Q187274: BUG: Referencing This.Value in Editbox Refresh Causes Error

Article: Q187274
Product(s): Microsoft FoxPro
Version(s): WINDOWS:3.0,3.0b,5.0,5.0a
Operating System(s): 
Keyword(s): 
Last Modified: 11-AUG-1999

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The information in this article applies to:

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

Referencing This.Value property within an Editbox object's Refresh event causes
a memory protection error in Visual FoxPro. Under Windows 95, an application
error appears indicating an invalid page fault occurred. On Windows NT 4.0, a
Dr. Watson for Windows NT dialog appears stating an application error occurred
and that Visual FoxPro caused an exception violation at a given memory address.

RESOLUTION
==========

Call the DODefault() method of the Editbox before the This.Value command in the
Refresh event. In the code example below, change the Refresh event code to read
as follows:

     PROCEDURE Refresh
        IF THISFORM.chkRef.Value
           DODEFAULT()
           WAIT WINDOW THIS.Value NOWAIT
        ENDIF
        RETURN
     ENDPROC

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. We are researching this bug and will post new
information here in the Microsoft Knowledge Base as it becomes available.

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

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

1. Create a program that contains the following code and run the program:

        CLOSE ALL

        CREATE CURSOR Test (Field1 M, Field2 C(12), Key N(2))
        INSERT INTO Test (Field1, Field2, Key) VALUES ;
           ("This is some text.","More", 1)
        INSERT INTO Test (Field1, Field2, Key) VALUES ("", "Other", 2)
        CREATE DATABASE Test
        CREATE SQL VIEW "TestView" AS SELECT * FROM Test WHERE Key = ?m.Key

        Key = 1
        USE TestView

        PUBLIC ox
        ox=CREATEOBJECT("frmTest")
        ox.Visible = .T.

        RETURN

        DEFINE CLASS FrmTest AS FORM
           ADD OBJECT edtField1 AS edtField1
           ADD OBJECT txtField2 AS txtField2
           ADD OBJECT cmdButton AS cmdButton
           ADD OBJECT chkRef AS chkRef

        ENDDEFINE

        DEFINE CLASS chkRef AS CheckBox
           Top = 190
           Width = 200
           Left = 20
           Caption = "Refer to the Value in the Refresh"
           Value = .F.
        ENDDEFINE

        DEFINE CLASS cmdButton AS CommandButton
           Top = 20
           Height = 30
           Left = 200
           Caption = "Another Record"
           PROCEDURE Click
              Key = TestView.Key + 1
              IF m.Key > RECCOUNT("Test")
                 Key = 1
              ENDIF
              =REQUERY("TestView")
              THISFORM.Refresh()
              RETURN
          ENDPROC

        ENDDEFINE

        DEFINE CLASS txtField2 AS TextBox
           Top = 20
           Height = 30
           Left = 20
           ControlSource = "TestView.Field2"
        ENDDEFINE

        DEFINE CLASS edtField1 AS EditBox
           Top = 100
           Left = 20
           ControlSource = "TestView.Field1"

           PROCEDURE Refresh
              IF THISFORM.chkRef.Value
                 WAIT WINDOW THIS.Value NOWAIT
              ENDIF
              RETURN
           ENDPROC

        ENDDEFINE

2. When the form appears, click the check box and press the command button. The
  error message appears.

Additional query words: kbDSupport KBDSE crash hang gpf kbVFp500bug

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Keywords          :  
Technology        : kbVFPsearch kbAudDeveloper kbVFP300 kbVFP300b kbVFP500 kbVFP500a
Version           : WINDOWS:3.0,3.0b,5.0,5.0a
Issue type        : kbbug
Solution Type     : kbpending

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