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strange hook problem

rabbitears
rabbitears asked
on
Medium Priority
430 Views
Last Modified: 2010-04-10
how come my keyboard hook is only being caught from my program even though it is a system wide hook? here's how i'm calling SetWindowsHookEx:

hHook = SetWindowsHookEx(WH_KEYBOARD, (HOOKPROC)ShiftMonProc, (HINSTANCE)instance, NULL);

the rest of the relevant code looks like this:

BOOL AreModifiersOn(WORD wMod)
{
if(wMod & HOTKEYF_SHIFT)
if(!(GetKeyState(VK_SHIFT) & 0x80))
return FALSE;
if(wMod & HOTKEYF_CONTROL)
if(!(GetKeyState(VK_CONTROL) & 0x80))
return FALSE;
if(wMod & HOTKEYF_ALT)
if(!(GetKeyState(VK_MENU) & 0x80))
return FALSE;
return TRUE;
}


LRESULT CALLBACK ShiftMonProc(int nCode, WPARAM wParam, LPARAM lParam)
{
if (nCode == HC_ACTION)
if ((GetKeyState(hotkey) & 0x80) && AreModifiersOn(modkeys))
{
MessageBox(NULL, "oh", "yeah", MB_OK);
return TRUE;

}
return CallNextHookEx(hHook, nCode, wParam, lParam);
}

i could have sworn i had this code working earlier today but for some reason, it doesn't.. i'm running win '98, vc5, and MFC but the dll is just win32 api if it matters..
Comment
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Commented:
A systemwide hook MUST reside in a DLL.

Commented:
Here's an example:


////////////////////////////////////////////////////////////////////////////////
// Shared variables (must be initialized)

#pragma comment(linker, "-section:.shared,rws")
#pragma data_seg(".shared")

HHOOK g_hHook = NULL;     // WH_GETMESSAGE hook handle

#pragma data_seg()

////////////////////////////////////////////////////////////////////////////////
// Global variables

HINSTANCE g_hinstDll = NULL; // Current DLL instance handle

////////////////////////////////////////////////////////////////////////////////

// DLL initialization and termination routine

BOOL APIENTRY DllMain(HINSTANCE hinstDll, DWORD reason, LPVOID reserved)
{
    UNREFERENCED_PARAMETER(reserved);
   
    if (reason == DLL_PROCESS_ATTACH)
    {
        DisableThreadLibraryCalls(hinstDll);
        g_hinstDll = hinstDll;  // Save DLL instance handle
        break;
    }
   
    return TRUE; // Success
}

////////////////////////////////////////////////////////////////////////////////

// Set the hook

__declspec(dllexport) BOOL Hook(DWORD dwThreadId)
{
    // Is a hook allready in place
    if (g_hHook != NULL)
        return FALSE;
   
    g_hHook = SetWindowsHookEx(WH_CBT, CBTProc, g_hinstDll, dwThreadId);
    return (g_hHook != NULL);
   
}

////////////////////////////////////////////////////////////////////////////////
// Remove the hook

__declspec(dllexport) BOOL Unhook(void)
{
    BOOL rc;
   
    rc = UnhookWindowsHookEx(g_hHook);
    if (rc)
        g_hHook = NULL;
   
    return rc;
}

////////////////////////////////////////////////////////////////////////////////
// The hook procedure

__declspec(dllexport) LRESULT CALLBACK CBTProc(int code, WPARAM wParam, LPARAM
                                               lParam)
{
    /* Do whatever needed here... */
   
    // Pass through the hook chain
    return CallNextHookEx(g_hHook, code, wParam, lParam);
}

////////////////////////////////////////////////////////////////////////////////

I highly recommend Richter's "advanced windows" book.

Commented:
In case that wasn't clear: The example above is the DLL.

Author

Commented:
my hook IS in a dll and in fact, it looks almost exactly like the example you posted..

the full source for the dll is as follows.. (minus the comments and such)

#define STRICT
#include <windows.h>
#include <commctrl.h>

#define SHIFTMON_DLL
#include "shiftmon.h"

HHOOK hHook = NULL;
HINSTANCE instance;
WORD hotkey;
WORD modkeys;
int proportion;
int moveapp;

void SetDll(HWND parent)
{
      if (hHook == NULL)
      {
            hHook = SetWindowsHookEx(WH_KEYBOARD, (HOOKPROC)ShiftMonProc, (HINSTANCE)instance, NULL);
      }
      else
      {
            if (hHook)
            {
                  UnhookWindowsHookEx(hHook);
                  hHook = NULL;
            }

      }
}



void SetParams(WORD wHotKey, WORD wModKeys, int nProportion, int nMoveApp)
{
      hotkey = wHotKey;
      modkeys = wModKeys;
      proportion = nProportion;
      moveapp = nMoveApp;
}

BOOL AreModifiersOn(WORD wMod)
{
      if(wMod & HOTKEYF_SHIFT)
            if(!(GetKeyState(VK_SHIFT) & 0x80))
                  return FALSE;
      if(wMod & HOTKEYF_CONTROL)
            if(!(GetKeyState(VK_CONTROL) & 0x80))
                  return FALSE;
      if(wMod & HOTKEYF_ALT)
            if(!(GetKeyState(VK_MENU) & 0x80))
                  return FALSE;
      return TRUE;
}


LRESULT CALLBACK ShiftMonProc(int nCode, WPARAM wParam, LPARAM lParam)
{
      if (nCode == HC_ACTION)
            if ((GetKeyState(hotkey) & 0x80) && AreModifiersOn(modkeys))
            {
                  MessageBox(NULL, "oh", "yeah", MB_OK);
                  return TRUE;

            }
      return CallNextHookEx(hHook, nCode, wParam, lParam);
}

BOOL WINAPI DllMain(HANDLE hModule, ULONG dwReason, LPVOID lpReserved)
{
      if (dwReason == DLL_PROCESS_ATTACH)
            instance = (HINSTANCE)hModule;
      return TRUE;
}






Author

Commented:
errr, i just found out that the problem lies in the hook proc, if i comment out some of the code and just replace it with a messagebox, it works fine.. here's an example:

LRESULT CALLBACK ShiftMonProc(int nCode, WPARAM wParam, LPARAM lParam)
{
      if (nCode == HC_ACTION)
      {
            /*if ((GetKeyState(hotkey) & 0x80) && AreModifiersOn(modkeys))
            {
                  MessageBox(NULL, "oh", "yeah", MB_OK);
                  return TRUE;

            }
            */
            MessageBox(NULL, "oh", "yeah", MB_OK);
      }

      return CallNextHookEx(hHook, nCode, wParam, lParam);
}



of course this isn't a good idea :) and it doesn't get the job done, so what's wrong with the commented code?
Commented:
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Commented:
What value has the variable hotkey?

Commented:
And the autograder hits again!  I sometimes wonder why I bother at all...
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