ASP.NET堆和栈三之引用类型对象拷贝和内存分配

Petunia ·

更新时间:2024-09-20

· 661 次阅读

".NET的堆和栈"系列：

ASP.NET堆和栈一之基本概念和值类型内存分配

ASP.NET堆和栈二之值类型和引用类型参数传递和内存分配

ASP.NET堆和栈三之引用类型对象拷贝和内存分配

ASP.NET堆和栈四之对托管和非托管资源垃圾的回收和内存分配

在" ASP.NET堆和栈一之基本概念和值类型内存分配"中，了解了"堆"和"栈"的基本概念，以及值类型的内存分配。我们知道：当执行一个方法的时候，值类型实例会在"栈"上分配内存，而引用类型实例会在"堆"上分配内存，当方法执行完毕，"栈"上的实例由操作系统自动释放，"堆"上的实例由.NET Framework的GC进行回收。

在" ASP.NET堆和栈二之值类型和引用类型参数传递和内存分配"中，我们了解了值类型参数和引用类型参数在传递时的内存分配情况。

而本篇的重点要放在：引用类型对象拷贝以及内存分配。

引用类型对象拷贝成员都是值类型

public struct Shoe
{
    public string Color;
}
public class Dude
{
    public string Name;
    public Shoe RightShoe;
    public Shoe LeftShoe;
    public Dude CopyDude()
    {
        Dude newPerson = new Dude();
        newPerson.Name = Name;
        newPerson.LeftShoe = LeftShoe;
        newPerson.RightShoe = RightShoe;
        return newPerson;
    }
    public override string ToString()
    {
        return (Name + " : Dude!, I have a " + RightShoe.Color  +
        " shoe on my right foot, and a " +
        LeftShoe.Color + " on my left foot.");
    }
}
public static void Main()
{
    Dude Bill = new Dude();
    Bill.Name = "Bill";
    Bill.LeftShoe = new Shoe();
    Bill.RightShoe = new Shoe();
    Bill.LeftShoe.Color = Bill.RightShoe.Color = "Blue";
    Dude Ted =  Bill.CopyDude();
    Ted.Name = "Ted";
    Ted.LeftShoe.Color = Ted.RightShoe.Color = "Red";
    Console.WriteLine(Bill.ToString());
    Console.WriteLine(Ted.ToString());            
}

输出结果：
Bill : Dude!, I have a Red shoe on my right foot, and a Red on my left foot
Ted : Dude!, I have a Red shoe on my right foot, and a Red on my left foot

以上，当引用类型的属性、成员都是值类型的时候，拷贝是完全拷贝。

引用类型对象拷贝包含引用类型成员

把Shoe由struct值类型改成引用类型class。

public class Shoe
{
    public string Color;
}

再次运行，输出结果：
Bill : Dude!, I have a Red shoe on my right foot, and a Red on my left foot
Ted : Dude!, I have a Red shoe on my right foot, and a Red on my left foot

当Dude类包含引用类型属性Shoe的时候，在托管堆上的情况是这样的：

拷贝后，2个Dude的Shoe类型的属性指向了同一个托管堆内的Shoe实例，改变Shoe的值会同时影响到2个Dude。

很显然，这不是我们期望的完全拷贝，如何做到完全拷贝呢？
--实现ICloneable接口

ICloneable接口的Clone()方法，允许我们在拷贝的时候，进行一些自定义设置。

让引用类Shoe实现ICloneable接口。

public class Shoe : ICloneable
{
    public string Color;
    public object Clone()
    {
        Shoe newShoe = new Shoe();
        newShoe.Color = Color.Clone() as string;
        return newShoe;
    }
}

以上，Shoe的string类型属性Color之所以可以使用Color.Clone()方法，是因为string也实现了ICloneable接口；又由于Clone()返回类型是object，所以，在使用Color.Clone()方法之后，需要把object转换成string类型。

现在，在Dude类的CopyDude()方法中，当拷贝Shoe类型属性的时候，就可以使用Shoe独有的拷贝方法Clone()。

public Dude CopyDude()
{
    Dude newPerson = new Dude();
    newPerson.Name = Name;
    newPerson.LeftShoe = LeftShoe.Clone() as Shoe;
    newPerson.RightShoe = RightShoe.Clone() as Shoe;
    return newPerson;
}

客户端程序：

public static void Main()
{
    Dude Bill = new Dude();
    Bill.Name = "Bill";
    Bill.LeftShoe = new Shoe();
    Bill.RightShoe = new Shoe();
    Bill.LeftShoe.Color = Bill.RightShoe.Color = "Blue";
    Dude Ted =  Bill.CopyDude();
    Ted.Name = "Ted";
    Ted.LeftShoe.Color = Ted.RightShoe.Color = "Red";
    Console.WriteLine(Bill.ToString());
    Console.WriteLine(Ted.ToString());            
}

输出结果：
Bill : Dude!, I have a Blue shoe on my right foot, and a Blue on my left foot
Ted : Dude!, I have a Red shoe on my right foot, and a Red on my left foot

这正是我们期望的完全拷贝！

完全拷贝，托管堆上的情况是这样的：

当然也可以让同时包含值类型和引用类型成员，同时需要拷贝的类实现ICloneable接口。

public class Dude: ICloneable
{
    public string Name;
    public Shoe RightShoe;
    public Shoe LeftShoe;
    public override string ToString()
    {
        return (Name + " : Dude!, I have a " + RightShoe.Color  +
            " shoe on my right foot, and a " +
            LeftShoe.Color + " on my left foot.");
    }
    #region ICloneable Members
    public object Clone()
    {
        Dude newPerson = new Dude();
        newPerson.Name = Name.Clone() as string;
        newPerson.LeftShoe = LeftShoe.Clone() as Shoe;
        newPerson.RightShoe = RightShoe.Clone() as Shoe;
        return newPerson;
    }
    #endregion
}

客户端调用：

public static void Main()
{
    Class1 pgm = new Class1();
    Dude Bill = new Dude();
    Bill.Name = "Bill";
    Bill.LeftShoe = new Shoe();
    Bill.RightShoe = new Shoe();
    Bill.LeftShoe.Color = Bill.RightShoe.Color = "Blue";
    Dude Ted =  Bill.Clone() as Dude;
    Ted.Name = "Ted";
    Ted.LeftShoe.Color = Ted.RightShoe.Color = "Red";
    Console.WriteLine(Bill.ToString());
    Console.WriteLine(Ted.ToString());            
}

输出结果：
Bill : Dude!, I have a Blue shoe on my right foot, and a Blue on my left foot.
Ted : Dude!, I have a Red shoe on my right foot, and a Red on my left foot.

也是我们期望的完全拷贝！

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net ASP.NET 对象引用类型拷贝 ASP

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