SetWindowsHookEx failing : setwindowshookex

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09.14.2007 at 04:47AM PDT, ID: 22828574

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7.8

SetWindowsHookEx failing

Zone: Windows Programming

Tags: setwindowshookex

Following on from my question at: http://www.experts-exchange.com/Programming/System/Windows__Programming/Q_22828041.html

The call to SetWindowsHookEx function seems to be failing. I've checked the dllMain method doesn't seem to get called at any time either:

      BOOL WINAPI dllMain(HINSTANCE aHInstance, DWORD aReason, LPVOID aVoid){
            MessageBox(0, "Start", "", 0);
            if(aReason==DLL_PROCESS_ATTACH){
                  hInstance=aHInstance;
                  MessageBox(0, "On", "", 0);
            }
            if(aReason==DLL_PROCESS_DETACH){
                  removeKeyHook();
                  MessageBox(0, "Off", "", 0);
            }
            return true;
      }

Thanks,
Uni

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Question Stats

Zone: Programming

Question Asked By: Unimatrix_001

Solution Provided By: jkr

Participating Experts: 2

Solution Grade: A

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09.14.2007 at 09:06AM PDT, ID: 19892775

Rank: Guru

AlexFM:

Looking at your code, I guess it fails because you pass incorrect HINSTANCE parameter to the SetWindowsEx function. This should be result of LoadLibrary function and not HINSTANCE passed to DllMain.
Try to get the same library handle using LoadLibrary. If this doesn't help, place hook callback function to separate Dll. Dll which is called by VB client belongs to this client process. For global hook, Windows needs to inject Dll to another processes, this is why LoadLibrary is used.

For most Windows API you can get additional error information by using GetLastError, this helps to find the reason of the fault.

09.14.2007 at 09:10AM PDT, ID: 19892808

Unimatrix_001:

Does that mean from the VB application I need to specifically call the dllMain method? If so, what do I put as the DWORD aReason and LPVOID aVoid parameters?

09.14.2007 at 09:24AM PDT, ID: 19892921

Rank: Guru

AlexFM:

No, your VB code is OK. Dll hook code must be changed. WinMain is called by Windows when it loads Dll to a process address space.
Just change Dll code. First try to replace HINSTANCE parameter with result of LoadLibrary. In Dll you know Dll name, this should not be problem. If this doesn't help, move hook callback function to another Dll, load it using LoadLibrary and use handle returned by LoadLibrary in SetWindowsHookEx call.

09.14.2007 at 09:27AM PDT, ID: 19892939

Unimatrix_001:

>>Just change Dll code. First try to replace HINSTANCE parameter with result of LoadLibrary.
I don't call LoadLibrary inside the DLL?

>>If this doesn't help, move hook callback function to another Dll, load it using LoadLibrary and use handle returned by LoadLibrary in SetWindowsHookEx call.
This would mean I'd have a VB application and two DLL's???

09.14.2007 at 09:36AM PDT, ID: 19893027

Rank: Guru

AlexFM:

I don't see any LoadLibrary call in your code.
Try this:

__declspec(dllexport) bool setKeyHook(){
if(messageHook==NULL){
HMODULE h = LoadLibrary("Hook.dll");
HOOKPROC hProc = (HOOKPROC)GetProcAddress(h, "messageProc");
messageHook=SetWindowsHookEx(WH_GETMESSAGE, hProc, h, 0);
if(messageHook==NULL){
return false;
}
}
return true;
}

If this still doesn't work, try to use second library.
Agan, please check return code and call GetLastError after every function.

09.14.2007 at 10:05AM PDT, ID: 19893267

Unimatrix_001:

This is getting quite confusing now...

>>I don't see any LoadLibrary call in your code.
That's because there isn't one...

My VB calls LoadLibrary on hook.dll to load the dll, why do I need to call:
HMODULE h = LoadLibrary("Hook.dll");
from within the Hook.dll (which would load itself?) when it has already been loaded by the VB application.

09.14.2007 at 10:18AM PDT, ID: 19893377

Rank: Genius

jkr:

Just store the HINSTANCE that is passed in the hook DLL's 'HINSTANCE' parameter and use that for 'SetWindowsHookEx()'.

09.14.2007 at 10:19AM PDT, ID: 19893383

Rank: Genius

jkr:

... or use

HINSTANCE hInst = GetModuleHandle("hook.dll");

which will return the same information.

09.14.2007 at 10:26AM PDT, ID: 19893459

Unimatrix_001:

Hi jkr,

Thanks, that works wonderful. :) Do I need the dllMain method then, as the "start" message doesn't even fire (see code at the top of this page)?

Uni.

09.14.2007 at 10:47AM PDT, ID: 19893638

Rank: Genius

jkr:

Actually, you should make that a 'DllMain()', the 1st 'D' has to be capital..

09.14.2007 at 10:49AM PDT, ID: 19893661

Unimatrix_001:

>>Actually, you should make that a 'DllMain()', the 1st 'D' has to be capital..
:S I thought the method name was irrelevant and it matched the method by the paramters and return type???

Although even so, do I require it?

Thanks,
Uni

09.14.2007 at 10:50AM PDT, ID: 19893674

Unimatrix_001:

Also, do I need to add 'extern "C" __declspec(dllexport)' to it and do I need to specifically call it from the VB app?

09.14.2007 at 12:44PM PDT, ID: 19894600

Rank: Genius

jkr:

No, the case must match. Let me put it like that: A DLL entry point has some advantaged, so it won't hurt to have one. However there are some limitations about what you are allowed to do there. I have the habit to add one, even if only for debugging purposes. And no, no need to export it nor to call it directly, the system loader will do that for you.

Accepted Solution

09.14.2007 at 07:27PM PDT, ID: 19896238

Unimatrix_001:

Thank you. :)

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