Proxy classes are generated using the wsdl.exe tool, included with the .NET Framework and located in the C:Program FilesMicrosoft Visual Studio .NETFrameworkSDKBin folder. The wsdl tool provides the command-line options described in Table 19-6.

The following statement illustrates how to create a proxy for the example SumService XML Web service developed earlier in this chapter, accepting the default settings for the command-line options:

wsdl http://localhost/SumService/SumService.asmx

The statement generates a C# source file named Sum.cs containing a proxy class for the XML Web service.

Proxy classes can be created for XML Web services that haven’t been created with .NET; the URL that is passed to the wsdl.exe tool must point to the WSDL document for the service.

Using a proxy class is no different from using any other class. The following example demonstrates a class that relies on the proxy just created, which we have saved in a source file named SumClient.cs:

public class SumClient {

    static void Main(string[] p_args) {
        Sum x_sum = new Sum();
        int x_result = x_sum.sumNumbers(10, 20);
        System.Console.WriteLine("Result: " + x_result);
    }
}

The statements related to the proxy class are marked in boldface. We create a new instance of the Sum proxy class and invoke the sumNumbers method. Each of the methods exposed by the XML Web service is represented by a C# method. The client class and the proxy are compiled using the following statement:

csc /out:SumClient.exe SumClient.cs Sum.cs

This statement creates an executable named SumClient.exe, which will automatically invoke the XML Web service as required.

Executing the SumClient application will generate the following output:

Result: 30

For each XML Web service method, three methods are automatically created in the proxy class, as described in Table 19-7.

Using the synchronous method is shown in the preceding section; this section deals with using XML Web services asynchronously, which follows the general model for all .NET asynchronous features.

The following example shows a client that makes asynchronous use of the example XML Web service:

using System;

public class AsyncSumClient {

    static void Main(string[] p_args) {
        Sum x_sum = new Sum();
        AsyncCallback x_callback =
            new AsyncCallback(AsyncSumClient.SumCallBack);
        x_sum.BeginsumNumbers(10, 20, x_callback, x_sum);

        Console.ReadLine();
    }

    static void SumCallBack(IAsyncResult p_callback) {
        Sum x_sum = (Sum)p_callback.AsyncState;
        int x_result = x_sum.EndsumNumbers(p_callback);
        System.Console.WriteLine("Result: " + x_result);
    }
}

The statements that relate to asynchronous support are marked in boldface. The request is started by calling the BeginsumNumbers method, passing in the arguments to the Web method, a delegate that references the SumCallBack method, and the instance of the proxy class that is being used. When the request has completed, the SumCallBack method is invoked, and we use the AsyncState property of the IAsyncResult to obtain the instance of the proxy class; the results of the request are obtained by calling the EndsumNumbers method.