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Consuming a Web Service

The other end of this process is the consumption of the Web service, and it's just as easy to do. Using Visual Studio, we need only add a Web reference to the service to generate what's called a proxy class. A proxy class does what the name impliesit creates a code interface that acts as a front end to the remote code.

Proxy classes are generated in one of two ways in Visual Studio 2005. If you add a reference to a Web project, several files are generated that describe the service and how to discover it. The proxy class is then generated dynamically at runtime. If you add a Web reference to a class library project, an actual class is generated and added to the project.

For the moment, let's add a reference to a class library project. When you right-click on the project in the solution explorer and choose Add Web Reference, the dialog in Figure 10.2 appears.

The dialog has a mini-Web browser in it. Type the URL of the Web service, and the browser will attempt to identify it (don't forget the port number if you're using the built-in Web server of Visual Studio 2005). If the Web service is found, the dialog will indicate that on the right side and allow you to name the Web reference. The default is the domain name, but name it something you'll remember because it will be the root namespace used when you call it from code.

After you've added the reference, a number of files are added to the project. If you click the "show all files" button in the solution explorer and drill down under the Web references, you'll see a tree of files similar to those shown in Figure 10.3.

The most important file to look at is Reference.cs (or Reference.vb). This file contains the actual proxy class. The contents of the proxy class, generated based on the Web service, are shown in Listing 10.6. (We've left out the VB.NET version for the sake of brevity.)

Listing 10.6. The proxy class file generated for the EsteemBooster Web service

//--------------------------------------------------------------------
// <autogenerated>
//     This code was generated by a tool.
//     Runtime Version:2.0.40607.16
//
//     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 Microsoft.VSDesigner, Version 2.0.40607.16.
// 
namespace MyProject.Esteem {
using System.Diagnostics;
using System.Web.Services;
using System.ComponentModel;
using System.Web.Services.Protocols;
using System;
using System.Xml.Serialization;
/// <remarks/>
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Web.Services.WebServiceBindingAttribute(Name="EsteemBoosterSoap", Namespace="http:
//esteemshack/booster")]
public class EsteemBooster : System.Web.Services.Protocols.SoapHttpClientProtocol {
/// <remarks/>
public EsteemBooster() {
string urlSetting = System.Configuration.ConfigurationSettings
.AppSettings["MyProject.Esteem.EsteemBooster"];
if ((urlSetting != null)) {
this.Url = string.Concat(urlSetting, ");
}
else {
this.Url = "http://localhost:28680/textbox/EsteemBooster.asmx";
}
}
/// <remarks/>
[System.Web.Services.Protocols.SoapDocumentMethodAttribute("http://esteemshack/booster
/Boost", RequestNamespace="http://esteemshack/booster", ResponseNamespace="http:/
/esteemshack/booster", Use=System.Web.Services.Description.SoapBindingUse.Literal,
 ParameterStyle=System.Web.Services.Protocols.SoapParameterStyle.Wrapped)]
public Status Boost(Person peep) {
object[] results = this.Invoke("Boost", new object[] {
peep});
return ((Status)(results[0]));
}
/// <remarks/>
public System.IAsyncResult BeginBoost(Person peep, System.AsyncCallback callback,
 object asyncState) {
return this.BeginInvoke("Boost", new object[] {
peep}, callback, asyncState);
}
/// <remarks/>
public Status EndBoost(System.IAsyncResult asyncResult) {
object[] results = this.EndInvoke(asyncResult);
return ((Status)(results[0]));
}
}
/// <remarks/>
[System.SerializableAttribute()]
[System.Xml.Serialization.XmlTypeAttribute(Namespace="http://esteemshack/booster")]
public class Person {
/// <remarks/>
public string Name;
/// <remarks/>
public int Age;
}
/// <remarks/>
[System.SerializableAttribute()]
[System.Xml.Serialization.XmlTypeAttribute(Namespace="http://esteemshack/booster")]
public class Status {
/// <remarks/>
public string Message;
/// <remarks/>
public int Dollars;
}
}

For the most part, this generated class looks a lot like your Web service code, only with additional attributes and extra methods to do asynchronous calls to the service. The only thing missing is the actual codethe creation and calculation of a Status object, based on a Person object.

This code is generated based on the description offered by the Web Service Definition Language (WSDL). This is XML that describes the form of the XML data exchanged via the Web service. When you add a Web reference, Visual Studio checks the address you entered for this WSDL file. For Web services authored in .NET, you can simply append "?WSDL" to the end of an address to view the WSDL.

Let's add a new page to the Web project we created for our EsteemBooster service. Add a Web reference to the project. If you right-click the EsteemBooster.asmx file in the solution explorer and then click "show in browser," the resulting browser will have the address of the Web service. Use that for your reference. Remember that no proxy class file is generated in a Web project, though you'll still be able to reference the Web service classes and members, starting with the name you gave it (in the previous example we used "Esteem").

Now, in your new page, enter the code in Listing 10.7. Run the page (right-click and select Show in Browser from the solution explorer), and you'll get the resulting page shown in Figure 10.4.

Listing 10.7. A page that calls our Web service

C#

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<%@ Page Language="C#" %>
<script runat="server">
void LinkButton1_Click(object sender, EventArgs e)
{
Esteem.Person peep = new Esteem.Person();
peep.Name = NameTextBox.Text;
peep.Age = Convert.ToInt32(AgeTextBox.Text);
Esteem.EsteemBooster booster = new Esteem.EsteemBooster();
Esteem.Status status = booster.Boost(peep);
ResultLabel.Text = "Message: " + status.Message + " - Dollars: " + status.Dollars
.ToString("c");
}
</script>
<html>
<body>
<form id="form1" runat="server">
Name: <asp:TextBox ID="NameTextBox" Runat="server" /><br />
Age: <asp:TextBox ID="AgeTextBox" Runat="Server" /><br />
<asp:LinkButton ID="LinkButton1" Runat="server" OnClick="LinkButton1_Click">Get
 Message</asp:LinkButton><br />
<asp:Label ID="ResultLabel" Runat="Server" />
</form>
</body>
</html>

VB.NET

<%@ Page Language="VB" %>
<script runat="server">
Sub LinkButton1_Click(sender As Object, e As EventArgs)
Dim peep As New Esteem.Person()
peep.Name = NameTextBox.Text
peep.Age = Convert.ToInt32(AgeTextBox.Text)
Dim booster As New Esteem.EsteemBooster()
Dim status As Esteem.Status = booster.Boost(peep)
ResultLabel.Text = "Message: " + status.Message + _
" - Dollars: " + status.Dollars.ToString("c")
End Sub</script>
<html>
... (same as C# version
</html>

The code in the page has an event handler for the LinkButton that first creates a new Person object. That object is populated, an EsteemBooster object is created, and its Boost() method is called, passing in the Person object and assigning the returned Status object to a new variable. The results are displayed. This code doesn't look much different than if you were programming with the original classes in the Web services.