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Preventing any Msgbox's from being display (and capturing the message)

Preventing any Msgbox's from being display (and capturing the message)

Occasionally it is useful to stop any Msgbox's from being displayed in your application. The following code allows you to turn off all Msgbox's in your application and capture their contents.


Option Explicit
Private Declare Function GetForegroundWindow Lib "user32" () As Long
Private Declare Function GetClassName Lib "user32" Alias "GetClassNameA" (ByVal hwnd As Long, ByVal lpClassName As String, ByVal nMaxCount As Long) As Long
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Integer, ByVal lParam As Any) As Long
Private Declare Function GetWindowText Lib "user32" Alias "GetWindowTextA" (ByVal hwnd As Long, ByVal lpString As String, ByVal cch As Long) As Long
Private Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal hWnd1 As Long, ByVal hWnd2 As Long, ByVal lpsz1 As String, ByVal lpsz2 As String) As Long
Private Declare Function GetCurrentThreadId Lib "kernel32" () As Long
Private Declare Function SetWindowsHookEx Lib "user32" Alias "SetWindowsHookExA" (ByVal idHook As Long, ByVal lpfn As Long, ByVal hmod As Long, ByVal dwThreadId As Long) As Long
Private Declare Function UnhookWindowsHookEx Lib "user32" (ByVal zlhHook As Long) As Long



'Purpose     :  To capture any Msgbox's shown on this thread
'Inputs      :  bEnabled            If True switches on msgbox capturing, else switches off.
'Outputs     :  N/A (see the function zCaptureMsgbox where the contents of the msgbox are printed)
'Notes       :  PLACE IN A MODULE. Can only be used within the application process.


Function MsgboxCapture(bEnabled As Boolean)
    Const WH_CBT = 5              'Respond to certain system actions, making it possible to develop computer-based training (CBT) for applications (WH_CBT).
    Dim lThread As Long, lhInst As Long
    Static slhHook As Long
    
    If bEnabled = False Then
        lThread = GetCurrentThreadId
        slhHook = SetWindowsHookEx(WH_CBT, AddressOf zCaptureMsgbox, App.hInstance, lThread)
    Else
        'Release the CBT hook
        UnhookWindowsHookEx slhHook
    End If
End Function

'Private call back function used to capture and close and MsgBox's
'Notes       :  PLACE IN A MODULE
Private Function zCaptureMsgbox(ByVal lMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
    Const WM_CLOSE = &H10&, HCBT_ACTIVATE = 5
    Const clMaxText As Long = 255
    Const WH_MSGFILTER = (-1)
    
    Dim sClassName As String * clMaxText, sMsgboxText As String * clMaxText
    Dim lHwndWindow As Long, lNumChars As Long, lHwndText As Long
    
    If lMsg = 6 Then
        lHwndWindow = GetForegroundWindow
        lNumChars = clMaxText
        lNumChars = GetClassName(lHwndWindow, sClassName, lNumChars)
        If UCase(Left$(sClassName, lNumChars)) = "#32770" Then
            'The active window is a Msgbox, get the message and close it
            lHwndText = FindWindowEx(lHwndWindow, 0&, "Static", vbNullString)
            lNumChars = clMaxText
            lNumChars = GetWindowText(lHwndText, sMsgboxText, lNumChars)
            Debug.Print "Message box captured: " & Left$(sMsgboxText, lNumChars)
            Call SendMessage(lHwndWindow, WM_CLOSE, 0&, 0&)
        End If
    End If
    zCaptureMsgbox = 0
End Function


'Demonstration code (PLACE IN A FORM)
Private Sub Command1_Click()
    MsgboxCapture False
    MsgBox "Hello Doesn't show"
    MsgboxCapture True
    MsgBox "Hello Does show"
End Sub