//H  File
bool __fastcall AppHookFunc(TMessage &Message);

//cpp file

void __fastcall TForm2::FormCreate(TObject *Sender)

{

    Application->HookMainWindow(this->AppHookFunc);

}

// ---------------------------------------------------------------------------

void __fastcall TForm2::FormClose(TObject *Sender, TCloseAction &Action)

{

    Application->UnhookMainWindow(this->AppHookFunc);

}

bool __fastcall TForm2::AppHookFunc(TMessage &Message)

{

    bool Handled;

    switch (Message.Msg)

    {

    case WM_CLOSE:

        mrYes == MessageDlg("Really Close??",

            mtWarning,

            TMsgDlgButtons() << mbYes << mbNo,

            ) ? Handled = false : Handled = true;

        break;

    }

    return Handled;

}