.NET的堆和栈03,引用类型对象拷贝以及内存分配

11/25/2015来源:ASP.NET技巧人气:1359

在" .NET的堆和栈01,基本概念、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" .NET的堆和栈02,值类型和引用类型参数传递以及内存分配"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。

 

主要包括:
■  引用类型对象拷贝 成员都是值类型
■  引用类型对象拷贝 包含引用类型成员

 

  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。

16

 

  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:
17  

 

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:
18

 

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!

 

参考资料:
C# Heap(ing) Vs Stack(ing) in .NET: Part III

 

".NET的堆和栈"系列包括:

.NET的堆和栈01,基本概念、值类型内存分配

.NET的堆和栈02,值类型和引用类型参数传递以及内存分配

.NET的堆和栈03,引用类型对象拷贝以及内存分配

.NET的堆和栈04,对托管和非托管资源的垃圾回收以及内存分配