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

Ken Getz; Paul Litwin; Andy Baron

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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:




Table 17-1. Controls for frmPaceCalculator


Control




Name




TextBox




txtDistance




TextBox




txtHours




TextBox




txtMinutes




TextBox




txtSeconds




CommandButton




cmdCalculatePace




Label




lblPace




  1. 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.



  2. 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

  3. 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




  1. 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.



  2. 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

  3. 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).



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