BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  DLL <-> Form communication problem (Gloobal Key hook)          BorlandTalk.com Forum Index -> C++ Builder (Language C++) View previous topic :: View next topic   Author Message Stan R. Guest Posted: Fri Nov 25, 2005 2:28 am    Post subject: DLL <-> Form communication problem (Gloobal Key hook) I'm trying to write an application that creates a global key hook. I have the MainForm project and the DLL project in a project group. I can't seem to get this working right. If I uncomment the ShowMessage in the KeyboardProc function, it comes up on keystroke TWICE. Why is this? Also, when that line is uncommented, I see the character added to my memo (I'm only using that for testing as I'm trying to learn how to do this right.) But if I comment it, I dont see anything added to the the memo. Or am I going abou this the wrong way? KeyCap_MainForm.h: [...] publuc: [...] bool __fastcall OnSystemKeyStroke(char Key); KeyCap_MainForm.cpp: [...] typedef bool (__stdcall *DLLFunc_SetHook) (TKeyCapForm *KeyCapForm); typedef bool (__stdcall *DLLFunc_UnsetHook)(void); DLLFunc_SetHook SetHook; DLLFunc_UnsetHook UnsetHook; HINSTANCE DllHandle; //------------------------------------------------------------------------------ __fastcall TKeyCapForm::TKeyCapForm(TComponent* Owner) // constructor : TForm(Owner) { // LOAD DLL DllHandle = LoadLibrary("KeyCap.dll"); if (DllHandle != NULL) { SetHook = (DLLFunc_SetHook)GetProcAddress(DllHandle, "SetHook"); // To set the keyboard hook if (SetHook != NULL) { if (!SetHook(this)) ShowMessage("Can't set hook"); } } } //------------------------------------------------------------------------------ __fastcall TKeyCapForm::~TKeyCapForm() { // Destructor if (DllHandle != NULL) { UnsetHook = (DLLFunc_UnsetHook)GetProcAddress(DllHandle, "UnsetHook"); // To release the keyboard hook if (UnsetHook != NULL) { if (!UnsetHook()) ShowMessage("Can't unset hook"); } } } //------------------------------------------------------------------------------ bool __fastcall TKeyCapForm::OnSystemKeyStroke(char Key) { /*if (wParam == VK_SNAPSHOT) { // Print Screen key caught, do something // return 0 to allow Windows to finish processing the key // or return non-zero to prevent further processing return 1; } else return 0;*/ // Add a line to the Memo. Out->Lines->Add(Key); return 1; } //------------------------------------------------------------------------------ KeyCap_DLL.cpp: #include <vcl.h> #include <windows.h> #include "KeyCap_MainForm.h" #pragma hdrstop #pragma argsused HINSTANCE DllInstance; HHOOK KeyHookHandle; TKeyCapForm *Form; //------------------------------------------------------------------------------ extern "C" { BOOL __declspec(dllexport) __stdcall SetHook(TKeyCapForm *KeyCapForm); BOOL __declspec(dllexport) __stdcall UnsetHook(void); } //------------------------------------------------------------------------------ LRESULT CALLBACK KeyboardProc(int code, WPARAM wParam, LPARAM lParam){ if (code < 0) return CallNextHookEx(KeyHookHandle, code, wParam, lParam); //ShowMessage("Test [" + String((char)wParam) + "]"); // Use TKeyCapForm::OnSystemKeyStroke function to handle this ! return Form->OnSystemKeyStroke((char)wParam); } //------------------------------------------------------------------------------ BOOL __stdcall SetHook(TKeyCapForm *KeyCapForm) { KeyHookHandle = SetWindowsHookEx(WH_KEYBOARD, (HOOKPROC)KeyboardProc, DllInstance, 0); Form = KeyCapForm; return (KeyHookHandle != NULL); } //------------------------------------------------------------------------------ BOOL __stdcall UnsetHook(void) { BOOL ret = TRUE; if (KeyHookHandle != NULL) { ret = UnhookWindowsHookEx(KeyHookHandle); if (ret == TRUE) KeyHookHandle = NULL; } return ret; } //------------------------------------------------------------------------------ int WINAPI DllEntryPoint(HINSTANCE hinst, unsigned long reason, void* lpReserved) { DllInstance = hinst; return 1; } //------------------------------------------------------------------------------ -- Stan R. Back to top Remy Lebeau (TeamB) Guest Posted: Fri Nov 25, 2005 8:05 am    Post subject: Re: DLL <-> Form communication problem (Gloobal Key hook) "Stan R." <none@none> wrote Quote: I can't seem to get this working right. That is because your code is not implementing the hook correctly. You must export the callback function, and you must share the DLL's hook-related data across multiple instances of your DLL. Try this code instead: --- KeyCap_MainForm.h --- #include "KeyCap_DLL.h" class TKeyCapForm : public TForm { //... private: MESSAGE void __fastcall OnSystemKeyStroke(TMessage &Message); //... protected: virtual void __fastcall CreateWindowHandle(const TCreateParams &Params); virtual void __fastcall DestroyWindowHandle(void); //... public: //... BEGIN_MESSAGE_MAP VCL_MESSAGE_HANDLER(WM_SYSKEYSTROKE, TMessage, OnSystemKeyStroke) END_MESSAGE_MAP(TForm) }; --- KeyCap_MainForm.cpp --- #include "KeyCap_MainForm.h" DLLFunc_InstallHook lpInstallHook = NULL; DLLFunc_UninstallHook lpUninstallHook = NULL; DLLFunc_SetHookWnd lpSetHookWnd = NULL; HINSTANCE DllHandle = NULL; __fastcall TKeyCapForm::TKeyCapForm(TComponent* Owner) : TForm(Owner) { DllHandle = LoadLibrary("KeyCap.dll"); if( DllHandle != NULL ) { lpInstallHook = (DLLFunc_InstallHook) GetProcAddress(DllHandle, "InstallHook"); lpUninstallHook = (DLLFunc_UninstallHook) GetProcAddress(DllHandle, "UninstallHook"); lpSetHookWnd = (DLLFunc_SetHookWnd) GetProcAddress(DllHandle, "SetHookWnd"); if( (lpInstallHook != NULL) && (lpUninstallHook != NULL) && (lpSetHookWnd != NULL) ) { if( lpInstallHook() ) return; ShowMessage("Can't install hook"); } else ShowMessage("Can't load hook functions"); FreeLibrary(DllHandle); DllHandle = NULL; } else ShowMessage("Can't load hook dll"); } __fastcall TKeyCapForm::~TKeyCapForm() { if( DllHandle != NULL ) { if( !lpUninstallHook() ) ShowMessage("Can't uninstall hook"); FreeLibrary(DllHandle); } } void __fastcall TKeyCapForm::CreateWindowHandle(const TCreateParams &Params) { TForm::CreateWindowHandle(Params); if( HandleAllocated() && (lpSetHookWnd != NULL) ) lpSetHookWnd(Handle); } void __fastcall TKeyCapForm::DestroyWindowHandle(void) { TForm::DestroyWindowHandle(); if( lpSetHookWnd != NULL ) lpSetHookWnd(NULL); } void __fastcall TKeyCapForm::OnSystemKeyStroke(TMEssage &Message) { // return 0 to allow Windows to finish processing the key // or return non-zero to prevent further processing /* if( Message.LParam == VK_SNAPSHOT ) { // Print Screen key caught, do something Message.Result = 1; } */ // Add a line to the Memo. Out->Lines->Add("Key: " + AnsiString(Message.WParam) + ", Flags: " + AnsiString(Message.LParam)); Message.Result = 0; } --- KeyCap_DLL.h --- #ifndef KeyCapDLLH #define KeyCapDLLH #define WM_SYSKEYSTROKE (WM_USER + 100) #ifdef BUILDING_DLL #define EXPORT __declspec(dllexport) #else #define EXPORT __declspec(dllimport) #endif #ifdef __cplusplus extern "C" { #endif EXPORT BOOL __stdcall InstallHook(void); EXPORT BOOL __stdcall UninstallHook(void); EXPORT void __stdcall SetHookWnd(HWND hwnd); EXPORT LRESULT CALLBACK KeyboardProc(int code, WPARAM wParam, LPARAM lParam); typedef BOOL (__stdcall *DLLFunc_InstallHook) (void); typedef BOOL (__stdcall *DLLFunc_InstallHook)(void); typedef void (__stdcall *DLLFunc_SetHookWnd)(HWND); #ifdef __cplusplus } #endif #endif --- KeyCap_DLL.cpp --- #include <windows.h> #pragma hdrstop #define BUILDING_DLL #include "KeyCap_DLL.h" typedef struct { HWND hWnd; HHOOK hHook; } THookInfo, *PHookInfo; HINSTANCE DllInstance = NULL; HANDLE hMapping = NULL; PHookInfo pHookInfo = NULL; int WINAPI DllEntryPoint(HINSTANCE hinst, unsigned long reason, void* lpReserved) { switch( reason ) { case DLL_PROCESS_ATTACH: { DllInstance = hinst; hMapping = CreateFileMapping( INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, 0, sizeof(THookInfo), TEXT("KeyCapHookInfo")); if( hMapping != NULL ) { bool bCreated = (GetLastError() != ERROR_ALREADY_EXISTS); pHookInfo = (PHookInfo) MapViewOfFile( hMapping, FILE_MAP_WRITE, 0, 0, 0); if( pHookInfo != NULL ) { if( bCreated == true ) { pHookInfo->hWnd = NULL; pHookInfo->hHook = NULL; } return 1; } CloseHandle(hMapping); hMapping = NULL; } break; } case DLL_PROCESS_DETACH: { if( pHookInfo ) UnmapViewOfFile(pHookInfo); if( hMapping ) CloseHandle(hMapping); break; } } return 0; } BOOL __stdcall InstallHook(void) { if( pHookInfo->hHook == NULL ) pHookInfo->hHook = SetWindowsHookEx(WH_KEYBOARD, (HOOKPROC)KeyboardProc, DllInstance, 0); return (pHookInfo->hHook != NULL); } BOOL __stdcall UninstallHook(void) { if( pHookInfo->hHook != NULL ) { if( UnhookWindowsHookEx(pHookInfo->hHook) ) pHookInfo->hHook = NULL; } return (pHookInfo->hHook == NULL); } void __stdcall SetHookWnd(HWND hwnd) { pHookInfo->hWnd = hwnd; } LRESULT CALLBACK KeyboardProc(int code, WPARAM wParam, LPARAM lParam) { if( (code == HC_ACTION) && (pHookInfo->hWnd != NULL) ) { int iRet = SendMessage(pHookInfo->hWnd, WM_SYSKEYSTROKE , wParam, lParam); if( iRet != 0 ) return iRet; } return CallNextHookEx(pHookInfo->hHook, code, wParam, lParam); } Gambit Back to top Stan R. Guest Posted: Fri Nov 25, 2005 11:26 pm    Post subject: Re: DLL <-> Form communication problem (Gloobal Key hook) Remy Lebeau (TeamB) wrote: Quote: "Stan R." <none@none> wrote in message news:438676bf (AT) newsgroups (DOT) borland.com... I can't seem to get this working right. That is because your code is not implementing the hook correctly. You must export the callback function, and you must share the DLL's hook-related data across multiple instances of your DLL. Try this code instead: [snip code] Thank you very much. I only ask one more thing, I would like to know why the code I posted was kinda partially working though? I just want to under stand this more. What I saw happening was, when it would worked, it would seem to trigger twice for each key stroke. It seemed to stop working when my main form window lost focus, though it did work at least once when I switched to another appand pressed a key and stopped workign after that. Again, I just want to have a greater understanding for this stuff. It's godo to be given the correct way, but it's also better to know why exactly the not so good way /was/ not so good :) Thank you. Back to top Stan R. Guest Posted: Sat Nov 26, 2005 12:46 am    Post subject: Re: DLL <-> Form communication problem (Gloobal Key hook) Remy Lebeau (TeamB) wrote: Quote: "Stan R." <none@none> wrote in message news:438676bf (AT) newsgroups (DOT) borland.com... I can't seem to get this working right. That is because your code is not implementing the hook correctly. You must export the callback function, and you must share the DLL's hook-related data across multiple instances of your DLL. Try this code instead: --- KeyCap_MainForm.h --- #include "KeyCap_DLL.h" class TKeyCapForm : public TForm { //... private: MESSAGE void __fastcall OnSystemKeyStroke(TMessage &Message); //... protected: virtual void __fastcall CreateWindowHandle(const TCreateParams &Params); virtual void __fastcall DestroyWindowHandle(void); //... public: //... BEGIN_MESSAGE_MAP VCL_MESSAGE_HANDLER(WM_SYSKEYSTROKE, TMessage, OnSystemKeyStroke) END_MESSAGE_MAP(TForm) }; --- KeyCap_MainForm.cpp --- #include "KeyCap_MainForm.h" DLLFunc_InstallHook lpInstallHook = NULL; DLLFunc_UninstallHook lpUninstallHook = NULL; DLLFunc_SetHookWnd lpSetHookWnd = NULL; HINSTANCE DllHandle = NULL; __fastcall TKeyCapForm::TKeyCapForm(TComponent* Owner) : TForm(Owner) { DllHandle = LoadLibrary("KeyCap.dll"); if( DllHandle != NULL ) { lpInstallHook = (DLLFunc_InstallHook) GetProcAddress(DllHandle, "InstallHook"); lpUninstallHook = (DLLFunc_UninstallHook) GetProcAddress(DllHandle, "UninstallHook"); lpSetHookWnd = (DLLFunc_SetHookWnd) GetProcAddress(DllHandle, "SetHookWnd"); if( (lpInstallHook != NULL) && (lpUninstallHook != NULL) && (lpSetHookWnd != NULL) ) { if( lpInstallHook() ) return; ShowMessage("Can't install hook"); } else ShowMessage("Can't load hook functions"); FreeLibrary(DllHandle); DllHandle = NULL; } else ShowMessage("Can't load hook dll"); } __fastcall TKeyCapForm::~TKeyCapForm() { if( DllHandle != NULL ) { if( !lpUninstallHook() ) ShowMessage("Can't uninstall hook"); FreeLibrary(DllHandle); } } void __fastcall TKeyCapForm::CreateWindowHandle(const TCreateParams &Params) { TForm::CreateWindowHandle(Params); if( HandleAllocated() && (lpSetHookWnd != NULL) ) lpSetHookWnd(Handle); } void __fastcall TKeyCapForm::DestroyWindowHandle(void) { TForm::DestroyWindowHandle(); if( lpSetHookWnd != NULL ) lpSetHookWnd(NULL); } void __fastcall TKeyCapForm::OnSystemKeyStroke(TMEssage &Message) { // return 0 to allow Windows to finish processing the key // or return non-zero to prevent further processing /* if( Message.LParam == VK_SNAPSHOT ) { // Print Screen key caught, do something Message.Result = 1; } */ // Add a line to the Memo. Out->Lines->Add("Key: " + AnsiString(Message.WParam) + ", Flags: " + AnsiString(Message.LParam)); Message.Result = 0; } --- KeyCap_DLL.h --- #ifndef KeyCapDLLH #define KeyCapDLLH #define WM_SYSKEYSTROKE (WM_USER + 100) #ifdef BUILDING_DLL #define EXPORT __declspec(dllexport) #else #define EXPORT __declspec(dllimport) #endif #ifdef __cplusplus extern "C" { #endif EXPORT BOOL __stdcall InstallHook(void); EXPORT BOOL __stdcall UninstallHook(void); EXPORT void __stdcall SetHookWnd(HWND hwnd); EXPORT LRESULT CALLBACK KeyboardProc(int code, WPARAM wParam, LPARAM lParam); typedef BOOL (__stdcall *DLLFunc_InstallHook) (void); typedef BOOL (__stdcall *DLLFunc_InstallHook)(void); ^^^^^^^^^^^ Oops! (Yeah I caught and fixed that :-) Quote: typedef void (__stdcall *DLLFunc_SetHookWnd)(HWND); #ifdef __cplusplus } #endif #endif --- KeyCap_DLL.cpp --- #include <windows.h #pragma hdrstop #define BUILDING_DLL #include "KeyCap_DLL.h" typedef struct { HWND hWnd; HHOOK hHook; } THookInfo, *PHookInfo; HINSTANCE DllInstance = NULL; HANDLE hMapping = NULL; PHookInfo pHookInfo = NULL; int WINAPI DllEntryPoint(HINSTANCE hinst, unsigned long reason, void* lpReserved) { switch( reason ) { case DLL_PROCESS_ATTACH: { DllInstance = hinst; hMapping = CreateFileMapping( INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, 0, sizeof(THookInfo), TEXT("KeyCapHookInfo")); if( hMapping != NULL ) { bool bCreated = (GetLastError() != ERROR_ALREADY_EXISTS); pHookInfo = (PHookInfo) MapViewOfFile( hMapping, FILE_MAP_WRITE, 0, 0, 0); if( pHookInfo != NULL ) { if( bCreated == true ) { pHookInfo->hWnd = NULL; pHookInfo->hHook = NULL; } return 1; } CloseHandle(hMapping); hMapping = NULL; } break; } case DLL_PROCESS_DETACH: { if( pHookInfo ) UnmapViewOfFile(pHookInfo); if( hMapping ) CloseHandle(hMapping); break; } } return 0; } BOOL __stdcall InstallHook(void) { if( pHookInfo->hHook == NULL ) pHookInfo->hHook = SetWindowsHookEx(WH_KEYBOARD, (HOOKPROC)KeyboardProc, DllInstance, 0); return (pHookInfo->hHook != NULL); } BOOL __stdcall UninstallHook(void) { if( pHookInfo->hHook != NULL ) { if( UnhookWindowsHookEx(pHookInfo->hHook) ) pHookInfo->hHook = NULL; } return (pHookInfo->hHook == NULL); } void __stdcall SetHookWnd(HWND hwnd) { pHookInfo->hWnd = hwnd; } LRESULT CALLBACK KeyboardProc(int code, WPARAM wParam, LPARAM lParam) { if( (code == HC_ACTION) && (pHookInfo->hWnd != NULL) ) { int iRet = SendMessage(pHookInfo->hWnd, WM_SYSKEYSTROKE , wParam, lParam); if( iRet != 0 ) return iRet; } return CallNextHookEx(pHookInfo->hHook, code, wParam, lParam); } Gambit Thank Gambit. I used your code but I don't see the event being being triggered in the form. When I close the main window I get an AV (the standard "read of address ..." and it drops me in the dll's cpp file but doesn't show where/what caused it. If I put a break point in the callback function it stops there and as soon as I step is AV's. My code is just as you gave it (fishing out the typing errors, like the double `typedef BOOL (__stdcall *DLLFunc_InstallHook)(void)` above. I even tried including the dll's lib file into the mainform's project (--- I have both the mainform and the dll projects open together as a project group. Not sure if this is the best way to work on both at the same time but it seems to work. ---) I'm using BCB5, on XP SP2, if that help at all. -- Stan Back to top Stan R. Guest Posted: Sat Nov 26, 2005 12:53 am    Post subject: Re: DLL <-> Form communication problem (Gloobal Key hook) Stan R. wrote: Quote: Thank Gambit. I used your code but I don't see the event being being triggered in the form. When I close the main window I get an AV (the standard "read of address ..." and it drops me in the dll's cpp file but doesn't show where/what caused it. If I put a break point in the callback function it stops there and as soon as I step is AV's. My code is just as you gave it (fishing out the typing errors, like the double `typedef BOOL (__stdcall *DLLFunc_InstallHook)(void)` above. I even tried including the dll's lib file into the mainform's project (--- I have both the mainform and the dll projects open together as a project group. Not sure if this is the best way to work on both at the same time but it seems to work. ---) I'm using BCB5, on XP SP2, if that help at all. Ok got some more info. It seems like CreateWindowHandle and DestroyWindowHandle are not getting called for some reason. Look in the docs they seem to have the right signature. CreateWindowHandle isn't being called, and thus, the window handle in the dll isn't being set so the message never gets sent (doesn't make it past the IF statement in the call back.) -- Stan Back to top Stan R. Guest Posted: Sat Nov 26, 2005 1:04 am    Post subject: Re: DLL <-> Form communication problem (Gloobal Key hook) Stan R. wrote: Quote: Stan R. wrote: Thank Gambit. I used your code but I don't see the event being being triggered in the form. When I close the main window I get an AV (the standard "read of address ..." and it drops me in the dll's cpp file but doesn't show where/what caused it. If I put a break point in the callback function it stops there and as soon as I step is AV's. My code is just as you gave it (fishing out the typing errors, like the double `typedef BOOL (__stdcall *DLLFunc_InstallHook)(void)` above. I even tried including the dll's lib file into the mainform's project (--- I have both the mainform and the dll projects open together as a project group. Not sure if this is the best way to work on both at the same time but it seems to work. ---) I'm using BCB5, on XP SP2, if that help at all. Ok got some more info. It seems like CreateWindowHandle and DestroyWindowHandle are not getting called for some reason. Look in the docs they seem to have the right signature. CreateWindowHandle isn't being called, and thus, the window handle in the dll isn't being set so the message never gets sent (doesn't make it past the IF statement in the call back.) Ok what the heck... I put a ShowMessage("CreateWindowHandle"); in that function and when I start the program it shows up, but my break point doesnt BREAK on the function (I tried putting a break on the fuctions heading and anywhere below in its body, but it wont break. I see the blue dots and all, and the break remains red (it doesn't turn green-yellow, so it's a valid break point it seems.) What am I missing here? -- Stan Back to top Thomas Maeder [TeamB] Guest Posted: Sat Nov 26, 2005 8:14 am    Post subject: Re: DLL <-> Form communication problem (Gloobal Key hook) Please direct your browser at http://info.borland.com/newsgroups/ and read the newsgroup guidelines. One of them asks us not to quote entire posts we are following up to; instead, please trim the quotes to the parts relevant for your reply. Thanks! Back to top Rudy Velthuis [TeamB] Guest Posted: Sat Nov 26, 2005 10:55 am    Post subject: Re: DLL <-> Form communication problem (Gloobal Key hook) At 01:46:00, 26.11.2005, Stan R. wrote: Quote: Thank Gambit. I used your code but I don't see the event being being triggered in the form. When I close the main window I get an AV (the standard "read of address ..." and it drops me in the dll's cpp file but doesn't show where/what caused it. If I put a break point in the callback function it stops there and as soon as I step is AV's. My code is just as you gave it (fishing out the typing errors, like the double `typedef BOOL (__stdcall *DLLFunc_InstallHook)(void)` above. I even tried including the dll's lib file into the mainform's project (--- I have both the mainform and the dll projects open together as a project group. Not sure if this is the best way to work on both at the same time but it seems to work. ---) I'm using BCB5, on XP SP2, if that help at all. Please do not overquote. http://blogs.teamb.com/rudyvelthuis/articles/7509.aspx I cancelled your extreme overquote, but quoted your text to make replies still possible. -- Rudy Velthuis [TeamB] http://velthuis.homepage.t-online.de "Tragedy is when I cut my finger. Comedy is when you walk into an open sewer and die." - Mel Brooks Back to top Eckstein C. Guest Posted: Sat Nov 26, 2005 7:31 pm    Post subject: Re: DLL <-> Form communication problem (Gloobal Key hook) Rudy Velthuis [TeamB] wrote: Quote: At 01:46:00, 26.11.2005, Stan R. wrote: Thank Gambit. I used your code but I don't see the event being being triggered in the form. When I close the main window I get an AV (the standard "read of address ..." and it drops me in the dll's cpp file but doesn't show where/what caused it. If I put a break point in the callback function it stops there and as soon as I step is AV's. My code is just as you gave it (fishing out the typing errors, like the double `typedef BOOL (__stdcall *DLLFunc_InstallHook)(void)` above. I even tried including the dll's lib file into the mainform's project (--- I have both the mainform and the dll projects open together as a project group. Not sure if this is the best way to work on both at the same time but it seems to work. ---) I'm using BCB5, on XP SP2, if that help at all. Please do not overquote. http://blogs.teamb.com/rudyvelthuis/articles/7509.aspx I cancelled your extreme overquote, but quoted your text to make replies still possible. Ok, both you and another [TeamB] member posted this same thing, but offered no other help. I see nothing wrong with good guidelines, and posting links to them but it looked like he quoted that code for a reason. He had comments with in the body of that code and thats what his post was about. On top of that, he reposted a combination of his posts, without the code, almost half a day before you posts. I think you both jumped the gun here. I jsut don't want this group to become like microsoft's new groups. Very hard to get good help there. Back to top Remy Lebeau (TeamB) Guest Posted: Mon Nov 28, 2005 6:17 pm    Post subject: Re: DLL <-> Form communication problem (Gloobal Key hook) "Stan R." <none@none> wrote Quote: What I saw happening was, when it would worked, it would seem to trigger twice for each key stroke. I would expect that since the hook is called when the key is pressed down as well as when it is released. The lParam value contains several flags that tell you exactly what the key is actually doing at the time the hook is called. Quote: It seemed to stop working when my main form window lost focus Your hook was not truely global, so only your app could access it.. You did not set it up properly to work with other applications. Gambit Back to top Remy Lebeau (TeamB) Guest Posted: Mon Nov 28, 2005 6:21 pm    Post subject: Re: DLL <-> Form communication problem (Gloobal Key hook) "Stan R." <none@none> wrote Quote: Ok got some more info. It seems like CreateWindowHandle and DestroyWindowHandle are not getting called for some reason. That is not possible. Those are VCL methods that are directly tied to the form's Handle property. CreateWindowHandle() is the method that is directly responsible for allocating the HWND for that Handle property. The form would not be able to function at all if CreateWindowHandle() were never called. 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