C#中的浅拷贝与深拷贝

浅拷贝

值类型的拷贝是将源拷贝对象的值赋予被拷贝对象，在修改被拷贝对象的值之后并不会影响源拷贝对象的值

public static void Main(string[] args)
{
    //值类型拷贝
    int a = 5, b = a;
    b = 6;
    Console.WriteLine($"a:{a}");
    Console.WriteLine($"b:{b}");
}

控制台输出结果:

1
2

a:5
b:6

引用类型

引用类型的拷贝只是复制源拷贝对象的引用地址给被拷贝对象，两者的引用地址都指向托管堆上的同一处对象实例，因此在修改被拷贝对象后源拷贝对象也会被修改

public static void Main(string[] args)
{
    Student A = new Student("张三", "男");
    Student B = new Student();
    B = A;
    Console.WriteLine($"A:{A.ToString()}");
    Console.WriteLine($"B:{B.ToString()}");
    B.Name = "李四";
    B.Gender = "女";
    Console.WriteLine($"A:{A.ToString()}");
    Console.WriteLine($"B:{B.ToString()}");
    Console.ReadKey();
}

public class Student
{
	public Student() { }
    public Student(string name,string gender)
    {
        this.Name = name;
        this.Gender = gender;
    }
    private string _name;
    public string Name
    {
        get { return _name; }
        set { _name = value; }
    }

    private string _gender;
    public string Gender
    {
        get { return _gender; }
        set { _gender = value; }
    }

    public override string ToString()
    {
        return $"Name:{Name},Gender:{Gender}";
    }
}

控制台输出结果:

A:Name:张三,Gender:男
B:Name:张三,Gender:男
A:Name:李四,Gender:女
B:Name:李四,Gender:女

浅拷贝亦可继承自接口ICloneable通过MemberwiseClone方法实现接口的Clone成员

public static void Main(string[] args)
{
    Student A = new Student("张三", "男");
    Student B = (Student)A.Clone();
    Console.WriteLine($"A:{A.ToString()}");
    Console.WriteLine($"B:{B.ToString()}");
    Console.ReadKey();
}

public class Student:ICloneable
{
    public Student() { }
    public Student(string name,string gender)
    {
        this.Name = name;
        this.Gender = gender;
    }
    private string _name;
    public string Name
    {
        get { return _name; }
        set { _name = value; }
    }

    private string _gender;
    public string Gender
    {
        get { return _gender; }
        set { _gender = value; }
    }

    public override string ToString()
    {
        return $"Name:{Name},Gender:{Gender}";
    }

    public object Clone()
    {
        //创建浅表副本
        return this.MemberwiseClone();
    }
}

深拷贝

通过复制对象的每个成员实现深拷贝(仍以Student为例)

public static void Main(string[] args)
{
    Student A = new Student("张三", "男");
    //Student B = new Student();
    //B.Name = A.Name;
    //B.Gender = A.Gender;
    //Console.WriteLine($"A:{A.ToString()}");
    //Console.WriteLine($"B:{B.ToString()}");
    //B.Name = "李四";
    //B.Gender = "女";
    //Console.WriteLine($"A:{A.ToString()}");
    //Console.WriteLine($"B:{B.ToString()}");

    Student B = DeepCopyByReflection<Student>(A);
    Console.WriteLine($"A:{A.ToString()}");
    Console.WriteLine($"B:{B.ToString()}");
    B.Name = "李四";
    B.Gender = "女";
    Console.WriteLine($"A:{A.ToString()}");
    Console.WriteLine($"B:{B.ToString()}");
}

/// <summary>
/// 复制对象每个成员实现深拷贝
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="obj"></param>
/// <returns></returns>
public static T DeepCopyByReflection<T>(T obj)
{
    if (obj is string || obj.GetType().IsValueType)
        return obj;
    
    object retval = Activator.CreateInstance(obj.GetType());//创建对象实例
    FieldInfo[] fields = obj.GetType().GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Instance);
    foreach (var field in fields)
    {
        try
        {
            //复制字段值
            field.SetValue(retval, DeepCopyByReflection(field.GetValue(obj)));
        }
        catch { }
    }
    return (T)retval;
}

控制台输出结果:

A:Name:张三,Gender:男
B:Name:张三,Gender:男
A:Name:张三,Gender:男
B:Name:李四,Gender:女

String 类型

到了这里产生一个疑问，String同样为引用类型，但在平时使用过程中并没有出现上述引用类型浅拷贝的问题

public static void Main(string[] args)
{
    string a = "123", b = a;
    Console.WriteLine($"a:{a}");
    Console.WriteLine($"b:{b}");

    b = "456";
    Console.WriteLine($"a:{a}");
    Console.WriteLine($"b:{b}");
    Console.ReadKey();
}