準備技術：

?????1.C#基礎知識

?????2.了解WCF基礎知識

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?????在正常的c#開發中我們是允許用子類去替換基類的，這也是所謂的替換原則。但是我們在WCF中確不能用數據契約的子類來替換父類的，因為這中間存在一個序列化的問題。舉個例子：

?????我們有數據契約：

??????????[DataContract]

??????????class Employee{...}

?????服務契約中：

??????????[ServiceContract]

??????????interface IEmployeeManager

??????????{

???????????????[OperationContract]

???????????????void AddEmployee(Employee employee);

??????????}

?????然后我們在客戶端的代理中就算有類：Intern繼承于

??????????[DataContract]

??????????class Intern:Employee{...}

?????然后再客戶端調用時：

??????????proxy.AddEmployee(new Intern())是會出錯的。因為在服務器端無法識別Intern對象，因為他無法去反序列化Intern成Employee對象(WCF序列化)。

?????

?????

?????WCF提供給我們了一個解決的辦法就是使用KnownTypeAttribute特性，在基類上標識對應的子類就可以了。KnownTypeAttribute特性可以使用在Struct跟Class上。示例：

??????????[DataContract]

??????????[KnownType(typeof(Customer))]

??????????class Employee{...}

??????????

??????????[DataContract]

??????????class Intern:Employee{...}

這樣我們就在所有的契約跟操作上，能跨越所有的服務和終結點，允許服務接受子類。但是這樣會遇到一個問題，我們不能去特定的指定某一個服務操作，所以KnownType的缺陷就是范圍過于廣泛。WCF提供了另外一個Attribute--ServiceKnownType.

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ServiceKnownType 特性

?????KnownType只能應用在數據契約的基類上，而ServiceKnownType可以在Interface、Method、Class上標識。看一個示例Employee.cs：

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Code
using?System;
using?System.Collections.Generic;
using?System.Linq;
using?System.Text;
using?System.ServiceModel;
using?System.Runtime.Serialization;

namespace?HenllyeeDataContract
{
????[DataContract]
????public?class?Employee
????{
????????#region?Fields
????????private?string?_name;
????????private?int?_age;
????????#endregion

????????#region?Properties
????????///?<summary>
????????///?The?employee's?name
????????///?</summary>
????????[DataMember(Order=0)]
????????public?string?Name
????????{
????????????get?
????????????{
????????????????return?this._name;
????????????}
????????????set
????????????{
????????????????this._name?=?value;
????????????}
????????}

????????///?<summary>
????????///?The?employee's?age
????????///?</summary>
????????[DataMember(Order=1)]
????????public?int?Age
????????{
????????????get
????????????{
????????????????return?this._age;
????????????}
????????????set
????????????{
????????????????this._age?=?value;
????????????}
????????}
????????#endregion
????}

????[DataContract]
????public?class?Intern?:?Employee
????{
????????private?int?_internship;

????????///?<summary>
????????///?The?intern's?working?days
????????///?</summary>
????????[DataMember]
????????public?int?Internship
????????{
????????????get
????????????{
????????????????return?this._internship;
????????????}
????????????set
????????????{
????????????????this._internship?=?value;
????????????}
????????}
????}
}

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在數據契約中我們并沒有去指定KnownType，我們在服務契約的操作上去標識ServiceKnownType特性，EmployeeManage.cs:

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Code
using?System;
using?System.Collections.Generic;
using?System.Linq;
using?System.Text;
using?System.ServiceModel;
using?System.Runtime.Serialization;

namespace?HenllyeeServiceContract
{
????[ServiceContract]
????public?interface?IEmployeeManage
????{
????????[OperationContract]
????????[ServiceKnownType(typeof(HenllyeeDataContract.Intern))]
????????void?AddEmployee(HenllyeeDataContract.Employee?emlpoyee);

????????[OperationContract]
????????[ServiceKnownType(typeof(HenllyeeDataContract.Intern))]
????????HenllyeeDataContract.Employee?GetEmployee();
????}

????[ServiceBehavior(InstanceContextMode=InstanceContextMode.Single)]
????public?class?EmployeeManage?:?IEmployeeManage
????{
????????private?HenllyeeDataContract.Employee?_employee;

????????///?<summary>
????????///?Set?employee
????????///?</summary>
????????///?<param?name="emlpoyee">the?employee's?object</param>
????????public?void?AddEmployee(HenllyeeDataContract.Employee?emlpoyee)
????????{
????????????this._employee?=?emlpoyee;
????????}

????????///?<summary>
????????///?Get?a?employee
????????///?</summary>
????????///?<returns></returns>
????????public?HenllyeeDataContract.Employee?GetEmployee()
????????{
????????????return?this._employee;
????????}
????}
}

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在客戶端我們調用：

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Code
using?System;
using?System.Collections.Generic;
using?System.Linq;
using?System.Text;

namespace?Client
{
????class?Program
????{
????????static?void?Main(string[]?args)
????????{
????????????EmployeeService.EmployeeManageClient?proxy?=?new?Client.EmployeeService.EmployeeManageClient();
????????????EmployeeService.Intern?intern?=?new?Client.EmployeeService.Intern();
????????????intern.Age?=?22;
????????????intern.Name?=?"Henllyee?Cui";
????????????intern.Internship?=?120;
????????????proxy.AddEmployee(intern);

????????????EmployeeService.Employee?internOut?=?proxy.GetEmployee();
????????????Console.Write("The?Employee?Name:{0}\nAge:{1}\n",
????????????????internOut.Name,
????????????????internOut.Age
????????????????);
????????????Console.Read();
????????}
????}
}

運行后：?

?????ServiceKnownType特性也可以表示在數據契約的類上，那么就會應用到整個數據契約中操作上，如：

??????????[ServiceContract]

??????????[ServiceDataContract(typeof(HenllyeeDataContract.Intern))]

??????????public?interface?IEmployeeManage{...}

?????那么IEmployeeManage服務契約跟其所有的操作都可以接受Intern這個子類.

已知類型與接口

?????數據契約DataContract只能標識在class 或者struct上，但是數據契約的基類可以是接口,但是我們在服務契約的時候要去用ServiceKnownType特性去指定確切的數據類型。如:

?????interface IEmployee{...}

?????[DataContract]

?????class Intern:IEmployee{...}

服務契約中：

?????[ServiceContract]

?????[ServiceKnownType(typeof(Intern))]

?????interface IEmployeeManage

?????{

??????????[OperationContract]

??????????void AdddEmployee(IEmployee employee);

?????}

要注意的一點就是我們不能把KnownType特性應用到基接口上，因為客服端導出的元數據是不能包含接口本身的。

[代碼下載]

作者：Henllyee Cui
出處： http://henllyee.cnblogs.com/
本文版權歸作者和博客園共有，歡迎轉載，但未經作者同意必須保留此段聲明。

轉載于:https://www.cnblogs.com/Henllyee/archive/2008/08/26/1276995.html

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