DOCUMENT:Q180936 11-JAN-2001 [vbwin] TITLE :HOWTO: Position a MsgBox Using a Windows Hook Procedure PRODUCT :Microsoft Visual Basic for Windows PROD/VER:WINDOWS:5.0,6.0 OPER/SYS: KEYWORDS:kbGrpDSVB ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 - Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 - Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 ------------------------------------------------------------------------------- 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 -------------------- 1. Start a new Standard EXE project. Form1 is created by default. 2. 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 3. Add two CommandButtons to Form1. 4. 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 5. 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. REFERENCES ========== For additional information about creating message hooks with Visual Basic, please see the following articles in the Microsoft Knowledge Base: Q168795 : HOWTO: Hook Into a Window's Messages Using AddressOf Q170570 : HOWTO: Build a Windows Message Handler with AddressOf in VB5 Additional query words: MessageBox kbVBp500 kbVBp600 kbVBp kbdsd kbDSupport KBWIN32SDK KBAPI ====================================================================== Keywords : kbGrpDSVB Technology : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600 Version : WINDOWS:5.0,6.0 Issue type : kbhowto ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.