".NET的堆和棧"系列：

在" ASP.NET堆和棧一之基本概念和值類型內存分配"中，了解了"堆"和"棧"的基本概念，以及值類型的內存分配。我們知道：當執行一個方法的時候，值類型實例會在"棧"上分配內存，而引用類型實例會在"堆"上分配內存，當方法執行完畢，"棧"上的實例由操作系統自動釋放，"堆"上的實例由.NET Framework的GC進行回收。

在" ASP.NET堆和棧二之值類型和引用類型參數傳遞和內存分配"中，我們了解了值類型參數和引用類型參數在傳遞時的內存分配情況。

而本篇的重點要放在：引用類型對象拷貝以及內存分配。

引用類型對象拷貝 成員都是值類型

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());    }

輸出結果：
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，當引用類型的屬性、成員都是值類型的時候，拷貝是完全拷貝。

引用類型對象拷貝 包含引用類型成員

把Shoe由struct值類型改成引用類型class。

public class Shoe{    public string Color;}

再次運行，輸出結果：
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

當Dude類包含引用類型屬性Shoe的時候，在托管堆上的情況是這樣的：

拷貝后，2個Dude的Shoe類型的屬性指向了同一個托管堆內的Shoe實例，改變Shoe的值會同時影響到2個Dude。

很顯然，這不是我們期望的完全拷貝，如何做到完全拷貝呢？
--實現ICloneable接口

ICloneable接口的Clone()方法，允許我們在拷貝的時候，進行一些自定義設置。

讓引用類Shoe實現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類型屬性Color之所以可以使用Color.Clone()方法，是因為string也實現了ICloneable接口；又由于Clone()返回類型是object，所以，在使用Color.Clone()方法之后，需要把object轉換成string類型。

現在，在Dude類的CopyDude()方法中，當拷貝Shoe類型屬性的時候，就可以使用Shoe獨有的拷貝方法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;}

客戶端程序：

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());    }

輸出結果：
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

這正是我們期望的完全拷貝！

完全拷貝，托管堆上的情況是這樣的：

當然也可以讓同時包含值類型和引用類型成員，同時需要拷貝的類實現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}

客戶端調用：

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());     }

輸出結果：
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.

也是我們期望的完全拷貝！

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