Microsoft KB Archive/180936

= How To Position a MsgBox Using a Windows Hook Procedure =

Article ID: 180936

Article Last Modified on 3/11/2005

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APPLIES TO


 * Microsoft Visual Basic 5.0 Learning Edition
 * Microsoft Visual Basic 6.0 Learning Edition
 * Microsoft Visual Basic 5.0 Professional Edition
 * Microsoft Visual Basic 6.0 Professional Edition
 * Microsoft Visual Basic 5.0 Enterprise Edition
 * Microsoft Visual Basic 6.0 Enterprise Edition

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This article was previously published under Q180936



SUMMARY
This article illustrates how to position a message box on the screen.



MORE INFORMATION
You can create a CBT hook for your application so that it receives notifications when windows are created and destroyed. If you display a message box with this CBT hook in place, your application will receive a HCBT_ACTIVATE message when the message box is activated. Once you receive this HCBT_ACTIVATE message, you can position the window with the SetWindowPos API function and then release the CBT hook if it is no longer needed.

Step-by-Step Example
 Start a new Standard EXE project. Form1 is created by default.  Add a module to the project and add the following code to the new module: Type RECT Left As Long Top As Long Right As Long Bottom As Long End Type

Public Declare Function UnhookWindowsHookEx Lib "user32" ( _        ByVal hHook As Long) As Long Public Declare Function GetWindowLong Lib "user32" Alias _ "GetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long) _ As Long Public Declare Function GetCurrentThreadId Lib "kernel32" As Long Public 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 Public Declare Function SetWindowPos Lib "user32" ( _        ByVal hwnd As Long, ByVal hWndInsertAfter As Long, _         ByVal x As Long, ByVal y As Long, ByVal cx As Long, _         ByVal cy As Long, ByVal wFlags As Long) As Long Public Declare Function GetWindowRect Lib "user32" (ByVal hwnd _        As Long, lpRect As RECT) As Long

Public Const GWL_HINSTANCE = (-6) Public Const SWP_NOSIZE = &H1 Public Const SWP_NOZORDER = &H4 Public Const SWP_NOACTIVATE = &H10 Public Const HCBT_ACTIVATE = 5 Public Const WH_CBT = 5

Public hHook As Long

Function WinProc1(ByVal lMsg As Long, ByVal wParam As Long, _        ByVal lParam As Long) As Long

If lMsg = HCBT_ACTIVATE Then 'Show the MsgBox at a fixed location (0,0) SetWindowPos wParam, 0, 0, 0, 0, 0, _ SWP_NOSIZE Or SWP_NOZORDER Or SWP_NOACTIVATE 'Release the CBT hook UnhookWindowsHookEx hHook End If        WinProc1 = False

End Function

Function WinProc2(ByVal lMsg As Long, ByVal wParam As Long, _        ByVal lParam As Long) As Long

Dim rectForm As RECT, rectMsg As RECT Dim x As Long, y As Long

'On HCBT_ACTIVATE, show the MsgBox centered over Form1 If lMsg = HCBT_ACTIVATE Then 'Get the coordinates of the form and the message box so that 'you can determine where the center of the form is located GetWindowRect Form1.hwnd, rectForm GetWindowRect wParam, rectMsg x = (rectForm.Left + (rectForm.Right - rectForm.Left) / 2) - _ ((rectMsg.Right - rectMsg.Left) / 2) y = (rectForm.Top + (rectForm.Bottom - rectForm.Top) / 2) - _ ((rectMsg.Bottom - rectMsg.Top) / 2) 'Position the msgbox SetWindowPos wParam, 0, x, y, 0, 0, _ SWP_NOSIZE Or SWP_NOZORDER Or SWP_NOACTIVATE 'Release the CBT hook UnhookWindowsHookEx hHook End If        WinProc2 = False

End Function

 Add two CommandButtons to Form1.  Add the following code to Form1: Private Sub Command1_Click Dim hInst As Long Dim Thread As Long

'Set up the CBT hook hInst = GetWindowLong(Me.hwnd, GWL_HINSTANCE) Thread = GetCurrentThreadId hHook = SetWindowsHookEx(WH_CBT, AddressOf WinProc1, hInst, _                                 Thread)

'Display the message box MsgBox "This message box has been positioned at (0,0)."

End Sub

Private Sub Command2_Click Dim hInst As Long Dim Thread As Long

'Set up the CBT hook hInst = GetWindowLong(Me.hwnd, GWL_HINSTANCE) Thread = GetCurrentThreadId hHook = SetWindowsHookEx(WH_CBT, AddressOf WinProc2, hInst, _                                 Thread)

'Display the message box MsgBox "This message box is centered over Form1." End Sub

 Press the F5 key to run the program. Click Command1 and the message box appears at the upper-left corner of the screen (0,0). Click OK to dismiss the message box. Click Command2 and the message box appears at the center of Form1. Click OK to dismiss the message box.

