如何：以异步方式调用 WCF 服务操作

项目
02/28/2011

本主题介绍客户端如何以异步方式访问服务操作。本主题中的服务可实现 ICalculator 接口。通过使用事件驱动的异步调用模型，客户端可以对此接口异步调用操作。（有关基于事件的异步调用模型的更多信息，请参见Multithreaded Programming with the Event-based Asynchronous Pattern）。有关演示如何在服务中异步实现操作的示例，请参见如何：实现异步服务操作。有关同步操作和异步操作的更多信息，请参见同步和异步操作。

注意：
使用 ChannelFactory 时，不支持事件驱动的异步调用模型。有关使用 ChannelFactory 进行异步调用的信息，请参见如何：使用通道工厂以异步方式调用操作。

过程

以异步方式调用 WCF 服务操作

运行同时带有 /async 和 /tcv:Version35 命令选项的 ServiceModel 元数据实用工具 (Svcutil.exe) 工具，如下面的命令所示。

svcutil /n:http://Microsoft.ServiceModel.Samples,Microsoft.ServiceModel.Samples https://localhost:8000/servicemodelsamples/service/mex /a /tcv:Version35

除了同步操作和基于委托的标准异步操作之外，此操作还会生成 WCF 客户端类，其中包含以下内容：

两个与基于事件的异步调用方法一起使用的 <operationName>Async 操作。例如：

Public Overloads Sub AddAsync(ByVal n1 As Double, ByVal n2 As Double)
    Me.AddAsync(n1, n2, Nothing)
End Sub

Public Overloads Sub AddAsync(ByVal n1 As Double, ByVal n2 As Double, ByVal userState As Object)
    If (Me.onBeginAddDelegate Is Nothing) Then
        Me.onBeginAddDelegate = AddressOf Me.OnBeginAdd
    End If
    If (Me.onEndAddDelegate Is Nothing) Then
        Me.onEndAddDelegate = AddressOf Me.OnEndAdd
    End If
    If (Me.onAddCompletedDelegate Is Nothing) Then
        Me.onAddCompletedDelegate = AddressOf Me.OnAddCompleted
    End If
    MyBase.InvokeAsync(Me.onBeginAddDelegate, New Object() {n1, n2}, Me.onEndAddDelegate, Me.onAddCompletedDelegate, userState)
End Sub

public void AddAsync(double n1, double n2)
{
    this.AddAsync(n1, n2, null);
}

public void AddAsync(double n1, double n2, object userState)
{
    if ((this.onBeginAddDelegate == null))
    {
        this.onBeginAddDelegate = new BeginOperationDelegate(this.OnBeginAdd);
    }
    if ((this.onEndAddDelegate == null))
    {
        this.onEndAddDelegate = new EndOperationDelegate(this.OnEndAdd);
    }
    if ((this.onAddCompletedDelegate == null))
    {
        this.onAddCompletedDelegate = new System.Threading.SendOrPostCallback(this.OnAddCompleted);
    }
    base.InvokeAsync(this.onBeginAddDelegate, new object[] {
                n1,
                n2}, this.onEndAddDelegate, this.onAddCompletedDelegate, userState);
}

与基于事件的异步调用方法一起使用且形式为 <operationName>Completed 的操作完成事件。例如：

Public Event AddCompleted As System.EventHandler(Of AddCompletedEventArgs)

public event System.EventHandler<AddCompletedEventArgs> AddCompleted;

与基于事件的异步调用方法一起使用的每个操作的 System.EventArgs 类型（形式为 <operationName>CompletedEventArgs）。例如：

<System.Diagnostics.DebuggerStepThroughAttribute(),  _
 System.CodeDom.Compiler.GeneratedCodeAttribute("System.ServiceModel", "3.0.0.0")>  _
Partial Public Class AddCompletedEventArgs
    Inherits System.ComponentModel.AsyncCompletedEventArgs

    Private results() As Object

    Public Sub New(ByVal results() As Object, ByVal exception As System.Exception, ByVal cancelled As Boolean, ByVal userState As Object)
        MyBase.New(exception, cancelled, userState)
        Me.results = results
    End Sub

    Public ReadOnly Property Result() As Double
        Get
            MyBase.RaiseExceptionIfNecessary
            Return CType(Me.results(0),Double)
        End Get
    End Property
End Class

[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.CodeDom.Compiler.GeneratedCodeAttribute("System.ServiceModel", "3.0.0.0")]
public partial class AddCompletedEventArgs : System.ComponentModel.AsyncCompletedEventArgs
{
    private object[] results;

    public AddCompletedEventArgs(object[] results, System.Exception exception, bool cancelled, object userState) : 
            base(exception, cancelled, userState)
    {       this.results = results;         }

    public double Result
    {
        get            {
            base.RaiseExceptionIfNecessary();
            return ((double)(this.results[0]));
        }
    }
}

在调用应用程序中，创建一个要在异步操作完成时调用的回调方法，如下面的示例代码所示。

' Asynchronous callbacks for displaying results.
Private Shared Sub AddCallback(ByVal sender As Object, ByVal e As AddCompletedEventArgs)

    Console.WriteLine("Add Result: {0}", e.Result)

End Sub

// Asynchronous callbacks for displaying results.
static void AddCallback(object sender, AddCompletedEventArgs e)
{
    Console.WriteLine("Add Result: {0}", e.Result);
}

调用该操作之前，请使用 <operationName>EventArgs 类型的新泛型 System.EventHandler，将处理程序方法（在上一步中创建）添加到 <operationName>Completed 事件。然后，调用 <operationName>Async 方法。例如：

' AddAsync
Dim value1 As Double = 100
Dim value2 As Double = 15.99
AddHandler client.AddCompleted, AddressOf AddCallback
client.AddAsync(value1, value2)
Console.WriteLine("Add({0},{1})", value1, value2)

// AddAsync
double value1 = 100.00D;
double value2 = 15.99D;
client.AddCompleted += new EventHandler<AddCompletedEventArgs>(AddCallback);
client.AddAsync(value1, value2);
Console.WriteLine("Add({0},{1})", value1, value2);

示例

注意：
基于事件的异步模型设计准则规定，如果返回了多个值，则一个值会作为 Result 属性返回，其他值会作为 EventArgs 对象上的属性返回。因此产生的结果之一是，如果客户端使用基于事件的异步命令选项导入元数据，且该操作返回多个值，则默认的 EventArgs 对象返回一个值作为 Result 属性，返回的其余值是 EventArgs 对象的属性。如果要将消息对象作为 Result 属性来接收并要使返回的值作为该对象上的属性，请使用 /messageContract 命令选项。这会生成一个签名，该签名会将响应消息作为 EventArgs 对象上的 Result 属性返回。然后，所有内部返回值就都是响应消息对象的属性了。

基于事件的异步模型设计准则规定，如果返回了多个值，则一个值会作为 Result 属性返回，其他值会作为 EventArgs 对象上的属性返回。因此产生的结果之一是，如果客户端使用基于事件的异步命令选项导入元数据，且该操作返回多个值，则默认的 EventArgs 对象返回一个值作为 Result 属性，返回的其余值是 EventArgs 对象的属性。如果要将消息对象作为 Result 属性来接收并要使返回的值作为该对象上的属性，请使用 /messageContract 命令选项。这会生成一个签名，该签名会将响应消息作为 EventArgs 对象上的 Result 属性返回。然后，所有内部返回值就都是响应消息对象的属性了。

Imports System

Namespace Microsoft.ServiceModel.Samples

    ' The service contract is defined in generatedClient.vb, generated from the service by the svcutil tool.

    Class Client

        Public Shared Sub Main()

            Console.WriteLine("Press <ENTER> to terminate client once the output is displayed.")
            Console.WriteLine()

            ' Create a client
            Dim client As New CalculatorClient()

            ' AddAsync
            Dim value1 As Double = 100
            Dim value2 As Double = 15.99
            AddHandler client.AddCompleted, AddressOf AddCallback
            client.AddAsync(value1, value2)
            Console.WriteLine("Add({0},{1})", value1, value2)

            ' SubtractAsync
            value1 = 145
            value2 = 76.54
            AddHandler client.SubtractCompleted, AddressOf SubtractCallback
            client.SubtractAsync(value1, value2)
            Console.WriteLine("Subtract({0},{1})", value1, value2)

            ' Multiply
            value1 = 9
            value2 = 81.25
            Dim result As Double = client.Multiply(value1, value2)
            Console.WriteLine("Multiply({0},{1}) = {2}", value1, value2, result)

            ' Divide
            value1 = 22
            value2 = 7
            result = client.Divide(value1, value2)
            Console.WriteLine("Divide({0},{1}) = {2}", value1, value2, result)
            Console.ReadLine()

            'Closing the client gracefully closes the connection and cleans up resources
            client.Close()

        End Sub
        ' Asynchronous callbacks for displaying results.
        Private Shared Sub AddCallback(ByVal sender As Object, ByVal e As AddCompletedEventArgs)

            Console.WriteLine("Add Result: {0}", e.Result)

        End Sub
        Private Shared Sub SubtractCallback(ByVal sender As Object, ByVal e As SubtractCompletedEventArgs)

            Console.WriteLine("Subtract Result: {0}", e.Result)

        End Sub

    End Class

End Namespace

using System;

namespace Microsoft.ServiceModel.Samples
{
    // The service contract is defined in generatedClient.cs, generated from the service by the svcutil tool.

    class Client
    {
        static void Main()
        {
            Console.WriteLine("Press <ENTER> to terminate client once the output is displayed.");
            Console.WriteLine();

            // Create a client
            CalculatorClient client = new CalculatorClient();

            // AddAsync
            double value1 = 100.00D;
            double value2 = 15.99D;
            client.AddCompleted += new EventHandler<AddCompletedEventArgs>(AddCallback);
            client.AddAsync(value1, value2);
            Console.WriteLine("Add({0},{1})", value1, value2);

            // SubtractAsync
            value1 = 145.00D;
            value2 = 76.54D;
            client.SubtractCompleted += new EventHandler<SubtractCompletedEventArgs>(SubtractCallback);
            client.SubtractAsync(value1, value2);
            Console.WriteLine("Subtract({0},{1})", value1, value2);

            // Multiply
            value1 = 9.00D;
            value2 = 81.25D;
            double result = client.Multiply(value1, value2);
            Console.WriteLine("Multiply({0},{1}) = {2}", value1, value2, result);

            // Divide
            value1 = 22.00D;
            value2 = 7.00D;
            result = client.Divide(value1, value2);
            Console.WriteLine("Divide({0},{1}) = {2}", value1, value2, result);

            Console.ReadLine();

            //Closing the client gracefully closes the connection and cleans up resources
            client.Close();
        }

        // Asynchronous callbacks for displaying results.
        static void AddCallback(object sender, AddCompletedEventArgs e)
        {
            Console.WriteLine("Add Result: {0}", e.Result);
        }

        static void SubtractCallback(object sender, SubtractCompletedEventArgs e)
        {
            Console.WriteLine("Subtract Result: {0}", e.Result);
        }
    }
}

另请参见

任务

异步

通过

如何：以异步方式调用 WCF 服务操作

过程

以异步方式调用 WCF 服务操作

示例

另请参见

任务

其他资源