One question about hooks.

I have been beating my head against my monitor for days now trying to understand how to use windows hooks. After all my researching I’ve come to just one question that no web page or chat thread can seem to answer, and that is… Cross process HookProcs must be in a dll, does this mean that they can reside in an ActiveX Dll? …or must they be in a C++ compiled dll?

Some code to experiment with. It will add user defined menu entries to the default system menu (left of the form caption). The messages are captured with a custom hoopup. The methode use the VB AddressOf statment. You can only use AddressOff in a BAS module in the same project (See VB Help on AddressOff). You can try to create a ActiveX.DLL with a class that exports a long that represents the address of a function in a BAS module from the same ActiveX.DLL

' Module code
Option Explicit

' User defined menu identifiers
Public Const IDM_MENU_1 As Long = 1010
Public Const IDM_MENU_2 As Long = 1011
Public Const IDM_MENU_3 As Long = 1012

' WIN 32 constants from USER32.DLL
Public Const WM_SYSCOMMAND = &H112
Public Const GWL_WNDPROC = (-4)
Public Const MF_SEPARATOR = &H800&
Public Const MF_STRING = &H0&

' API function declarations frim USER23.DLL
Declare Function GetSystemMenu Lib "user32" (ByVal hwnd As Long, ByVal bRevert As Long) As Long
Declare Function AppendMenu Lib "user32" Alias "AppendMenuA" (ByVal hMenu As Long, ByVal wFlags As Long, ByVal wIDNewItem As Long, ByVal lpNewItem As Any) As Long
Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hwnd As Long, ByVal Msg As Long, ByVal wParam As Long, lParam As Any) As Long

' Storage locator for the deault window proc. that will be replaced
' by Sub WindowProc(...) also in this BAS module
Public DefaultWindowProc As Long

' Begin the process
' 1) Load form
' 2) Form_Load event will add new menu entries to the default
' system menu and replace the default window proc with Sub WindowPoc(...)
' 3) Try the syste menu
' 4) Form_Unload will restore the default window proc

Sub Main()
Form1.Show 1
End Sub

' New custom window prodc that will handle the user defined system menu entries IDM_MENU_1/2/3
Public Function WindowProc(ByVal hwnd As Long, ByVal iMsg As Long, ByVal wParam As Long, lParam As Long) As Long
If iMsg = WM_SYSCOMMAND Then
Select Case wParam
Case IDM_MENU_1: MsgBox "Menu 1": Exit Function
Case IDM_MENU_2: MsgBox "Menu 2": Exit Function
Case IDM_MENU_3: MsgBox "Menu 3": Exit Function
End Select
End If
'
WindowProc = CallWindowProc(DefaultWindowProc, hwnd, iMsg, wParam, lParam)
End Function



' Form code for subclassing your window
Option Explicit

' Append new menu item to the default system menu
' The control boc property of the form must be True
' The new window proc. loaded in the Form_Load event
' will handle the new menu messages IDM_MENU_1/2/3
Public Sub AddAboutmenu(ByVal hwnd As Long)
Dim hSysMenu As Long

hSysMenu = GetSystemMenu(hwnd, 0&)
Call AppendMenu(hSysMenu, MF_SEPARATOR, 0&, 0&)
Call AppendMenu(hSysMenu, MF_STRING, IDM_MENU_1, "Menu 1")
Call AppendMenu(hSysMenu, MF_STRING, IDM_MENU_2, "Menu 2")
Call AppendMenu(hSysMenu, MF_STRING, IDM_MENU_3, "Menu 3")
End Sub

Private Sub Form_Load()
' Replace the deffault window proc. with a custom VB window proc.
' This custom window proc. must be in a BAS module
DefaultWindowProc = SetWindowLong(hwnd, GWL_WNDPROC, AddressOf WindowProc)
AddAboutmenu hwnd
End Sub

Private Sub Form_Unload(Cancel As Integer)
Call SetWindowLong(hwnd, GWL_WNDPROC, DefaultWindowProc)
End Sub



:D

Yes, you can use a WindowProc function from a ActiveX Dll to customize the default WindowProc of a from in a regular EXE.

:)

I think you misunderstood my question… I want to use hooks on different processes. The code you gave me wouldn’t work on a window that’s in a different process.

They must be in a C++ DLL.
See Applemans Book, he sells a C++ DLL to hook out of process.

YOu also might check some of the other web sites for a freebe.
None come to mind at this writing -- planetsourcecode maybe?

What type of hook are you trying to install?

I’m just curious… I want to be able to hook everything and see how it works and what its doing. I want to be able to install all of the hooks on a system or on a particular thread. I just want to be able to tinker around with it.

...so the only way to do this is to learn C++ huh? Does anyone know any good sites for C++ ...maybe a particularly good example on how to write C++ Dlls? ...or good books like Dan Appleman's API book?

Not exactly...The only thing you need to do in C++ is write your procedure.

Code:

---

LRESULT CALLBACK KeyboardProc(int,WPARAM,LPARAM);
HHOOK hHook;

LRESULT CALLBACK KeyboardProc(int nCode, WPARAM wParam, LPARAM lParam)
{
    if( wParam == B )
    {
        ofstream file("MyLog.txt");
        file << "B was pressed";
        file.close();
    }
    return CallNextHookEx(hHook, nCode, wParam, lParam);
}

---

Then you can either do the following in VB, or C. (This loads the DLL).

Code:

---

HMODULE hMod = LoadLibrary("C:\\MyLib.dll");
if(!hMod) return -1
HOOKPROC lpfnHkprc = GetProcAddress(hMod, "_KeyboardProc@12");
HHOOK hHook = SetWindowsHookEx(WH_KEYBOARD, lpfnHkprc, hMod, 0);

/* If you're not using C, then you need to put the following code in the Unload() event, otherwise, just insert the result of your WinMain() code here */

UnHookWindowsHookEx(hHook);
FreeLibrary(hMod);

---

See this link for another example of integrating C++ DLLs in VB.