FIX: Combo Box Behaves Erratically with Timer Control

• Microsoft Visual FoxPro for Windows, version 5.0

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.

   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 : kbprg kbVFp kbVFp500afix kbVFp500bug FxprgGeneral
Version : WINDOWS:5.0
Platform : WINDOWS
Issue type : kbbug