Consuming a Simple Web Service With .NET SDK

Summary

How to Consume a Web Service

To consume a Web Service within your application, you need to have the following:

The proxy is important because it hides the gory details of SOAP serialization and network communication: The proxy allows you to develop your application as if the Web Service resided locally on your computer. It serializes method request to SOAP and then sends the SOAP message to the Web Service via the network. After the Web Service has finished processing your request and returns its results encoded in a SOAP message, the proxy intercepts the message and deserializes it and returns the result to the calling application.

wsdl.exe is a .NET utility to generate code for Web Service clients and ASP.NET Web Services from WSDL contract files.  You use this tool to create a proxy for your Web Service so that you can use it in your Web Forms application. The following listing has been created for the pmcalc Web Service which was described in Creating Web Service With .NET SDK using the command:

wsdl.exe /l:CS http://localhost/pmcalc/pmcalc.asmx?wsdl

//------------------------------------------------------------------------------
// <autogenerated>
// This code was generated by a tool.
// Runtime Version: 1.0.2914.16
//
// Changes to this file may cause incorrect behavior and will be lost if 
// the code is regenerated.
// </autogenerated>
//------------------------------------------------------------------------------

// 
// This source code was auto-generated by wsdl, Version=1.0.2914.16.
// 
using System.Diagnostics;
using System.Xml.Serialization;
using System;
using System.Web.Services.Protocols;
using System.Web.Services;


/* Note that the class pmcalc inherits from System.Web.Services.Protocols.SoapHttpClientProtocol and then uses the this keyword
to refer to its instance */
[System.Web.Services.WebServiceBindingAttribute(Name="pmcalcSoap", Namespace="http://tempuri.org/")]
public class pmcalc : System.Web.Services.Protocols.SoapHttpClientProtocol
{

    /* Sets properties such as the URL when the class is instantiated*/
    [System.Diagnostics.DebuggerStepThroughAttribute()]
    public pmcalc() 
    {
        this.Url = "http://localhost/chapter2/pmcalc.asmx";
    }

    /* This Web Service has three methods. The first is Square which you use in your Web Services 
    applications. The next two methods, BeginSquare and EndSquare allow for asynchronous calls to
    the Web Service.
    When the Web Forms application calls the Square method, this class calls invoke on itself. This
    starts the serialization and transportation of your information over the network and also handles
    deserialization in the response to your call. All this functionality is encapsulated in the
    System.Web.Services.Protocols.SoapHttpClientProtocol class */
    [System.Diagnostics.DebuggerStepThroughAttribute()]
    [System.Web.Services.Protocols.SoapDocumentMethodAttribute("http://tempuri.org/Square",
    Use=System.Web.Services.Description.SoapBindingUse.Literal,
    ParameterStyle=System.Web.Services.Protocols.SoapParameterStyle.Wrapped)]
    public int Square(int nNum)
    {
        object[] results = this.Invoke("Square", new object[] {nNum});
        return ((int)(results[0]));
    }

    /* BeginSquare and EndSquare allow for asynchronous calls to the Web Service */    
    [System.Diagnostics.DebuggerStepThroughAttribute()]
    public System.IAsyncResult BeginSquare(int nNum, System.AsyncCallback callback, object asyncState)
    {
        return this.BeginInvoke("Square", new object[] {nNum}, callback, asyncState);
    }

    [System.Diagnostics.DebuggerStepThroughAttribute()]
    public int EndSquare(System.IAsyncResult asyncResult)
    {
        object[] results = this.EndInvoke(asyncResult);
        return ((int)(results[0]));
    }
}

Now that you have the source code to the proxy, you need to compile it into a .NET assembly using either the VB.NET compiler vbc.exe or C# compiler csc.exe. To compile the pmcalc.cs proxy class:

csc /out:bin\pmcalc.dll /target:library pmcalc.cs

Creating the Web Service Consumer

Now that you have created the proxy code file and compiled it into a .NET assembly, you need to create an ASP.NET Web Forms page to call your Web Service and display results to the user's Web browser. Note that in the following code you are not using typical HTML fields. Instead you are using ASP.NET server-side controls. When these tags are processed at the server (runat=server), the ASP.NET Web Forms HTML handler interprets and renders them as HTML. These server-side controls give you a high degree of programmability when creating your Web Forms applications. The following file is saved as default.aspx.

<html>
    <head>
    <title>Sample Web Service</title>
    <script Language=CSharp runat=server>
    public void btnGo_Click(Object Sender, System.EventArgs e)
    {
        // Note how we reference and call the Web Service as if were 
        // implemented locally on this machine. This is the purpose of
        // the proxy: to make method calls transparent to the 
        // user-programmer
        pmcalc o = new pmcalc();

        // Convert the entered number into Int32
        Int32 intNum;
        intNum = Convert.ToInt32(txtNumber.Text);

        // Invoke the Web Service via the proxy
        lblResult.Text = o.Square(intNum).ToString();
    }
    </script>
</head>

<body>
    <form runat=server>
        <p>Enter number: 
            <asp:textbox id=txtNumber size=5 runat=server />
            <asp:button id=btnGo text="Compute Square" runat=server onClick=btnGo_Click />
        </p>
        <p>Result = <asp:label id=lblResult runat=server/></p>
    </form>
</body>

</html>

Output Result:

Here is a quick summary of all files involved in this Web Service: