ASP.NET堆和栈三之引用类型对象拷贝和内存分配

".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。

ASP.NET堆和栈三之引用类型对象拷贝和内存分配_第1张图片

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:

ASP.NET堆和栈三之引用类型对象拷贝和内存分配_第2张图片

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:

ASP.NET堆和栈三之引用类型对象拷贝和内存分配_第3张图片

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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