C# 浅拷贝和深拷贝的实现

拷贝（复制）为对象创建副本，即将对象中的所有字段复制到新的对象（副本中）。拷贝有两种：浅拷贝和深拷贝，微软建议用类型继承ICloneable接口的方式明确该类型是可以被拷贝的，ICloneable接口只提供了一个Clone方法，需要根据需要在Clone方法内实现浅拷贝或深拷贝。

1、浅拷贝：把源对象中的值类型字段的值和引用类型字段的引用复制到副本中。在源对象（副本）中，修改值类型字段的值不会影响到副本（源对象），而修改引用类型字段的值会影响到副本（源对象）。

注意：string类型除外，虽然string类型是引用类型，但是由于该引用类型的特殊性，在浅拷贝过程，副本中会创建新的字符串并把对应的值复制过来，字符串应被看成值类型。

浅拷贝声明代码，使用Object.MeberwiseClone方法进行浅拷贝：

    class Employee : ICloneable
    {
        public string ID { get; set; }
        public int Age { get; set; }
        public Department DepartmentName { get; set; }

        //实现ICloneable接口的Clone方法
        public object Clone()
        {
            return this.MemberwiseClone();//浅拷贝
        }
    }
    class Department
    {
        public string DepartmentName { get; set; }
        public Department(string value)
        {
            DepartmentName = value;
        }
        public override string ToString()
        {
            return DepartmentName.ToString();
        }
    }

调用浅拷贝代码：

     Employee emp1 = new Employee()
     {
         ID = "NO1",
         Age = 20,
         DepartmentName = new Department("Technology")
     };
     Employee emp2 = emp1.Clone() as Employee;//浅拷贝

     Console.WriteLine("-------初始化赋值------");
     Console.WriteLine(string.Format("[emp1] id:{0}	age:{1}	department:{2}", emp1.ID, emp1.Age, emp1.DepartmentName));
     Console.WriteLine(string.Format("[emp2] id:{0}	age:{1}	department:{2}", emp2.ID, emp2.Age, emp2.DepartmentName));

     Console.WriteLine("
-------改变emp1的值-------");
     emp1.ID = "NO2";
     emp1.Age = 22;
     emp1.DepartmentName.DepartmentName = "sales";
     Console.WriteLine(string.Format("[emp1] id:{0}	age:{1}	department:{2}", emp1.ID, emp1.Age, emp1.DepartmentName));
     Console.WriteLine(string.Format("[emp2] id:{0}	age:{1}	department:{2}", emp2.ID, emp2.Age, emp2.DepartmentName));

     Console.WriteLine("
-------改变emp2的值-------");
     emp2.ID = "NO3";
     emp2.Age = 24;
     emp2.DepartmentName.DepartmentName = "personnel";
     Console.WriteLine(string.Format("[emp1] id:{0}	age:{1}	department:{2}", emp1.ID, emp1.Age, emp1.DepartmentName));
     Console.WriteLine(string.Format("[emp2] id:{0}	age:{1}	department:{2}", emp2.ID, emp2.Age, emp2.DepartmentName));

运行结果：

-------初始化赋值------
[emp1] id:NO1   age:20  department:Technology
[emp2] id:NO1   age:20  department:Technology

-------改变emp1的值-------
[emp1] id:NO2   age:22  department:sales
[emp2] id:NO1   age:20  department:sales

-------改变emp2的值-------
[emp1] id:NO2   age:22  department:personnel
[emp2] id:NO3   age:24  department:personnel

从结果可以看出，Age是值类型，ID是string类型这里被当做值类型处理，所以ID和Age修改了对另一个对象没有影响；Department属性是引用类型，浅拷贝emp1和emp2引用的是同一个Department对象，其中一个修改了DepartmentName的值会影响另一个。

2、深拷贝：把源对象的值类型字段和引用类型字段，重新创建并赋值。在源对象（副本）中，修改值类型字段的值或者引用类型字段的值都不会影响到副本（源对象）。

建议使用序列化的形式来进行深拷贝

深拷贝代码：

    [Serializable]//标记可序列化
    class Employee : ICloneable
    {
        public string ID { get; set; }
        public int Age { get; set; }
        public Department DepartmentName { get; set; }

        //实现ICloneable接口的Clone方法
        public object Clone()
        {
            using (MemoryStream stream = new MemoryStream())
            {
                BinaryFormatter formatter = new BinaryFormatter();
                formatter.Serialize(stream, this);
                stream.Seek(0, SeekOrigin.Begin);
                return formatter.Deserialize(stream) as Employee;
            }
        }
    }

    [Serializable]//标记可序列化
    class Department
    {
        public string DepartmentName { get; set; }
        public Department(string value)
        {
            DepartmentName = value;
        }
        public override string ToString()
        {
            return DepartmentName.ToString();
        }
    }

跟上面调用浅拷贝代码一样调用深拷贝，运行结果：

-------初始化赋值------
[emp1] id:NO1   age:20  department:Technology
[emp2] id:NO1   age:20  department:Technology

-------改变emp1的值-------
[emp1] id:NO2   age:22  department:sales
[emp2] id:NO1   age:20  department:Technology

-------改变emp2的值-------
[emp1] id:NO2   age:22  department:sales
[emp2] id:NO3   age:24  department:personnel

拷贝以后，无论是修改值类型还是引用类型，都对另一个对象没有影响。

3、要同时实现深拷贝和浅拷贝，可以在Clone方法外，额外实现两个方法，声明为DeepClone和Shallow：

    [Serializable]//标记可序列化
    class Employee : ICloneable
    {
        public string ID { get; set; }
        public int Age { get; set; }
        public Department DepartmentName { get; set; }

        //实现ICloneable接口的Clone方法
        public object Clone()
        {
            return this.MemberwiseClone();
        }

        //深拷贝
        public Employee DeepClone()
        {
            using (MemoryStream stream = new MemoryStream())
            {
                BinaryFormatter formatter = new BinaryFormatter();
                formatter.Serialize(stream, this);
                stream.Seek(0, SeekOrigin.Begin);
                return formatter.Deserialize(stream) as Employee;
            }
        }

        //浅拷贝
        public Employee Shallow()
        {
            return this.Clone() as Employee;
        }
    }

参考：《编写高质量代码改善C#程序的157个建议》陆敏技