Returning a Structure from a Web Service

As the operations your web services perform become more complex, there will be many times when your service will return a structure that contains fields or an array of structures. The following ServerInfo web service returns a structure of type Server that contains specifics about the web server:

Structure Server   Dim OS As String   Dim DotNet As Boolean   Dim SSL As Boolean   Dim Administrator As String   Dim WebServer As String End Structure

The ServerInfo web service supports one method, GetInfo, as shown here:

Server GetInfo()

To create the ServerInfo web service, perform these steps:

1. Within Visual Studio .NET, select the File menu New Project option. Visual Studio .NET will display the New Project dialog box.

2. Within the New Project dialog box Project Types list, click Visual Basic Projects. Then, within the Templates field, click ASP.NET Web Service. Finally, within the Location field, specify the folder within which you want to store the program and the program name ServerInfo. Select OK. Visual Studio .NET will display a page onto which you can drag and drop the service’s components.

3. Select the View menu Code option. Visual Studio .NET will display the program’s source code. Within the source code add the following program statements:

       Structure Server         Dim OS As String         Dim DotNet As Boolean         Dim SSL As Boolean         Dim Administrator As String         Dim WebServer As String     End Structure     <WebMethod()> Public Function GetInfo() As Server         Dim Result As Server         Result.OS = "Windows"         Result.DotNet = True         Result.SSL = True         Result.Administrator = "B. Gates"         Result.WebServer = "IIS"         GetInfo = Result     End Function

4. After you enter the code, select the Build menu Build Solution option to create the service.

As you can see, the code simply assigns values to the structure variable and then returns the variable to calling program. Depending on your requirements, you might assign actual server values, similar to those contained in the actual .NET Server object.

Putting the ServerInfo Web Service to Use

The following Visual Basic .NET program, ShowSeverInfo.vb, uses the ServerInfo web server to retrieve specifics about a server. The program then displays the information within a form, as shown in Figure 2.13.

Figure 2.13: Using a web service method that returns a structure

To create the ShowServer.vb program, perform these steps:

1. Within Visual Studio .NET, select the File menu New Project option. Visual Studio .NET will display the New Project dialog box.

2. Within the New Project dialog box Project Types list, click Visual Basic Projects. Then, within the Templates field, click Windows Application. Within the Name and Location fields type ShowServer. Select OK. Visual Studio .NET will display a form onto which you can drag and drop the program’s controls (label, buttons, and text box).

3. Using the Toolbox, drag and drop the text box previously shown in Figure 2.13 onto the page.

4. Select the Project menu Add Web Reference option. Visual Studio .NET will display the Add Web Reference dialog box.

5. Within the Address field, type localhost/ServerInfo/Service1.asmx?WSDL and press Enter. The dialog box will load the file’s contents. Click the Add Reference button.

6. Select the View menu Code option. Visual Studio .NET will display the program’s source code. Within the source code add the following program statements:

       Private Sub Form1_Load(ByVal sender As System.Object, _ Ä   ByVal e As System.EventArgs) Handles MyBase.Load         Dim ServerObj As New localhost.Service1()         Dim Server As localhost.Server         Try             Server = ServerObj.GetInfo()             TextBox1.Text = "Server: "             TextBox1.Text &= Server.OS & vbCrLf             TextBox1.Text &= ".NET Support: "             TextBox1.Text &= Server.DotNet.ToString() & vbCrLf             TextBox1.Text &= "Admin: "             TextBox1.Text &= Server.Administrator & vbCrLf             TextBox1.Text &= "SSL support: "             TextBox1.Text &= Server.SSL.ToString() & vbCrLf             TextBox1.Text &= "Web Server: "             TextBox1.Text &= Server.WebServer & vbCrLf             TextBox1.Select(1, 0)         Catch Ex As Exception             TextBox1.Text = "Exception: " & Ex.Message         End Try     End Sub

To use a structure returned by a web service, the program must declare a variable to store the structure’s fields. Because the web service defines the structure’s format, the program declares a variable based on the structure type the service defines:

Dim Server As localhost.Server

In other words, the code creates an object it will use to interact with a service and also a variable that corresponds to the structure type the service returns:

Dim ServerObj As New localhost.Service1()  ' Interact with service Dim Server As localhost.Server    ' Structure defined by service

After the code calls the service, the code simply displays the structure’s contents (the structure fields) within a text box.