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Position a MsgBox Using a Windows Hook Procedure
Step-by-Step Example
[ol]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
WinProc = 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
WinProc = False End FunctionAdd 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 SubPress 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. [/ol] |
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