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如何：创建双工协定

  • 项目

本主题演示了创建使用双工（双向）协定的方法所需的基本步骤。双工协定使得客户端和服务器可以独立地相互通信，这样双方都可以启动对另一方的呼叫。双工协定是可供 Windows Communication Foundation (WCF) 服务使用的三种消息模式之一。另外两种消息模式是单向模式和请求-答复模式。双工协定由客户端和服务器之间的两个单向协定组成，并且不需要方法调用是相关的。当服务必须向客户端查询更多信息或在客户端上显式引发事件时，可使用这种协定。有关创建用于双工协定的客户端应用程序的更多信息，请参见如何：使用双工协定访问服务。有关可运行的示例，请参见双工示例。

创建双工协定

  1. 创建组成双工协定的服务器方的接口。

  2. 将 ServiceContractAttribute 类应用到该接口。

    <ServiceContract(Namespace:="http://Microsoft.ServiceModel.Samples", SessionMode:=SessionMode.Required, _
                CallbackContract:=GetType(ICalculatorDuplexCallback))> _
Public Interface ICalculatorDuplex

    <OperationContract(IsOneWay:=True)> _
    Sub Clear()
    <OperationContract(IsOneWay:=True)> _
    Sub AddTo(ByVal n As Double)
    <OperationContract(IsOneWay:=True)> _
    Sub SubtractFrom(ByVal n As Double)
    <OperationContract(IsOneWay:=True)> _
    Sub MultiplyBy(ByVal n As Double)
    <OperationContract(IsOneWay:=True)> _
    Sub DivideBy(ByVal n As Double)
End Interface

    [ServiceContract(Namespace = "http://Microsoft.ServiceModel.Samples", SessionMode=SessionMode.Required,
                 CallbackContract=typeof(ICalculatorDuplexCallback))]
public interface ICalculatorDuplex
{
    [OperationContract(IsOneWay=true)]
    void Clear();
    [OperationContract(IsOneWay = true)]
    void AddTo(double n);
    [OperationContract(IsOneWay = true)]
    void SubtractFrom(double n);
    [OperationContract(IsOneWay = true)]
    void MultiplyBy(double n);
    [OperationContract(IsOneWay = true)]
    void DivideBy(double n);
}

  3. 在接口中声明方法签名。

  4. 将 OperationContractAttribute 类应用于每个方法签名，该方法签名必须是公共协定的一部分。

  5. 创建回调接口以定义服务可以在客户端上调用的操作组。

    Public Interface ICalculatorDuplexCallback
    <OperationContract(IsOneWay:=True)> _
    Sub Equals(ByVal result As Double)
    <OperationContract(IsOneWay:=True)> _
    Sub Equation(ByVal eqn As String)
end interface 

    public interface ICalculatorDuplexCallback
{
    [OperationContract(IsOneWay = true)]
    void Equals(double result);
    [OperationContract(IsOneWay = true)]
    void Equation(string eqn);
}

  6. 在回调接口中声明方法签名。

  7. 将 OperationContractAttribute 类应用于每个方法签名，该方法签名必须是公共协定的一部分。

  8. 通过将主接口中的 CallbackContract 属性设置为回调接口的类型，将两个接口链接到一个双工协定中。

在客户端上调用方法

  1. 在主协定的服务实现中，声明回调接口的变量。

  2. 将变量设置为通过 OperationContext 类的 GetCallbackChannel 方法返回的对象引用。

    Dim callback As ICalculatorDuplexCallback

    ICalculatorDuplexCallback callback = null;

    callback = OperationContext.Current.GetCallbackChannel(Of ICalculatorDuplexCallback)()

    callback = OperationContext.Current.GetCallbackChannel<ICalculatorDuplexCallback>();

  3. 调用由回调接口定义的方法。

示例

下面的代码示例演示双工通信。服务的协定包含用于向前移动和向后移动的服务操作。客户端的协定包含用于报告其位置的服务操作。

' Define a duplex service contract.
' A duplex contract consists of two interfaces.
' The primary interface is used to send messages from client to service.
' The callback interface is used to send messages from service back to client.
' ICalculatorDuplex allows one to perform multiple operations on a running result.
' The result is sent back after each operation on the ICalculatorCallback interface.
<ServiceContract(Namespace:="http://Microsoft.ServiceModel.Samples", SessionMode:=SessionMode.Required, _
                CallbackContract:=GetType(ICalculatorDuplexCallback))> _
Public Interface ICalculatorDuplex

    <OperationContract(IsOneWay:=True)> _
    Sub Clear()
    <OperationContract(IsOneWay:=True)> _
    Sub AddTo(ByVal n As Double)
    <OperationContract(IsOneWay:=True)> _
    Sub SubtractFrom(ByVal n As Double)
    <OperationContract(IsOneWay:=True)> _
    Sub MultiplyBy(ByVal n As Double)
    <OperationContract(IsOneWay:=True)> _
    Sub DivideBy(ByVal n As Double)
End Interface

' The callback interface is used to send messages from service back to client.
' The Equals operation will return the current result after each operation.
' The Equation opertion will return the complete equation after Clear() is called.
Public Interface ICalculatorDuplexCallback
    <OperationContract(IsOneWay:=True)> _
    Sub Equals(ByVal result As Double)
    <OperationContract(IsOneWay:=True)> _
    Sub Equation(ByVal eqn As String)
end interface 

' Service class which implements a duplex service contract.
' Use an InstanceContextMode of PerSession to store the result
' An instance of the service will be bound to each duplex session
<ServiceBehavior(InstanceContextMode:=InstanceContextMode.PerSession)> _
Public Class CalculatorService
    Implements ICalculatorDuplex
    Dim result As Double
    Dim equation As String
    Dim callback As ICalculatorDuplexCallback

    Public Sub New()
        result = 0D
        equation = result.ToString()
        callback = OperationContext.Current.GetCallbackChannel(Of ICalculatorDuplexCallback)()

    End Sub
    Public Sub AddTo(ByVal n As Double) Implements ICalculatorDuplex.AddTo
        result += n
        equation += " + " + n.ToString()
        callback.Equals(result)
    End Sub

    Public Sub Clear() Implements ICalculatorDuplex.Clear
        callback.Equation(equation + " = " + result.ToString())
        result = 0D
        equation = result.ToString()
    End Sub

    Public Sub DivideBy(ByVal n As Double) Implements ICalculatorDuplex.DivideBy
        result /= n
        equation += " / " + n.ToString()
        callback.Equals(result)
    End Sub

    Public Sub MultiplyBy(ByVal n As Double) Implements ICalculatorDuplex.MultiplyBy
        result *= n
        equation += " * " + n.ToString()
        callback.Equals(result)
    End Sub

    Public Sub SubtractFrom(ByVal n As Double) Implements ICalculatorDuplex.SubtractFrom
        result -= n
        equation += " - " + n.ToString()
        callback.Equals(result)
    End Sub
End Class

// Define a duplex service contract.
// A duplex contract consists of two interfaces.
// The primary interface is used to send messages from client to service.
// The callback interface is used to send messages from service back to client.
// ICalculatorDuplex allows one to perform multiple operations on a running result.
// The result is sent back after each operation on the ICalculatorCallback interface.
[ServiceContract(Namespace = "http://Microsoft.ServiceModel.Samples", SessionMode=SessionMode.Required,
                 CallbackContract=typeof(ICalculatorDuplexCallback))]
public interface ICalculatorDuplex
{
    [OperationContract(IsOneWay=true)]
    void Clear();
    [OperationContract(IsOneWay = true)]
    void AddTo(double n);
    [OperationContract(IsOneWay = true)]
    void SubtractFrom(double n);
    [OperationContract(IsOneWay = true)]
    void MultiplyBy(double n);
    [OperationContract(IsOneWay = true)]
    void DivideBy(double n);
}
// The callback interface is used to send messages from service back to client.
// The Equals operation will return the current result after each operation.
// The Equation opertion will return the complete equation after Clear() is called.
public interface ICalculatorDuplexCallback
{
    [OperationContract(IsOneWay = true)]
    void Equals(double result);
    [OperationContract(IsOneWay = true)]
    void Equation(string eqn);
}
// Service class which implements a duplex service contract.
// Use an InstanceContextMode of PerSession to store the result
// An instance of the service will be bound to each duplex session
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]
public class CalculatorService : ICalculatorDuplex
{
    double result;
    string equation;
    ICalculatorDuplexCallback callback = null;

    public CalculatorService()
    {
        result = 0.0D;
        equation = result.ToString();
        callback = OperationContext.Current.GetCallbackChannel<ICalculatorDuplexCallback>();
    }

    public void Clear()
    {
        callback.Equation(equation + " = " + result.ToString());
        result = 0.0D;
        equation = result.ToString();
    }

    public void AddTo(double n)
    {
        result += n;
        equation += " + " + n.ToString();
        callback.Equals(result);
    }

    public void SubtractFrom(double n)
    {
        result -= n;
        equation += " - " + n.ToString();
        callback.Equals(result);
    }

    public void MultiplyBy(double n)
    {
        result *= n;
        equation += " * " + n.ToString();
        callback.Equals(result);
    }

    public void DivideBy(double n)
    {
        result /= n;
        equation += " / " + n.ToString();
        callback.Equals(result);
    }

}

  • 应用 ServiceContractAttribute 和 OperationContractAttribute 属性允许自动生成使用 Web 服务描述语言 (WSDL) 的服务协定定义。

  • 使用 ServiceModel 元数据实用工具 (Svcutil.exe) 检索 WSDL 文档和（可选）代码以及客户端的配置。

  • 公开双工服务的终结点必须是安全的。当服务接收双工消息时，它会查看传入消息中的 ReplyTo，以确定要发送答复的位置。如果通道不安全，则不受信任的客户端可能使用目标计算机的 ReplyTo 发送恶意消息，从而导致目标计算机发生拒绝服务。对于常规的规则请求-答复消息，这不是问题，因为将会忽略 ReplyTo 并在传入原始消息的通道上发送响应。

另请参见

任务

如何：使用双工协定访问服务
双工
如何：定义 Windows Communication Foundation 服务协定
会话

参考

ServiceContractAttribute
OperationContractAttribute

概念

设计和实现服务