            {
                return (T)(new BinaryFormatter().Deserialize(stream));
            }
        }
        public static T DeepClone<T>(T t)//用序列化和反序列化实现深克隆
        {
            return Derializable<T>(Serializable(t));
        }
    }
}

　　在对对象进行序列化时，对象所对应的类要有一个序列化的特性，即在类名上面加上[Serializable]

　　

　　Program代码如下：

using System;

namespace Prototype
{
    class Program
    {
        static void Main(string[] args)
        {
            StudentPrototype studentPrototype1 = StudentPrototype.GetStudent();
            studentPrototype1.Name = "flt";
            studentPrototype1.stuScore.Number = 108;
            studentPrototype1.stuScore.Score = 95;

            StudentPrototype studentPrototype2 = StudentPrototype.GetStudent();
            studentPrototype2.Name = "wzz";
            studentPrototype2.stuScore.Number = 124;
            studentPrototype2.stuScore.Score = 85;

            StudentPrototype studentPrototype3 = SerializeHelper.DeepClone(StudentPrototype.GetStudent());
            studentPrototype3.Name = "zjx";
            studentPrototype3.stuScore.Number = 223;
            studentPrototype3.stuScore.Score = 90;


            StudentPrototype studentPrototype4 = StudentPrototype.GetStudent();
            Console.Read();
        }
    }
}

　　studentPrototype3 是深度克隆的对象，连stuScore也是一个新的Clone实例，所以执行

　　　　studentPrototype3.stuScore.Number = 223；

　　　　studentPrototype3.stuScore.Score = 90;

　　并不会影响到studentPrototype1和studentPrototype2的stuScore