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strange hook problem

Posted on 1998-07-12
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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..
0
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Question by:rabbitears
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8 Comments
 
LVL 11

Expert Comment

by:alexo
ID: 1167590
A systemwide hook MUST reside in a DLL.
0
 
LVL 11

Expert Comment

by:alexo
ID: 1167591
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.
0
 
LVL 11

Expert Comment

by:alexo
ID: 1167592
In case that wasn't clear: The example above is the DLL.
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Author Comment

by:rabbitears
ID: 1167593
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;
}






0
 

Author Comment

by:rabbitears
ID: 1167594
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?
0
 
LVL 11

Accepted Solution

by:
alexo earned 100 total points
ID: 1167595
I'm surprised your code works at all.  You see, your hHook variable must reside in shared memory, otherwise each instance of the DLL will get its own copy of it and the setting/resetting of the hook will get screwed up.

The other global variables that you use are also local to each process so you should put them into the shared section as well.  Otherwise, SetParams() will only operate on the copy of the variables local to it's process.

If you're programming under MSVC do:

    #pragma comment(linker, "-section:.shared,rws")
    #pragma data_seg(".shared")
    HHOOK hHook = NULL;
    // Other shared variables here...
    #pragma data_seg()

For Borland, the procedure is a bit more complicated.

BTW, when you post code on EE, use spaces instead of tabs to preserve the formatting.
0
 
LVL 1

Expert Comment

by:timop
ID: 1167596
What value has the variable hotkey?
0
 
LVL 11

Expert Comment

by:alexo
ID: 1167597
And the autograder hits again!  I sometimes wonder why I bother at all...
0

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