Hook: Mouse working only in your application  

Send By: Radikal (Q3 Team)
Web : http://www.q3.nu
Email: radikal@q3.nu
Date: 26/03/00

Tip accessed 574 times

 


I suppose that to somebody it will be he useful this trick.
Have I outlined it to me as a simple exercise of those that you tell yourself to yourself ' that would happen if? '.
It is that the mouse only works in your application. Neither in the Windows desktop, neither in the window's taskbar, neither in any other place that in your form...
Of course, care with him... if you are happened to print something and the driver of your printer it jumps you with the typical message ' papaer empty' you won't be able to close the dialogue that it appears... in short, better you prove it and you see if it is good you for something:

This tip is based on the tip:

[414] - Hooks: Mouse hook at system level

so I don't explain the general operation of hook again, only to say that what changes in this trick is the procedure CallBack of the Hook that will allow to pass the messages in function that the addressee of the same ones is or not our form.
This function has this aspect:


 function CallBackDelHook( Code    : Integer;
                           wParam  : WPARAM;
                           lParam  : LPARAM
                           )       : LRESULT; stdcall;

 var
   DatosMouse     : PMouseHookStruct;
   Intentos       : integer;

 {Esta es la funcion CallBack a la cual llamará el hook.}
 {This is the CallBack function called by he Hook}
 begin
  {Si hay un nuevo evento de raton...}
  {if there is a new mouse event...}
  if code=HC_ACTION then
  begin
   {Miramos si existe el fichero}
   {if the mapfile exists}
   FicheroM:=OpenFileMapping(FILE_MAP_READ,False,'ElReceptor');
   {Si no existe, no enviamos nada a la aplicacion receptora}
   {If dont, send nothing to receiver application}
   if FicheroM<>0 then
   begin
     Compartido:=MapViewOfFile(FicheroM,FILE_MAP_READ,0,0,0);

     {Apuntamos hacia los datos del evento del raton}
     DatosMouse:=Pointer(lparam);

     UnmapViewOfFile(Compartido);
     CloseHandle(FicheroM);
   end;
  end;
  {Llamamos al siguiente hook de la cadena}
  {call to next hook of the chain}
  if Compartido^ <> DatosMouse^.hwnd
    then Result:=1
    else Result:=CallNextHookEx(HookDeMouse, Code, wParam, lParam);
 end;



and the relevant part is this:

  if Compartido^ <> DatosMouse^.hwnd
    then Result:=1
    else Result:=CallNextHookEx(HookDeMouse, Code, wParam, lParam);



that is to say, if the recipient of the message that has captured the hook is our application, we call to the following mouse hook that has installed in the chain, if it is not this way, because we give the message like treaty, miscarrying this way his processed later for the application that is...

Well, like in any hook at system level, we will build ourselves first a DLL that is where anger the procedure CallBack of the hook, and then an example application that will communicate somehow with the DLL.
Therefore:


Hook's DLL



 library HookMouse;

 {Demo de Hook de Ratón a nivel de sistema, Radikal.}

 uses Windows, Messages;

 type
  PCompartido   =^THandle;


 var
  HookDeMouse  : HHook;
  FicheroM     : THandle;
  Compartido   : PCompartido;


 function CallBackDelHook( Code    : Integer;
                           wParam  : WPARAM;
                           lParam  : LPARAM
                           )       : LRESULT; stdcall;

 var
   DatosMouse     : PMouseHookStruct;
   Intentos       : integer;

 {Esta es la funcion CallBack a la cual llamará el hook.}
 {This is the CallBack function called by he Hook}
 begin
  {Si hay un nuevo evento de raton...}
  {if there is a new mouse event...}
  if code=HC_ACTION then
  begin
   {Miramos si existe el fichero}
   {if the mapfile exists}
   FicheroM:=OpenFileMapping(FILE_MAP_READ,False,'ElReceptor');
   {Si no existe, no enviamos nada a la aplicacion receptora}
   {If dont, send nothing to receiver application}
   if FicheroM<>0 then
   begin
     Compartido:=MapViewOfFile(FicheroM,FILE_MAP_READ,0,0,0);

     {Apuntamos hacia los datos del evento del raton}
     DatosMouse:=Pointer(lparam);

     UnmapViewOfFile(Compartido);
     CloseHandle(FicheroM);
   end;
  end;
  {Llamamos al siguiente hook de la cadena}
  {call to next hook of the chain}
  if Compartido^ <> DatosMouse^.hwnd
    then Result:=1
    else Result:=CallNextHookEx(HookDeMouse, Code, wParam, lParam);
 end;

 procedure HookOn; stdcall;
 {Procedure que instala el hook}
 {procedure for install the hook}
 begin
   HookDeMouse:=SetWindowsHookEx(WH_MOUSE, @CallBackDelHook, HInstance , 0);
 end;

 // stops this type of watch
 procedure HookOff;  stdcall;
 begin
 {procedure para desinstalar el hook}
 {procedure to uninstall the hook}
   UnhookWindowsHookEx(HookDeMouse);
 end;

 exports
 {Exportamos las procedures...}
 {Export the procedures}
  HookOn,
  HookOff;

 begin
 end.




Demo application



In a clean form, put this code un its unit:


 unit Unit1;

 interface

 uses
   Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
   StdCtrls, ExtCtrls;

 const
   NombreDLL       = 'HookMouse.dll';

 type
  PCompartido   =^THandle;
  THookMouse=procedure; stdcall;

 type
   TForm1 = class(TForm)
     procedure FormCreate(Sender: TObject);
     procedure FormDestroy(Sender: TObject);
   private
     { Private declarations }
     FicheroM       : THandle;
     Compartido     : PCompartido;
     HandleDLL      : THandle;
     HookOn,
     HookOff        : THookMouse;

   public
     { Public declarations }
   end;

 var
   Form1: TForm1;

 implementation

 {$R *.DFM}

 procedure TForm1.FormCreate(Sender: TObject);
 begin
   HandleDLL:=LoadLibrary( PChar(ExtractFilePath(Application.Exename)+
                                 NombreDLL ) );
   if HandleDLL = 0 then raise Exception.Create('No se pudo cargar la DLL');

   @HookOn :=GetProcAddress(HandleDLL, 'HookOn');
   @HookOff:=GetProcAddress(HandleDLL, 'HookOff');

   IF not assigned(HookOn) or
      not assigned(HookOff)  then
      raise Exception.Create('No se encontraron las funciones en la DLL'+#13+
                             'Cannot find the required DLL functions');

   {Creamos el fichero de memoria}
   FicheroM:=CreateFileMapping( $FFFFFFFF,
                               nil,
                               PAGE_READWRITE,
                               0,
                               SizeOf(THandle),
                               'ElReceptor');

    {Si no se creó el fichero, error}
    if FicheroM=0 then
      raise Exception.Create( 'Error al crear el fichero'+
                              '/Error while create file');

    {Direccionamos nuestra estructura al fichero de memoria}
    Compartido:=MapViewOfFile(FicheroM,FILE_MAP_WRITE,0,0,0);

    {Escribimos datos en el fichero de memoria}
    Compartido^:=Handle;
    HookOn;
 end;

 procedure TForm1.FormDestroy(Sender: TObject);
 begin
  {Desactivamos el Hook}
  {Uninstall the Hook}
  if Assigned(HookOff) then HookOff;

  {Liberamos la DLL}
  {Free the DLL}
  if HandleDLL<>0 then
   FreeLibrary(HandleDLL);

  {Cerramos la vista del fichero y el fichero}
  {Close the memfile and the View}
  if FicheroM<>0 then
  begin
    UnmapViewOfFile(Compartido);
    CloseHandle(FicheroM);
  end;
 end;


 end.



Note: If you use this technique in an application with several forms, you will put in ' Compartido' the handle of the form that you will activate, but it won't receive mouse events. For example, you can make it in the event OnShow of the form...