Tài liệu Consume XML Web Services ppt

13.3 Consume XML Web Services
I have created this Web Service that takes the username and password and returns True or
False based on whether the username and password check out. I have even tested the
Web Service to make sure it works correctly. How do I use, or consume, this Web
Service in another application?
Technique
To use a Web Service, you need to create a reference to it.
Setting Up the Web Reference to the Web Service
To set up a Web reference, you choose Add Web Reference from the Project menu. You
are then presented with the Add Web Reference dialog box, which allows you to browse
for Web Services using the Universal Description Discovery Integration (UDDI)
directories, as described in the beginning of the chapter. However, you will be able to
browse to the Web Service you created and supply the name of the full URL using
localhost to the name of the .asmx file you created, in this case:
http://localhost/securitywebservice/SecurityServices.asmx
After you have specified this, you will see the methods appear for your Web Service (see
Figure 13.11.)
Figure 13.11. You can test the Web Service right in this dialog box.

Note
You can see two methods for this Web Service: TestUserPassword and
GetUserInfo. The second method is discussed in How-To 13.4.

After you have clicked Add Reference to accept the new reference, you can use the
methods in your application. You can double-check that the reference is there by looking
for it under the Web Reference node that appears in the Solution Explorer (see Figure
13.12.)
Figure 13.12. You can see the reference created in the Solution Explorer.

Calling Web Service Methods
After you have created the reference to the Web Service, you will create a reference
within your application, much like you would to other object models. Following is a
snippet of code that performs this very task:
Dim wsSec As localhost.SecurityServices

wsSec = New localhost.SecurityServices()

If wsSec.TestUserPassword(Me.txtUser.Text, Me.txtPassword.Text) Then
As you can see, the method TestUserPassword is called just as another other method or
function is called.
Steps
To preview this How-To, open the solution called Visual Basic .NET-Chapter 13, located
in the chapter folder.
Note

You will probably have to re-establish the Web reference for the Web
Service that is used for this example. Locate where you have installed
SecurityWebServices and set the reference.

When you run the project, the first form that comes up is the main switchboard with each
of the How-Tos listed for this chapter. Click on How-To 13.3. The form for How-To 13.3
opens.
If you type FSBarker for the User and Test for the Password, you get a message box
telling you that you can continue into the application (see Figure 13.13).
1. Create a new Visual Studio .NET project using the Windows Application project
template. Create a Windows Form, and place the controls shown in Table 13.1 in
the order displayed in Figure 13.13.
Table 13.1. Label, TextBox, and Command Button Control Property Settings
Object Property Setting

Label Text User
TextBox Name txtUser
Label Text Password
TextBox Name txtPassword
Button Name btnLogin
2. As described in the "Technique" section, set a reference to the Web Service you
created in the previous How-To. Remember to point to the *.asmx file created in
the Web Service. Choose Add Web Reference from the Project menu.
3. Add the code listed in Listing 13.3 to the Click event of btnLogin by double-
clicking on the button. This routine instantiates an instance of the Web Service.
Then, using the wsSec object, the routine calls the TestUserPassword method.
This method is passed the username and password that were entered.
Listing 13.3 frmHowTo13_3.vb: Web Method to Validate Username and
Password
Private Sub btnLogin_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles btnLogin.Click

Dim wsSec As localhost.SecurityServices

wsSec = New localhost.SecurityServices()

If wsSec.TestUserPassword(Me.txtUser.Text, Me.txtPassword.Text) Then
MessageBox.Show("You may go into the applcation.")
Else
MessageBox.Show("You may not go into the application.")
End If

End Sub
Figure 13.13. This login form takes advantage of a Web Service for authentication.

Comment
Note that passing parameters and using the return value is just like using methods from
other objects or even functions from your own applications.