Access Cookbook, 2nd Edition [Electronic resources] نسخه متنی

Recipe 17.4 Call a Web Service from Access

17.4.1 Problem

A web service is a specially constructed
component that you can access over standard web protocols. To call a
web service, however, you must pass it messages encoded using
Simple Object Access Protocol (SOAP).
Access does not directly support the SOAP protocol. Is there any way
to call a web service from Access?

17.4.2 Solution

Microsoft has released several toolkits that can be used by Microsoft
Office programmers to call web services. This solution assumes you
are using Access 2003 with Microsoft Office 2003 Web
Services Toolkit. See the discussion section of this topic on calling
web services from earlier versions of Access.

The RunnerCalculator web service contains a
number of methods that provide pacing calculations for long distance
running. This web service can be found at www.deeptraining.com/webservices. One of the
RunnerCalculator methods, GetPaceDouble, can be
used to calculate the pace in minutes per mile for a given distance
and total time. Follow these steps to create an Access 2003 form that
uses this web service to calculate pace for a user-entered distance
and time:

1. 
   If you haven't yet done so, download and install the
   Microsoft Office 2003 Web Services Toolkit.

   
   

2. 
   Start Access 2003 and create an unbound form named
   frmPaceCalculator.

   
   

3. 
   Add the controls to the form listed in Table 17-1:

   
   

4. 
   From the VBA editor, select Tools Web Service
   References.... This menu item is added to the VBA editor by the
   Microsoft Office 2003 Web Services Toolkit.

   
   

5. 
   At the Microsoft Office 2003 Web Services Toolkit dialog box, select
   the Web Service URL radio button and enter the following address into
   the URL textbox:

   
   

   www.deeptraining.com/webservices/runnercalculator.asmx

6. 
   The RunnerCalculator service and its methods should be displayed in
   the SearchResults box. Check the checkbox to the left of
   RunnerCalculator and click the Add button at the bottom of the dialog
   box to add a reference to the RunnerCalculator service. The Microsoft
   Office 2003 Web Services Toolkit dialog box is shown in Figure 17-6.

   
   

Figure 17-6. You use the Microsoft Office 2003 Web Services Toolkit dialog box to locate a web service and set a reference to it

7. 
   The toolkit adds a new class module to the Access project with the
   name clsws_RunnerCalculator. This class serves as
   a proxy for making calls to the web service. The code in this class
   will take care of speaking to the web service using the SOAP
   protocol.

   
   

8. 
   Attach the following code to the cmdCalculatePace
   button's Click event to use the proxy class to call
   the RunnerCalculator web service:

   
   

   Private Sub cmdCalculatePace_Click( )
   Dim prxRunnerCalc As clsws_RunnerCalculator
   Dim strResult As String
   On Error GoTo HandleErr
   DoCmd.Hourglass True
   ' Instantiate proxy class
   Set prxRunnerCalc = New clsws_RunnerCalculator
   If Len(txtDistance) > 0 And Len(txtHours) > 0 And _
   Len(txtMinutes) > 0 And Len(txtSeconds) > 0 Then
   ' Call GetPaceString method via proxy class
   strResult = prxRunnerCalc.wsm_GetPaceString(txtDistance, _
   txtHours, txtMinutes, txtSeconds)
   lblPace.Caption = "Average Mile Pace: " & strResult
   Else
   MsgBox "You must enter values for each text box.", _
   vbOKOnly + vbCritical, "Pace Calculator"
   End If
   ExitHere:
   On Error GoTo 0
   DoCmd.Hourglass False
   Exit Sub
   HandleErr:
   MsgBox "Error " & Err.Number & ": " & Err.Description, _
   vbOKOnly + vbCritical, "Pace Calculator"
   Resume ExitHere
   End Sub

9. 
   Save the form and open it in form view. Enter values into each of the
   textboxes and click on the Calculate Pace button. The form should
   look like the one shown in Figure 17-7.

   
   

Figure 17-7. When you click on the Calculate Pace button, code behind the button calls the proxy class, which calls the RunnerCalculator web service

17.4.3 Discussion

When you set a reference to a web service using the Microsoft Office
2003 Web Services Toolkit, the toolkit creates a proxy class with the
name clsws_webservice,
where

webservice is the name of the web
service. The proxy class takes care of calling
the web service using SOAP and processing the response, again using
the SOAP protocol.

For every method of a web service, the Microsoft Office 2003 Web
Services Toolkit creates a corresponding method of the proxy class
with the name wsm_

method ,
where

method is the name of the web service
method. Thus, calling the web service is as simple as instantiating
the proxy class and calling the proxy method corresponding to the
method in the web service.

17.4.3.1 Calling web services from earlier versions of Access

If you wish to call a web service from Access XP or an
earlier version of Access the solution steps will differ from those
shown here. If you're using Access 2002, you need to
download and install the Microsoft Office XP Web Services Toolkit
2.0. The steps to use the Office XP toolkit are fairly similar to
using the Office 2003 toolkit. If you need to call a web service from
Access 2000 or an earlier version of Access, you'll
need to use the Microsoft SOAP Toolkit 3.0. This toolkit is geared
more towards Visual Studio 6.0 developers, but can also be used from
VBA code.

17.4.3.2 Locating the toolkits

The Microsoft Office 2003 Web Services
Toolkit can be found at http://www.microsoft.com/downloads/details.aspx? FamilyID=fa36018a-e1cf-48a3-9b35-169d819ecf18&DisplayLang=en.

The Microsoft Office XP Web Services Toolkit 2.0
can be found at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnxpwst2/html/odc_offxpwstoolkit2.asp.

The Microsoft SOAP Toolkit 3.0 can be found at
http://msdn.microsoft.com/library/default.asp?URL=/downloads/list/websrv.asp.

17.4.4 See Also

Integrating XML Web Services Into Microsoft
Office Solutions (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnofftalk/html/office09062001.asp).