DOCUMENT:Q161184  11-DEC-1999  [foxpro]
TITLE   :FIX: Combo Box Behaves Erratically with Timer Control
PRODUCT :Microsoft FoxPro
PROD/VER:WINDOWS:5.0
OPER/SYS:
KEYWORDS:kbprogramming kbvfp kbvfp500aFIX kbvfp500bugkbbuglist kbfixlist

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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:

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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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