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Microsoft KB Archive/105658

From BetaArchive Wiki

Article ID: 105658

Article Last Modified on 10/11/2006



APPLIES TO

  • Microsoft Access 2.0 Standard Edition
  • Microsoft Access 95 Standard Edition



This article was previously published under Q105658

Advanced: Requires expert coding, interoperability, and multiuser skills.


SYMPTOMS

When you enter either the DDE() or the DDESend() function in the ControlSource property of a text box on a form, you may receive the following error message.

In Microsoft Access for Windows 95 version 7.0:

The expression you entered has an invalid string

In Microsoft Access version 2.0:

Syntax error in string

This article assumes that you are familiar with Visual Basic for Applications and with creating Microsoft Access applications using the programming tools provided with Microsoft Access. For more information about Visual Basic for Applications, please refer to the "Building Applications With Microsoft Access For Windows 95" manual.

NOTE: Visual Basic for Applications (used in Microsoft Access for Windows 95 version 7.0) is called Access Basic in version 2.0. For more information about Access Basic, please refer to the "Building Applications" manual.

CAUSE

A reference to another control is being used for the application or topic argument in the function. Note that you can successfully include a control reference for the item or data argument.

RESOLUTION

The following example demonstrates how to create and use the sample Visual Basic for Applications or Access Basic functions newDDE() and newDDESend() in place of the DDE() and DDESend() functions:

  1. Open a module and enter the following code:

          Option Explicit
    
          Function newDDE (App, Topic, Item)
    
             Dim chan
             On Error GoTo ErrnewDDE
             chan = DDEInitiate(App, Topic)
             newDDE = DDERequest(chan, Item)
             DDETerminate chan
    
          ByenewDDE:
             Exit Function
    
          ErrnewDDE:
             newDDE = "#DDEERROR"
             Resume ByenewDDE
    
          End Function
    
          Function newDDESend (App, Topic, Item, DataToSend)
             Dim chan
             On Error GoTo ErrnewDDESend
             chan = DDEInitiate(App, Topic)
             DDEPoke chan, Item, DataToSend
             DDETerminate chan
             newDDESend = True
    
          ByenewDDESend:
             Exit Function
    
          ErrnewDDESend:
             newDDESend = False
             Resume ByenewDDESend
    
          End Function
                        
  2. Start Microsoft Word for Windows, version 7.0. Save a new document as Test.
  3. Type a few lines of text in the document, and then select the text.
  4. Click Bookmark on the Edit menu. Type MyBookMark, and then press ENTER.
  5. Switch to Microsoft Access (leave Word for Windows running).
  6. Create a new form with the following controls and properties:

          Text box:
            Name: App
          Text box:
            Name: Topic
          Text box:
            Name: Item
          Text box:
            Name: Data
          Text box:
            Name: DDE
            ControlSource: =newDDE([App],[Topic],[Item])
          Text box:
            Name: DDESend
            ControlSource:
               =newDDESend([App],[Topic],[Item],[Data])
            Format: True/False
                        
  7. On the View menu, click Form. Note that "#DDEError" appears in the DDE text box, and "False" appears in the DDESend text box. These messages occur because there are not yet valid application, topic, and item arguments.
  8. Create the following entries:

    App: Winword
    Topic: Test
    Item: MyBookMark
    Data: Hello!

    Note that the DDESend box displays "True," and the text "Hello!" appears in the Word for Windows document.
  9. With the insertion point in the DDE box, press F9 to force the function to refresh. Note that "Hello!" appears in the DDE box in place of "#DDEError."


STATUS

This behavior is by design.

MORE INFORMATION

When the form is opened, Microsoft Access immediately establishes a DDE channel to the other application. This link uses the application and topic arguments in the function. The channel is kept open until the form is closed. Because the channel is open, the arguments necessary for opening the channel cannot be altered.

Microsoft Access does not open a new channel whenever it needs to call or refresh the control with the DDE() or DDESend() function. Doing so would impose significant overhead and could result in performance degradation.

Steps to Reproduce Behavior

  1. Create a blank, unbound form.
  2. Add a text box to the form.
  3. Enter any of the following expressions in the text box's ControlSource property:

    =DDE("winword",[topic],"my item")
    
          =DDE([app],"MyDoc","my item")
    
          =DDESend("winword",[topic],"my item, "my data")
    
          =DDESend([app],"MyDoc","my item, "my data")
                        

Note that you receive the error message mentioned earlier in this article. Any reference to another control in the application or topic argument will generate this error.

REFERENCES

For more information about sharing data between applications, search for "dynamic data exchange (DDE)," and then "Overview" using the Microsoft Access for Windows 95 Help Index.

Microsoft Access "User's Guide", version 2.0, pages 735, 740

Microsoft Access "Building Applications", version 2.0, pages 295-298

Keywords: kbprogramming KB105658