'needed public for the Timer event
Public hwndMsgBox As Long

'custom user-defined type to pass
'info between procedures - easier than
'passing a long list of variables.
'Needed public for the Timer event
Public Type CUSTOM_MSG_PARAMS
   hOwnerThread         As Long
   hOwnerWindow         As Long
   dwStyle              As Long
   bUseTimer            As Boolean
   dwTimerDuration      As Long
   dwTimerInterval      As Long
   dwTimerExpireButton  As Long
   dwTimerCountDown     As Long
   sTitle               As String
   sPrompt              As String
End Type

Public cmp As CUSTOM_MSG_PARAMS

'Windows-defined uType parameters
Public Const MB_ICONINFORMATION As Long = &H40&
Private Const MB_ABORTRETRYIGNORE As Long = &H2&
Private Const MB_TASKMODAL As Long = &H2000&

'Windows-defined MessageBox return values
Private Const IDOK = 1
Private Const IDCANCEL = 2
Private Const IDABORT = 3
Private Const IDRETRY = 4
Private Const IDIGNORE = 5
Private Const IDYES = 6
Private Const IDNO = 7

'This section contains user-defined constants
'to represent the buttons/actions we are
'creating, based on the existing MessageBox
'constants. Doing this makes the code in
'the calling procedures more readable, since
'the messages match the buttons we're creating.
Public Const MB_SELECTBEGINSKIP As Long = MB_ABORTRETRYIGNORE
Public Const IDSELECT = IDABORT
Public Const IDBEGIN = IDRETRY
Public Const IDSKIP = IDIGNORE
Public Const IDPROMPT = &HFFFF&

'misc API constants
Private Const WH_CBT = 5
Private Const GWL_HINSTANCE = (-6)
Private Const HCBT_ACTIVATE = 5
Public Const WM_LBUTTONDOWN = &H201
Public Const WM_LBUTTONUP = &H202

'UDT for passing data through the hook
Private Type MSGBOX_HOOK_PARAMS
   hwndOwner   As Long
   hHook       As Long
End Type

'need this declared at module level as
'it is used in the call and the hook proc
Private MHP As MSGBOX_HOOK_PARAMS

Private Declare Function GetCurrentThreadId Lib "kernel32" () As Long

Public Declare Function GetDesktopWindow Lib "user32" () As Long

Private Declare Function GetWindowLong Lib "user32" _
   Alias "GetWindowLongA" _
  (ByVal hwnd As Long, _
   ByVal nIndex As Long) As Long

Public Declare Function GetDlgItem Lib "user32" _
  (ByVal hDlg As Long, _
   ByVal nIDDlgItem As Long) As Long
   
Private Declare Function MessageBox Lib "user32" _
   Alias "MessageBoxA" _
  (ByVal hwnd As Long, _
   ByVal lpText As String, _
   ByVal lpCaption As String, _
   ByVal wType As Long) As Long
   
Public Declare Function PostMessage Lib "user32" _
   Alias "PostMessageA" _
  (ByVal hwnd As Long, _
   ByVal wMsg As Long, _
   ByVal wParam As Long, lParam As Long) As Long
      
Public Declare Function PutFocus Lib "user32" _
   Alias "SetFocus" _
  (ByVal hwnd As Long) As Long
  
Public Declare Function SetDlgItemText Lib "user32" _
   Alias "SetDlgItemTextA" _
  (ByVal hDlg As Long, _
   ByVal nIDDlgItem As Long, _
   ByVal lpString As String) 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 SetWindowText Lib "user32" _
   Alias "SetWindowTextA" _
  (ByVal hwnd As Long, _
   ByVal lpString As String) As Long

Private Declare Function UnhookWindowsHookEx Lib "user32" _
   (ByVal hHook As Long) As Long
    


Public Function MsgBoxHookProc(ByVal uMsg As Long, _
                               ByVal wParam As Long, _
                               ByVal lParam As Long) As Long
      
  'When the message box is about to be shown,
  'we'll change the titlebar text, prompt message
  'and button captions
   If uMsg = HCBT_ACTIVATE Then
   
     'in a HCBT_ACTIVATE message, wParam holds
     'the handle to the messagebox - save that
     'for the timer event
      hwndMsgBox = wParam
              
     'the ID's of the buttons on the message box
     'correspond exactly to the values they return,
     'so the same values can be used to identify
     'specific buttons in a SetDlgItemText call.
      SetDlgItemText wParam, IDSELECT, "Select.."
      SetDlgItemText wParam, IDBEGIN, "Begin"
      SetDlgItemText wParam, IDSKIP, "Skip"
      
     'we're done with the dialog, so release the hook
      UnhookWindowsHookEx MHP.hHook
               
   End If
   
  'return False to let normal processing continue
   MsgBoxHookProc = False

End Function


Public Function TimedMessageBoxH(cmp As CUSTOM_MSG_PARAMS) As Long

   Dim hInstance As Long
   Dim hThreadId As Long
   
  'Set up the hook
   hInstance = GetWindowLong(cmp.hOwnerThread, GWL_HINSTANCE)
   hThreadId = GetCurrentThreadId()

  'set up the MSGBOX_HOOK_PARAMS values
  'By specifying a Windows hook as one
  'of the params, we can intercept messages
  'sent by Windows and thereby manipulate
  'the dialog
   With MHP
      .hwndOwner = cmp.hOwnerWindow
      .hHook = SetWindowsHookEx(WH_CBT, _
                                AddressOf MsgBoxHookProc, _
                                hInstance, hThreadId)
   End With
   
  '(re)set the countdown value to 0
   cmp.dwTimerCountDown = 0
   
  'if bUseTimer, enable the timer. Because the
  'MessageBox API acts just as the MsgBox function
  'does (that is, creates a modal dialog), control
  'won't return to the next line until the dialog
  'is closed. This necessitates our starting the
  'timer before making the call.
  '
  'However, timer events will execute once the
  'modal dialog is shown, allowing us to use the
  'timer to dynamically modify the on-screen message!
   With Form1.Timer1
      .Interval = cmp.dwTimerInterval
      .Enabled = cmp.bUseTimer
   End With

  'call the MessageBox API and return the
  'value as the result of the function
   TimedMessageBoxH = MessageBox(cmp.hOwnerWindow, _
                                 cmp.sPrompt, _
                                 cmp.sTitle, _
                                 cmp.dwStyle)

  'in case the timer event didn't
  'suspend the timer, do it now
   Form1.Timer1.Enabled = False

End Function

Option Explicit

Private Sub Command1_Click()
  
  'Display wrapper message box,
  'passing the CUSTOM_MSG_PARAMS
  'struct as the parameter.
   With cmp
      .sTitle = "VBnet Timed MessageBox Hook Demo"
      .sPrompt = "To start searching C: immediately, select Begin." & vbCrLf & _
                 "To select a different drive, press Select." & vbCrLf & vbCrLf & _
                 "Automatic searching of C: will begin in 10 seconds." & Space$(20)
      .dwStyle = MB_SELECTBEGINSKIP Or MB_ICONINFORMATION
      .bUseTimer = True               'if True the Timer will update once per dwTimerInterval
      .dwTimerDuration = 10           'time to wait seconds
      .dwTimerInterval = 1000         'countdown interval in milliseconds
      .dwTimerExpireButton = IDBEGIN  'message to return if timeout occurs
      .dwTimerCountDown = 0           '(re)set to 0
      .hOwnerThread = Me.hwnd         'handle of form owning the thread on which
                                      'execution is proceeding.
                                      'The thread owner is always the calling form.
      .hOwnerWindow = Me.hwnd         'who owns the dialog (me.hwnd or desktop).
                                      'GetDesktopWindow allows user-interaction
                                      'with the form while the dialog is displayed.
                                      'This may not be desirable, so set accordingly.
   End With

   Select Case TimedMessageBoxH(cmp)
      Case IDSELECT: Text1.Text = "Select button pressed before timeout"
      Case IDBEGIN:  Text1.Text = "Begin button pressed or message timed out"
      Case IDSKIP:   Text1.Text = "Skip button pressed before timeout"
   End Select
     
End Sub

Private Sub Timer1_Timer()

   Dim hWndTargetBtn As Long
   
   If hwndMsgBox <> 0 Then
   
     'increment the counter
      cmp.dwTimerCountDown = cmp.dwTimerCountDown + 1

     'update the prompt message with the countdown value
      SetDlgItemText hwndMsgBox, IDPROMPT, _
                     "To start searching C: immediately, select Begin." & vbCrLf & _
                     "To select a different drive, press Select." & vbCrLf & vbCrLf & _
                     "Automatic searching of C: will begin in " & _
                     CStr(10 - cmp.dwTimerCountDown) & " seconds."
                            

     'if the timer has 'expired' (the
     'count=duration), we need to
     'programmatically 'press' the button
     'specified as the default on timeout
      If cmp.dwTimerCountDown = cmp.dwTimerDuration Then
      
        'we can kill this timer
         Timer1.Enabled = False
         
        'obtain the handle to the
        'button designated as default
        'if the timer expires
         hWndTargetBtn = GetDlgItem(hwndMsgBox, cmp.dwTimerExpireButton)
         
         If hWndTargetBtn <> 0 Then
         
           'set the focus to the target button and
           'simulate a click to close the dialog and
           'return the correct value
            Call PutFocus(hWndTargetBtn)
           
           'need a DoEvents to allow PutFocus
           'to actually put focus
            DoEvents
            
           'simulate a mouse click on the button
            Call PostMessage(hWndTargetBtn, WM_LBUTTONDOWN, 0, ByVal 0&)
            Call PostMessage(hWndTargetBtn, WM_LBUTTONUP, 0, ByVal 0&)
         
         End If
         
      End If
                                       
   End If
   
End Sub