Q161184: FIX: Combo Box Behaves Erratically with Timer Control

Article: Q161184
Product(s): Microsoft FoxPro
Version(s): WINDOWS:5.0
Operating System(s): 
Keyword(s): kbprogramming kbvfp kbvfp500aFIX kbvfp500bugkbbuglist kbfixlist
Last Modified: 11-DEC-1999

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 5.0 
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SYMPTOMS
========

Using a Timer Control and a combo box simultaneously may produce erratic
results. Under some circumstances, the combo box may not reflect the last item
chosen from its list. However, many times it may act properly. Furthermore, if a
check box is present, the check box may become automatically unchecked when
certain selections are made from the combo box list.

RESOLUTION
==========

The example below contains two procedures, PROCEDURE Combo1.Valid and PROCEDURE
Check1.MouseDown, which are included in the code as comments. By removing the
asterisks, the two procedures fix the problems. The first procedure,
Combo1.Valid, allows the selection of any item in the combo's list. The second
procedure, Check1.MouseDown, prevents the check box from becoming unchecked by
selections made within the combo box.

STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft products listed at
the beginning of this article. This problem has been fixed in Visual FoxPro
5.0a.

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

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

1. Place the following code in a program and run it:

     PUBLIC oform1
     oForm1=CREATEOBJECT("Form1")
     oForm1.Show

     DEFINE CLASS form1 AS form
        Height = 297
        Width = 579
        AutoCenter = .T.
        Caption = "ComboBox/Timer Example"
        Name = "Form1"

     ADD OBJECT timer1 AS timer WITH ;
        Top = 270, ;
        Left = 278, ;
        Height = 23, ;
        Width = 23, ;
        Interval = 1000, ;
        Name = "Timer1"

     ADD OBJECT combo1 AS combobox WITH ;
        RowSourceType = 1, ;
        RowSource = "Test 1,Test 2,Test 3,Test 4", ;
        Height = 24, ;
        Left = 239, ;
        Style = 2, ;
        Top = 180, ;
        Width = 100, ;
        Name = "Combo1"

     ADD OBJECT check1 AS checkbox WITH ;
        Top = 239, ;
        Left = 239, ;
        Height = 17, ;
        Width = 100, ;
        Caption = "Timer Enabled", ;
        Value = .T., ;
        Name = "Check1"

     ADD OBJECT edit1 AS editbox WITH ;
        FontBold = .T., ;
        FontSize = 8, ;
        BackStyle = 0, ;
        BorderStyle = 0, ;
        Height = 165, ;
        Left = 6, ;
        ReadOnly = .T., ;
        ScrollBars = 0, ;
        SpecialEffect = 1, ;
        TabStop = .F., ;
        Top = 5, ;
        Width = 564, ;
        Name = "Edit1"

      PROCEDURE check1.Refresh
        ThisForm.Timer1.Enabled=This.Value
      ENDPROC

      PROCEDURE check1.Click
         This.Refresh
      ENDPROC

     PROCEDURE edit1.Init
        This.Value="A Timer is running when Timer Enabled is checked." ;
        +CHR(13)+CHR(13)+ ;
        "Whenever a timer is running (Enabled=.T., Interval>0, lower values";
        +CHR(13)+ ;
        "make it more likely to show problem), both user defined and system";
        +CHR(13)+ ;
        "(VFP) dropdown list ComboBoxes (Style=2) don't work.";
        + CHR(13) +CHR(13)+ ;
        "When the Timer is on, select Test 1 or Test 4 and it usually";
        +CHR(13)+ ;
        "doesn't select."+CHR(13)+CHR(13)+ ;
        "With the Timer control on, select Test 3 twice in a row and the" ;
        +CHR(13)+ ;
        "checkbox is often unchecked automatically."+CHR(13)+CHR(13)+ ;
        "Turn off the Timer and the ComboBoxes work properly."+CHR(13)
     ENDPROC

     ****The following code fixes the problems*****

     *PROCEDURE Combo1.Valid
     *This.Refresh
     *ENDPROC

     *PROCEDURE  Check1.mousedown
      *  LPARAMETERS nButton, nShift, nXCoord, nYCoord
       * WAIT "" TIME .01
     *ENDPROC

     ENDDEFINE

2. With the Timer enabled, the "Timer Enabled" check box is selected by default,
  make several selections from the combo box. Select the "Test 3" item and
  notice the check box becomes unchecked.

3. Clear the "Timer Enabled" check box and make selections from the combo box.
  The object acts normally.

The following code may be used in lieu of the above workaround:

     PROCEDURE Combo1.mousedown
     LPARAMETERS nButton, nShift, nXCoord, nYCoord
       thisform.timer1.enabled= .f.
     ENDPROC

     PROCEDURE Combo1.InteractiveChangeEvent
     LPARAMETERS nButton, nShift, nXCoord, nYCoord
       thisform.timer1.enabled= .t.
     ENDPROC

Additional query words:

======================================================================
Keywords          : kbprogramming kbvfp kbvfp500aFIX kbvfp500bug kbbuglist kbfixlist
Technology        : kbVFPsearch kbAudDeveloper kbVFP500
Version           : WINDOWS:5.0
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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