Q167193: FIX: Buffering Lost when txtbtns Exit Clicked

Article: Q167193
Product(s): Microsoft FoxPro
Version(s): 3.0b 5.0 5.0a
Operating System(s): 
Keyword(s): kbprogramming kbtool kbvfp kbvfp300 kbvfp500 kbvfp500a kbvfp600fix
Last Modified: 24-MAR-2000

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 3.0b, 5.0, 5.0a 
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SYMPTOMS
========

When an application has more than one form, and buffer mode is other than 1
(unbuffered), the buffering will be lost under certain circumstances. This
happens when one or more of the forms uses the DataEnvironment, uses the txtbtns
class of the Wizstyle.vcx class library, and the Exit button is clicked.

In Visual FoxPro for Windows versions 3.0 and 3.0b an error message appears when
the Revert button is clicked on the surviving form. The message says "Function
Requires Row or Table Buffering Mode."

In Visual FoxPro for Windows versions 5.0 and 5.0a there is no message, but the
"Revert" button becomes inoperative--a sign that there is nothing in the buffer
to revert.

CAUSE
=====

Code in the DESTROY method of the txtbtns class resets buffermode to '1' when
the Exit button is clicked. This code is by design to prevent OLE servers from
updating general field data during the destroy event. The form is to be
released, so no more data changes should be posted to tables involved with that
form.

RESOLUTION
==========

If the application does not have tables with general fields that are subject to
updating whenever the table is open, the line in the DESTROY method of the
txtbtns class that sets buffering to '1' may be commented out.

The line is approximately 30 lines into the txtbtns.DESTROY method. It is as
follows:

     = CursorSetProp("Buffering",1,.ALIAS)  &&optimistic table buffering

The comment on that line is incorrect.

This change is not supported by Microsoft, and the results of any modification to
any of the code in the Wizstyle.vcx library are uncertain because of the
numerous dependencies between functions, values, and event methods within the
code of those classes. The user makes such modifications at her or his own risk.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This has been corrected in Visual FoxPro 6.0.

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

1. Start a new project called Onetwo.pjx. Add a new form named 'one' to the
  project. Set the name property to "one" (without the quotes).

2. Set the Buffermode property of form one to "2 - optimistic."

3. Open the DataEnvironment for form one and add the Customer table from
  \Samples\Data.

4. Drag the cust_id, company, and contact fields to the form.

5. Add the Wizstyle.vcx class library from the VFP\Wizards folder to the Forms
  Designer's toolbar.

6. From the Wizstyle toolbar select txtbtns and add it to the bottom of form
  one.

7. Add a single command button captioned "Form Two" to form one. In its Click
  method place the command:

        DO FORM two NAME two LINKED

8. In the LOAD method of form 'one' add the declaration:

        PUBLIC two

  to declare a variable named "two."

9. Save the definition of form one into the VFP root directory.

10. Add a second form to the project. Name this form "two." Set its Name
  property to "two" (without the quotes).

11. Set the Buffermode property of form two to "2 - optimistic."

12. Open the DataEnvironment of form two. Add the customer and the orders table
  to the DataEnvironment. A parent-child relationship should appear between
  the two tables.

13. Drag the Cust_ID and Company fields to the form. Add the child (orders)
  table to the form as a grid. In Visual FoxPro version 5.0 the default
  Control Source for the grid columns are mapped from the fields of the table.
  In Visual FoxPro version 3.x, you need to set a columncount, and map the
  control source of each column.

14. Add the txtbtns class to the bottom of form two.

15. Save form two as Two.scx in the Visual FoxPro root directory.

16. In the debugger (for Visual FoxPro 5.0) or the Debug window (for Visual
  FoxPro 3.0), add a watch on 'Cursorgetprop("Buffering")' and set a
  breakpoint on that value (it will break when the value changes). To set the
  breakpoint double-click on the gray rectangle at the left of the 'Name'
  value in the Visual FoxPro 5 Watch window, or on the gray bar between the
  left and right panes of the Visual FoxPro 3 Debug window.

17. Run form one. Click the Edit button, then click the Form Two command button.
  Form two appears.

18. Click the Exit button on form two.

In the Debugger the running code will BREAK, when the value of
Cursorgetprop("Buffering") changes from 3 to 1. In the Trace window the code
shows an arrow at the ENDIF statement just after the offending command:

     =cursorsetprop("buffering",1,.ALIAS)  &&optimistic table buffering

Visual FoxPro 5.0 and 5.0a disable the Revert button in form one, although the
Caption is enabled until it is clicked.

Visual FoxPro 3.0 and 3.0b show the error message "Function Requires Row or Table
Buffering Mode" when 'Revert' is clicked on form one.

Additional query words:

======================================================================
Keywords          : kbprogramming kbtool kbvfp kbvfp300 kbvfp500 kbvfp500a kbvfp600fix 
Technology        : kbVFPsearch kbAudDeveloper kbVFP300b kbVFP500 kbVFP500a
Version           : 3.0b 5.0 5.0a
Issue type        : kbbug kbprb
Solution Type     : kbfix

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