I have an application that auto logs a user off of the program. I have seen an issue when the user has a Message Box open when the auto-logoff routine fires; "Can't show a non-modal form when a modal form is displayed".

So, what I did was write a routine that check's the current thread for any open message boxes and then use a SendMessage API to close the message box. The message box is closed successfully, but the error still occurs. If I remove the message box from the code then it works fine. Need HELP here!! I have even tried a DoEvents loop after the call to "CloseMessageBox" but the error still occurs, any ideas?!

Here is the code to test it: (can't run from VB as the timers do not fire when a message box is open, so it must be compiled into an exe first)

VB Code:
  1. '***IN A FORM

  2.  
  3. Private Sub Form_Activate()

  4.     MsgBox "Test Message"

  5. End Sub

  6.  
  7. Private Sub Form_Load()

  8.     Timer1.Interval = 1000

  9. End Sub

  10.  
  11. Private Sub Timer1_Timer()

  12.  
  13.     Dim lProcessID As Long

  14.     Dim lID As Long

  15.     

  16.     Timer1.Interval = 0

  17.     

  18.     'get the process ID for prosper

  19.     lProcessID = GetWindowThreadProcessId(Me.hWnd, lID)

  20.     

  21.     'close any open message boxes

  22.     CloseMessageBox lProcessID

  23.     

  24.     Form2.Show

  25.  
  26. End Sub

  27.  
  28. '***IN A MODULE

  29.  
  30. Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal lWindowHwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long

  31. Private Declare Function EnumChildWindows Lib "user32" (ByVal hWndParent As Long, ByVal lpEnumFunc As Long, ByVal lParam As Long) As Long

  32. Private Declare Function GetClassName Lib "user32" Alias "GetClassNameA" (ByVal lWindowHwnd As Long, ByVal lpClassName As String, ByVal nMaxCount As Long) As Long

  33. Private Declare Function EnumThreadWindows Lib "user32" (ByVal dwThreadId As Long, ByVal lpfn As Long, ByVal lParam As Long) As Long

  34.  
  35. 'used for message box closing

  36. Public Declare Function GetWindowThreadProcessId Lib "user32" (ByVal lWindowHwnd As Long, lpdwProcessId As Long) As Long

  37.  
  38. Private Const MSGBOX_CLASS_ID = "#32770"

  39. Private Const WM_GETTEXT = &HD

  40. Private Const WM_CLOSE = &H10

  41. Private Const BUFFER_SIZE As Integer = 255

  42.  
  43. Private lMsgBoxHwnd As Long

  44. Private sMsgText As String

  45. Private bMsgBox As Boolean

  46.  
  47. Public Sub CloseMessageBox(ByVal lOwnerProcess As Long)

  48.     

  49.     On Error GoTo ErrorHandler:

  50.     

  51.     Dim lProcessID As Long

  52.     Dim lID As Long

  53.     

  54.     'reset the handle

  55.     lMsgBoxHwnd = 0

  56.     

  57.     'enumerates top-level windows

  58.     Call EnumThreadWindows(lOwnerProcess, AddressOf EnumWindowProc, 0&)

  59.     

  60.     'if a valid message box handle was found

  61.     If (lMsgBoxHwnd <> 0) Then

  62.         

  63.         'send a message to close the message box

  64.         SendMessage lMsgBoxHwnd, WM_CLOSE, 0&, 0&

  65.         

  66.     End If

  67.     

  68.     Exit Sub

  69.  
  70. ErrorHandler:

  71.  
  72. End Sub

  73.  
  74. Private Function EnumWindowProc(ByVal lWindowHwnd As Long, ByVal lParam As Long) As Long

  75.     

  76.     On Error GoTo ErrorHandler:

  77.     

  78.     Dim sClassName As String

  79.     

  80.     'create a buffer

  81.     sClassName = Space(BUFFER_SIZE)

  82.     

  83.     'truncate the class name buffer

  84.     sClassName = Left(sClassName, GetClassName(lWindowHwnd, ByVal sClassName, BUFFER_SIZE))

  85.     

  86.     'if a dialog class was found

  87.     If StrComp(Left(sClassName, Len(MSGBOX_CLASS_ID)), MSGBOX_CLASS_ID, vbTextCompare) = 0 Then

  88.     

  89.         'verify it's a standard message box style dialog

  90.         If IsMsgBoxDialog(lWindowHwnd) Then

  91.             lMsgBoxHwnd = lWindowHwnd

  92.             lWindowHwnd = 0

  93.         End If

  94.         

  95.     End If

  96.     

  97.     'return the window handle

  98.     EnumWindowProc = lWindowHwnd

  99.  
  100.     Exit Function

  101.  
  102. ErrorHandler:

  103.  
  104. End Function

  105.  
  106. Private Function IsMsgBoxProc(ByVal lWindowHwnd As Long, ByVal lParam As Long) As Long

  107.     

  108.     On Error GoTo ErrorHandler:

  109.  
  110.     Dim sClass As String

  111.     Dim sCaption As String

  112.     

  113.     'create a buffer

  114.     sClass = Space(BUFFER_SIZE)

  115.     

  116.     'extract the class name of this child window

  117.     sClass = Left(sClass, GetClassName(lWindowHwnd, ByVal sClass, BUFFER_SIZE))

  118.     

  119.     'if a button class

  120.     If InStr(LCase(sClass), "button") Then

  121.         

  122.         'create a buffer

  123.         sCaption = Space(BUFFER_SIZE)

  124.         

  125.         'see if it's caption qualifies as a Msgbox button caption

  126.         sCaption = Left(sCaption, SendMessage(lWindowHwnd, WM_GETTEXT, BUFFER_SIZE, ByVal sCaption))

  127.         

  128.         'is it a valid message box

  129.         If InStr(",OK,ABORT,RETRY,YES,NO,CANCEL,IGNORE,", "," & Replace(UCase(sCaption), "&", "") & ",") Then

  130.             lWindowHwnd = 0

  131.             bMsgBox = True

  132.         End If

  133.         

  134.     End If

  135.     

  136.     'return the handle

  137.     IsMsgBoxProc = lWindowHwnd

  138.  
  139.     Exit Function

  140.  
  141. ErrorHandler:

  142.  
  143. End Function

  144.  
  145. Private Function IsMsgBoxDialog(ByVal lWindowHwnd As Long) As Boolean

  146.     

  147.     On Error Resume Next

  148.     

  149.     'reset the flag

  150.     bMsgBox = False

  151.     

  152.     'enumerate child windows

  153.     Call EnumChildWindows(lWindowHwnd, AddressOf IsMsgBoxProc, 0&)

  154.     

  155.     'return the success value

  156.     IsMsgBoxDialog = bMsgBox

  157.     

  158. End Function