".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。
202281395823811.png
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：
202281395823812.png
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：
202281395823813.png
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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发表于 2023-5-4 11:32:42