SetWindowsHookEx not calling my callback? - c++

Question

Well I tried different solution to my problem but It just doesn't work.
I call SetWindowsHookExA and then when I press a key the messagebox is not shown. What to do?
this is my code (this is a DLL which is loaded by another DLL which is loaded by the program):
#include <Windows.h>
HINSTANCE gl_hThisInstance = NULL;
HHOOK hHook = NULL;
LRESULT CALLBACK KeyHit(int code,WPARAM wParam,LPARAM lParam);
BOOL APIENTRY DllMain( HANDLE hModule, DWORD ul_reason_for_call, LPVOID lpReserved)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
gl_hThisInstance = (HINSTANCE)hModule;
hHook = SetWindowsHookExA(
WH_KEYBOARD,
KeyHit,
//(HWND)gl_hThisInstance//not working
0,//not working
//(DWORD)gl_hThisInstance//not working
//GetCurrentThreadId()//even not working with this
0//not working
);
break;
}
return TRUE;
}
LRESULT CALLBACK KeyHit(int code,WPARAM wParam,LPARAM lParam)
{
MessageBox(0,"PRESSED","PRESSED",0);
return CallNextHookEx(hHook,code,wParam,lParam);
}

Answer 1

I got issues with the hooking before. Not really an issue, but the way I did it was not supposed to.
First of all, you should have 2 exported functions from the DLL, SetHook and RemoveHook. The SetHook function will call the SetWindowsHookEx() from there. If you ever try to call the SetWindowsHookEx() from within a thread or DLLMain of your DLL, the function returns no errors, but the callback function will never be called. It took me sometimes to figure it out.
Posted here is my working code to catch WH_GETMESSAGE, you can reference from here.
Here is my working exported SetHook() function from the DLL.
bool __declspec(dllexport) __stdcall SetHook(DWORD myWnd)
{
mySavedHook = SetWindowsHookEx(WH_GETMESSAGE,
GetMsgProc,
infoContainer.DllHModule,
myWnd);
int errorID = GetLastError();
if (errorID != 0)
{
MessageBoxA(NULL, "Failed to implement hook", "Failed", 0);
MessageBoxA(NULL, to_string(errorID).c_str(), "Error ID", 0);
return false;
}
else
{
return true;
}
}
infoContainer.DllHModule: instance of the DLL, which is the first parameter of DllMain().
myWnd: is my Thread ID (not Process ID) - Get it from GetWindowThreadProcessId(window_handle, NULL). To implement global hook, use 0 as myWnd.
And here is my callback function.
LRESULT CALLBACK GetMsgProc(int nCode, WPARAM wParam, LPARAM lParam)
{
if (nCode >= 0)
{
LPMSG msg = (LPMSG)lParam;
if (msg->message == WM_CALLFUNCTION)
{
MessageBoxA(NULL, "Receive WM_CALLFUNTION", "Good news", 0);
}
}
//Doesn't matter, just call this function and return it.
return CallNextHookEx(_hook, nCode, wParam, lParam);
}
The callback function must have the CALLBACK keyword to work.
From the external application, call the SetHook() from the DLL and use the Thread ID as its param.