Microsoft KB Archive/137023

Knowledge Base

PRB: Can't See Changed Data If Update VB 3.0 DB App to VB 4.0

Article ID: 137023

Article Last Modified on 11/18/2003

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APPLIES TO

• Microsoft Visual Basic 4.0 Enterprise Edition
• Microsoft Visual Basic 3.0 Professional Edition
• Microsoft Visual Basic 3.0 Professional Edition

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This article was previously published under Q137023

SYMPTOMS

Applications written and compiled in Visual Basic 3.0 that check and reflect a changing data source do not show changed records after that application is compiled Visual Basic 4.0.

RESOLUTION

This problem does not occur if you occasionally call the Idle method of the DBEngine object using this line of code:

   DBEngine.Idle dbFreeLocks
                

This line of code is needed only for databases saved in Microsoft Jet versions 1.x and 2.x. Databases created with Microsoft Jet version 3.0 do not exhibit this behavior, and programs written only to manipulate Jet 3.0 databases do not require the call to the Idle method.

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Behavior

1. Start a new project in Visual Basic. Form1 is created by default.
2. Double-click the Label button in the Toolbox to add a label control (Label1) to Form1.
3. Add a timer control (Timer1) to Form1 by double-clicking the Timer button in the Toolbox.

4. Insert the following code in the General Declarations section of Form1:

      Dim db As Database
      Dim ds As Recordset
                           

5. Add the following code to the Form_Load and Form_Unload event procedures:

      Private Sub Form_Load()
         ' Replace the next line with the path to your VB 4.0 directory:
         Set db = DBEngine(0).OpenDatabase("c:\vb\biblio.mdb")
         Set ds = db.OpenRecordset("Authors")
      End Sub
   
      Private Sub Form_Unload()
         ds.Close
         db.Close
      End Sub
                           

6. Change the Interval property of the Timer control to 3000 (3 seconds).

7. Insert the following code in the Timer1_Timer event procedure:

      Private Sub Timer1_Timer()
         Dim s As String
         s = Time$ + " / " + ds("Author")
         Label1.Caption = s
      End Sub
                           

8. On the Run menu, click start (ALT, R, S), or press the F5 key to run the program.

9. Start another copy of Visual Basic, and load and run the VisData sample application located in \Vb\Samples\Visdata. Open the same Biblio.mdb database referenced in your code. Open the Authors table, make a change to the Author field of the first record, and update the database. With Visual Basic 3.0, the change will be visible immediately in the running application, but with Visual Basic 4.0 no change will be evident.
   
   To correct this behavior, add the following line of code to the Timer1_Timer event procedure:

         DBEngine.Idle dbFreeLocks
                           

NOTE: The Biblio.mdb database that ships with Visual Basic 4.0 is saved as a Microsoft Jet 2.0 database. You can use VisData to convert this to a Microsoft Jet 3.0 database. If the above example is followed using Visual Basic 4.0 and a Microsoft Jet 3.0 database, no call to DBEngine.Idle is necessary.

Additional query words: 4.00 vb4win vb4all

Keywords: kbprb KB137023

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