BUG: Show Event Calls Refresh Despite NODEFAULT in Subclass

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

SYMPTOMS

When an instance of a form subclass has its Show() method called, if its Refresh() method calls the parentclass Refresh(), a NODEFAULT in the subclass Refresh() will be ignored and the Refresh() method for each control on the form will be called twice.

WORKAROUND

Conditionally issue a NODEFAULT in the parent class Refresh() method.

STATUS

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

MORE INFORMATION

Normally, this behavior will not create much of a problem because it will result in the Refresh() for each control getting called twice by the Show() only if the conditions in SYMPTOMS section are met. In the rare case that this actually causes a problem, the steps described below in Demonstration of Workaround can be utilized.

Steps to Reproduce Problem

1. Run the following code from a program (.PRG) file:

   * Start of code example * CLEAR oForm = CREATE("FormChild") ACTIVATE SCREEN ?'Following lines from Show()' oForm.SHOW() ACTIVATE SCREEN ? '' ?'Following lines from Refresh()' oForm.REFRESH() ACTIVATE SCREEN ? '' ?'Following lines from Show()' oForm.SHOW()

   DEFINE CLASS FormChild AS FormParent

         AUTOCENTER = .T.
   

         ADD OBJECT text1 AS TEXTBOX
   

         PROCEDURE text1.REFRESH
            ACTIVATE SCREEN
            ?'In Textbox Refresh'
         ENDPROC
   
         PROCEDURE REFRESH()
            ACTIVATE SCREEN
            ?'In FormChild Refresh'
            DODEFAULT()
            NODEFAULT
         ENDPROC
      ENDDEFINE
   
      DEFINE CLASS FormParent AS FORM
         PROCEDURE REFRESH()
            ACTIVATE SCREEN
            ?'In FormParent Refresh'
         ENDPROC
      ENDDEFINE
      *
      * End of code example
   
   

2. In spite of the NODEFAULT in the Refresh() of the FormChild class, when the Show() method is called, the Refresh() of Text1 will get called twice: once by the FormChild Refresh() and once by the FormParent Refresh(). This does not occur if the Refresh() is called directly, only if the Refresh() is called implicitly through the Show() method.

Demonstration of Workaround

Rationale - Set a flag in the Show() that causes the parent class Refresh() to conditionally execute a NODEFAULT and not carry out its default behavior of calling the refresh of all controls on the form.