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Oleg Gashev (2001-11-13 22:20) [2]

Monitoring System Events

The following example uses a variety of thread-specific hook procedures to monitor the system for events affecting a thread. It demonstrates how to process events for the following types of hook procedures:

WH_CALLWNDPROC
WH_CBT
WH_DEBUG
WH_GETMESSAGE
WH_KEYBOARD
WH_MOUSE
WH_MSGFILTER
The user can install and remove a hook procedure by using the menu. When a hook procedure is installed and an event that is monitored by the procedure occurs, the procedure writes information about the event to the client area of the application"s main window.

#define NUMHOOKS 7

// Global variables

typedef struct _MYHOOKDATA
{
int nType;
HOOKPROC hkprc;
HHOOK hhook;
} MYHOOKDATA;

MYHOOKDATA myhookdata[NUMHOOKS];

LRESULT WINAPI MainWndProc(HWND hwndMain, UINT uMsg, WPARAM wParam,
LPARAM lParam)
{
static BOOL afHooks[NUMHOOKS];
int index;
static HMENU hmenu;

switch (uMsg)
{
case WM_CREATE:

// Save the menu handle.

hmenu = GetMenu(hwndMain);

// Initialize structures with hook data. The menu-item
// identifiers are defined as 0 through 6 in the
// header file. They can be used to identify array
// elements both here and during the WM_COMMAND
// message.

myhookdata[IDM_CALLWNDPROC].nType = WH_CALLWNDPROC;
myhookdata[IDM_CALLWNDPROC].hkprc = CallWndProc;
myhookdata[IDM_CBT].nType = WH_CBT;
myhookdata[IDM_CBT].hkprc = CBTProc;

myhookdata[IDM_DEBUG].nType = WH_DEBUG;
myhookdata[IDM_DEBUG].hkprc = DebugProc;
myhookdata[IDM_GETMESSAGE].nType = WH_GETMESSAGE;
myhookdata[IDM_GETMESSAGE].hkprc = GetMsgProc;
myhookdata[IDM_KEYBOARD].nType = WH_KEYBOARD;
myhookdata[IDM_KEYBOARD].hkprc = KeyboardProc;
myhookdata[IDM_MOUSE].nType = WH_MOUSE;
myhookdata[IDM_MOUSE].hkprc = MouseProc;
myhookdata[IDM_MSGFILTER].nType = WH_MSGFILTER;

myhookdata[IDM_MSGFILTER].hkprc = MessageProc;

// Initialize all flags in the array to FALSE.

memset(afHooks, FALSE, sizeof(afHooks));

return 0;

case WM_COMMAND:
switch (LOWORD(wParam))
{
// The user selected a hook command from the menu.

case IDM_CALLWNDPROC:
case IDM_CBT:
case IDM_DEBUG:
case IDM_GETMESSAGE:

case IDM_KEYBOARD:
case IDM_MOUSE:
case IDM_MSGFILTER:

// Use the menu-item identifier as an index
// into the array of structures with hook data.

index = LOWORD(wParam);

// If the selected type of hook procedure isn"t
// installed yet, install it and check the
// associated menu item.

if (!afHooks[index])
{
myhookdata[index].hhook = SetWindowsHookEx(
myhookdata[index].nType,
myhookdata[index].hkprc,
(HINSTANCE) NULL, GetCurrentThreadId());
CheckMenuItem(hmenu, index,
MF_BYCOMMAND | MF_CHECKED);
afHooks[index] = TRUE;

}

// If the selected type of hook procedure is
// already installed, remove it and remove the
// check mark from the associated menu item.

else
{
UnhookWindowsHookEx(myhookdata[index].hhook);
CheckMenuItem(hmenu, index,
MF_BYCOMMAND | MF_UNCHECKED);
afHooks[index] = FALSE;

}

default:
return (DefWindowProc(hwndMain, uMsg, wParam,
lParam));
}
break;

//
// Process other messages.
//

default:
return DefWindowProc(hwndMain, uMsg, wParam, lParam);
}
return NULL;
}

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