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CHAPTER 9 XML WEB SERVICE S
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Figure 9-10. The Add Web Reference dialog box A web reference is nothing but a proxy class that allows you to use classes and methods exposed by a web service in your client application. In this dialog box, enter the complete URL of the Service.asmx file and click the Go button. You will see the same help page as before. In the Web Reference Name text box, key in a name for the web reference or leave it unchanged. Whatever you supply in this text box becomes the namespace name for the proxy class being created. Click the Add Reference button. Your Solution Explorer should now look like Figure 9-11.
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Figure 9-11. Web References folder
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C H APTE R 9 XM L WEB S ERVI CES
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Note how a new folder called Web References has been added with a subfolder called localhost. The localhost folder further contains a WSDL file. There will also be a file called Reference.cs. This file contains the source code of the web service proxy class. If you change the web service after adding the proxy, you need to update the web reference again. You can do so by right-clicking the web reference and selecting the Update Web Reference option.
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Creating a Form That Consumes a Web Method
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To demonstrate how to call web methods, you will need to create a form that will display the records from the Employees table. The form should look like Figure 9-12.
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Figure 9-12. Application that calls the GetEmployees() web method The application consists of a DataGridView control that displays all the records from the Employees table of the Northwind database. Import the localhost namespace in your project (recollect that we have specified the web reference name as localhost). In the Load event of the form, write the code shown in Listing 9-15. Listing 9-15. Calling a Web Method private void Form1_Load(object sender, EventArgs e) { Service proxy = new Service(); DataSet ds = proxy.GetEmployees(); dataGridView1.DataSource = ds.Tables["myemployees"].DefaultView; } The code creates an instance of the proxy class. Note that Service is the proxy class, not the web service class itself. We then call the GetEmployees() method of the proxy, which in turn will call the actual GetEmployees() web method of the web service. Remember that the return value of GetEmployees() is a DataSet populated with records from the Employees table. The code then binds the DataSet to the DataGridView. If you run the application, you should see the DataGridView populated with records from the Employees table.
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CHAPTER 9 XML WEB SERVICE S
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Storing Values in a Web Service Session
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Recollect that earlier we created two web methods PutNameInSession() and GetNameFromSession() that deal with session storage. Let s see how you can call these methods in the client application. To see how this works, you need to create an application like the one shown shown in Figure 9-13.
Figure 9-13. Storing session values The application consists of a text box and two buttons. The text box accepts a name that is to be stored in a session variable. The Store Name in Session button calls the PutNameInSession() web method and stores the name in a session variable. The Retrieve Name from Session button calls the GetNameFromSession() web method and displays the returned name in a message box. Listing 9-16 shows the code that is responsible for storing the name in a session variable. Listing 9-16. Storing a Value in a Session Variable CookieContainer cookiecontainer = new CookieContainer(); private void button1_Click(object sender, EventArgs e) { Service proxy = new Service(); proxy.CookieContainer = cookiecontainer; proxy.PutNameInSession(textBox1.Text); } The code creates a form-level variable of type CookieContainer, which resides in the System.Net namespace and acts as storage for cookies. You might be wondering why we need this class. By default the session management of web services depends on a cookie, and the web service needs to identify each and every session with the help of a unique identifier. This identifier is passed to and fro with the help of a cookie. The code then creates an instance of the web service proxy class. It sets its CookieContainer property to the CookieContainer object we just created. The CookieContainer property of the proxy class specifies the storage for the cookies created during the web service communication. Finally, the code calls the PutNameInSession() method of the proxy by passing the name entered in the text box. The Click event handler of the Retrieve Name from Session button contains the code shown in Listing 9-17.
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