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重载是面向对象编程里面比较常见的一个问题，如下：

interface ICalculator
{
    int Add(int a, int b);
    double Add(double a, double b);
}

通过不同的参数列表，给出不一样的函数签名。但是在WCF通过interface公开服务契约的时候，有这样一个问题。直接在这2个Add方法上添加[OperationContract]会导致异常发生。

我们来创建一个例子，服务端代码：

interface ICalculator
{
    [OperationContract]
    int Add(int a, int b);
 
    [OperationContract]
    double Add(double a, double b);
}
 
........

static void Main(string[] args)
{
    try
    {
        ServiceHost host = new ServiceHost(typeof(Calculator));
        Binding wsHttpBinding = new WSHttpBinding();
        host.AddServiceEndpoint(typeof(ICalculator), wsHttpBinding, new Uri("http://localhost:8086/Calculator/"));
        host.Open();
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.ToString());
    }
    Console.Read();
}

在启动self-host的时候遇到如下的异常信息：

System.InvalidOperationException: Cannot have two operations in the same contract with the same name, methods Add and Add in type Server.ICalculator violate this rule. You can change the name of one of the operations by changing the method name or by using the Name property of OperationContractAttribute.

原因在于，基于wsdl的方法是不支持重载的，方法名是唯一的标识。WCF提供了一个解决方法，就是给[OperationContract]一个name属性。

[ServiceContract]
interface ICalculator
{
    [OperationContract(Name="AddInt")]
    int Add(int a, int b);
 
    [OperationContract(Name="AddDouble")]
    double Add(double a, double b);
}

 重新启动self-host以后，异常不再出现。从客户端角度来看，如果以channel的方式调用：

static void Main(string[] args)
{
    Binding binding = new WSHttpBinding();
    EndpointAddress address = new EndpointAddress("http://localhost:8086/Calculator/");
    ICalculator proxy = ChannelFactory<ICalculator>.CreateChannel(binding, address);
    using (proxy as IDisposable)
    {
        Console.WriteLine(proxy.Add(1, 2));
        Console.WriteLine(proxy.Add(1.0, 2.0));
    }
    Console.Read();
}

因为是引用了ICalculator接口，客户端也支持了面向对象语言的重载特性。但如果使用的自动生成的proxy类，会生成类似如下的类定义：

[ServiceContract]
interface ICalculator
{
    [OperationContract]
    int AddInt(int a, int b);
 
    [OperationContract]
    double AddDouble(double a, double b);
}
 
public partial class CalculatorClient : ClientBase<ICalculator>, ICalculator
{
    public int AddInt(int a, int b)
    {
        return Channel.AddInt(a, b);
    }
 
    public int AddDouble(double a, double b)
    {
        return Channel.AddDouble(a, b);
    }
}
.....

为了让代理类也支持重载特性，可以手工的修改代理：

[ServiceContract]
interface ICalculator
{
    [OperationContract(Name="AddInt")]
    int Add(int a, int b);
 
    [OperationContract(Name="AddDouble")]
    double Add(double a, double b);
}
 
public partial class CalculatorClient : ClientBase<ICalculator>, ICalculator
{
    public int Add(int a, int b)
    {
        return Channel.Add(a, b);
    }
 
    public int Add(double a, double b)
    {
        return Channel.Add(a, b);
    }
}
.....

然后我们在调用代理类的时候，可以同使用channel一样，使用重载特性啦。。。。

CalculatorClient proxy = new CalculatorClient ();
Console.WriteLine(proxy.Add(1, 2));
Console.WriteLine(proxy.Add(1.0, 2.0));
proxy.Close();