[.NET] 子对象方法的参数，参考子对象型别做为输入型别

在设计父对象的时候，会遇到对象方法的参数为类别本身，然后再由子对象去实做这个方法的场合，例如：比较对象是否相等的方法。在这个情景中，通常会设计为下列范例的写法，在子对象中先做转型、再做比较。

 

这是一种可以正常运作的设计，但是子对象的方法参数会是父对象型别，而不是子对象型别。

 

 

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namespace ConsoleApplication1 {     class Program     {         static void Main(string[] args)         {             ChildAddress addressA = new ChildAddress();             addressA.Value001 = "123";               ChildAddress addressB = new ChildAddress();             addressB.Value001 = "123";               Console.WriteLine(addressA.EqualAddress(addressB));             Console.ReadLine();         }     } }   namespace ConsoleApplication1 {     public abstract class Address     {         // Methods              public abstract bool EqualAddress(Address address);     }       public class ChildAddress : Address     {         // Properties                                           public string Value001 { get; set; }             // Methods            public override bool EqualAddress(Address address)         {             // Require             ChildAddress childAddress = address as ChildAddress;             if (childAddress == null) return false;               // Equal             if (childAddress.Value001 == this.Value001)             {                 return true;             }             else             {                 return false;             }         }     } }

在一些情景中，如果希望子对象方法的参数，是参考子对象型别来做为输入型别，依照下列的泛型写法就可以完成这个目标。

 

 

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namespace ConsoleApplication2 {     class Program     {         static void Main(string[] args)         {             ChildAddress addressA = new ChildAddress();             addressA.Value001 = "123";               ChildAddress addressB = new ChildAddress();             addressB.Value001 = "123";               Console.WriteLine(addressA.EqualAddress(addressB));             Console.ReadLine();         }     } }   namespace ConsoleApplication2 {     public abstract class Address<TAddress>         where TAddress : Address<TAddress>     {         // Methods              public abstract bool EqualAddress(TAddress address);     }       public class ChildAddress : Address<ChildAddress>     {         // Properties                                           public string Value001 { get; set; }             // Methods            public override bool EqualAddress(ChildAddress address)         {             // Equal             if (address.Value001 == this.Value001)             {                 return true;             }             else             {                 return false;             }         }     } }

上列这两种范例，主要是应用的情景有些许不同。
第一个范例较常用在：子对象做为注入框架的对象。
第二个范例较常用在：子对象提供给外部系统使用时。