PRB: VFP Crashes When Working With Top-Level & Child Forms

• Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a

SYMPTOMS

Running a Top-Level form and one or more child forms within it, and then closing the Top-Level form, may produce error messages or phantom copies of the top-level form. Following these problems the Project Manager may produce Access Violations when you try to Build/Rebuild a project.

RESOLUTION

The above problems occur in the development version of Visual FoxPro. If the Top-Level form is being created for use as an EXE and the EXE is designed to end when the Top-Level form is closed, there should be no problems using the Top-Level form with its child forms.

STATUS

Microsoft is researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

The following symptoms may appear when developing a project containing a Top-Level form that has child forms contained within it. Running a Top- Level form and one or more child forms within it and then closing the Top- Level form, may cause the following symptoms in Visual FoxPro:

1. The error message "FORMS is not an object." This happens while closing the Top-Level form when child forms are open within it.

2. "Phantom" copies of the Top-Level form remaining on the Windows Taskbar for each time the Top-Level form was run and closed with a child form within. They can be activated and the form's border and title bar will show but they cannot be moved, minimized or maximized, or closed. They are also transparent, whatever application is behind them can be seen but not accessed through the form. Use the Windows Taskbar or click on the visible portion of the application outside of the "phantom" Top-Level form to activate the desired application. These "phantom" forms only go away if Visual FoxPro is shut down.

3. Choosing the Build button in the Project Manager to build or rebuild anything will cause Visual FoxPro to crash with an Access Violation in Windows NT or to end with the "This program has performed an illegal operation and will be shut down" error message in Windows 95. Using the command line BUILD commands(BUILD PROJECT, BUILD EXE, BUILD APP or BUILD DLL) will also cause the errors. This only happens if there is a "phantom" form as described in #2 above.

   In Windows NT 4.0 with Service Pack 3, the exact error message with addresses is this:

         An application error has occurred and an application error log is
         being generated.
                          vfp.exe
         Exception: access violation (0xc0000005), Address: 0x004025a0
   
      In Windows 95, the details of the error message is this:
   
         VFP caused an invalid page fault in
         module VFP.EXE at 0137:00402960.
         Registers: <register info not repeated in this article>
   
   

Steps to Reproduce Behavior

To reproduce this problem, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q175625
   TITLE     : FILE: Use Topclose.exe to Close Child Forms Of Top-Level
               Forms

NOTE: The following information assumes that the sample files from the above mentioned KB article has been downloaded and explored.

Just run the Almost.app and follow the instructions on the Top-Level form to see the "phantom" form(s) appear. After there is at least one "phantom" form, try rebuilding the Almost.pjx and Visual FoxPro should crash.

To get the error message "FORMS is not an object", make the following modifications to the QueryUnload method of thE Almost.scx form in the Almost.pjx project:

1. Replace the DO WHILE loop with a FOR...ENDFOR loop. To do this, remark out the following line of code:

         DO WHILE _Screen.ActiveForm.Caption != "Good Top-Level Form"
   

   and replace it with the following two lines of code:

            FOR x=1 TO xx
            IF _SCREEN.FORMS(x).CAPTION != "Good Top-Level Form"
   
      The variable xx is already setup at the beginning of the QueryUnload
      code to contain _Screen.FormCount. At the end of the DO WHILE loop,
      remark out the following line of code:
   
         ENDDO
   
      and replace it with the following two lines of code:
   
            ENDIF
            ENDFOR
   
   

2. Save the form and rebuild the application.

3. Run the Almost.app application and open at least one child form and then close the Top-Level form. The error message "FORMS is not an object" should appear before all the forms are closed.

Keywords          : FxprgGeneral FxtoolProjman vfoxwin kberrmsg
Version           : WINDOWS:5.0,5.0a
Platform          : WINDOWS
Issue type        : kbprb
Solution Type     : kbpending kbworkaround