BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Subclassing WndProc and CM_RECREATEWND          BorlandTalk.com Forum Index -> C++ Builder (VCL Components Usage) View previous topic :: View next topic   Author Message JD Guest Posted: Fri Apr 14, 2006 11:03 pm    Post subject: Subclassing WndProc and CM_RECREATEWND I'm subclassing the WndProc for a TListView's Header: HWND hHandle; FARPROC NewHeaderWndProc; FARPROC OldHeaderWndProc; void __fastcall HeaderWndProc( TMessage &Message ); hHandle = reinterpret_cast<HWND>( ::SendMessage(ListView1->Handle, LVM_GETHEADER, 0, 0) ); NewHeaderWndProc = reinterpret_cast<FARPROC>( MakeObjectInstance(HeaderWndProc) ); OldHeaderWndProc = reinterpret_cast<FARPROC>( ::SetWindowLong(hHandle, GWL_WNDPROC, reinterpret_cast<LONG>(NewHeaderWndProc)) ); My questions are about how to handle if and when the HWND is ever recreated. Do I simply just make another call to SetWindowLong as I did above? Will the Header be sent CM_RECREATEWND as well as the ListView? ~ JD Back to top Remy Lebeau (TeamB) Guest Posted: Sat Apr 15, 2006 12:03 am    Post subject: Re: Subclassing WndProc and CM_RECREATEWND "JD" <nospam (AT) nospam (DOT) com> wrote in message news:44402056$1 (AT) newsgroups (DOT) borland.com... Quote: Will the Header be sent CM_RECREATEWND as well as the ListView? No, because the header is not mananged by the VCL at all. It is managed only by the Win32 API directly, as an internal child of the ListView window. If the ListView HWND is created, it will automatically free the header window as well. You have to catch the CM_RECREATEWND message by subclassing the TListView itself instead. Gambit Back to top JD Guest Posted: Sat Apr 15, 2006 3:03 am    Post subject: Re: Subclassing WndProc and CM_RECREATEWND "Remy Lebeau \(TeamB\)" <no.spam (AT) no (DOT) spam.com> wrote: Quote: [...] If the ListView HWND is created, it will automatically free the header window as well. You have to catch the CM_RECREATEWND message by subclassing the TListView itself instead. I can't get the logic down. At what point do I need to restore the Header's WndProc and then when can I subclass it again? ~ JD Back to top JD Guest Posted: Sat Apr 15, 2006 9:03 am    Post subject: Re: Subclassing WndProc and CM_RECREATEWND "JD" <nospam (AT) nospam (DOT) com> wrote: Quote: I can't get the logic down. [...] This is what I did. Are there any problems with it? //------------------------------------------------------------- void __fastcall TForm1::HeaderWndProc( TMessage &Message ) { if( Message.Msg == WM_DESTROY ) { ::SetWindowLong( hHeader, GWL_WNDPROC, reinterpret_cast<LONG>(OldHeaderWndProc) ); FreeObjectInstance( NewHeaderWndProc ); } Message.Result = ::CallWindowProc( OldHeaderWndProc, hHeader, Message.Msg, Message.WParam, Message.LParam ); } //------------------------------------------------------------- void __fastcall TForm1::NewListViewWndProc( TMessage &Message ) { if( Message.Msg == WM_DESTROY ) { Destroying = true; ListView1->WindowProc = OldListViewWndProc; } else if( Message.Msg == CM_RECREATEWND ) { hHeader = reinterpret_cast<HWND>( ::SendMessage(ListView1->Handle, LVM_GETHEADER, 0, 0) ); NewHeaderWndProc = reinterpret_cast<FARPROC>( MakeObjectInstance(HeaderWndProc) ); OldHeaderWndProc = reinterpret_cast<FARPROC>( ::SetWindowLong(hHeader, GWL_WNDPROC, reinterpret_cast<LONG>(NewHeaderWndProc)) ); } OldListViewWndProc( Message ); } //------------------------------------------------------------- ~ JD Back to top Remy Lebeau (TeamB) Guest Posted: Mon Apr 17, 2006 7:03 pm    Post subject: Re: Subclassing WndProc and CM_RECREATEWND "JD" <nospam (AT) nospam (DOT) com> wrote in message news:4440aed4$1 (AT) newsgroups (DOT) borland.com... Quote: This is what I did. Are there any problems with it? Yes. Your handling of the CM_RECREATEWND message is wrong. You need to pass the CM_RECREATEWND message to the default handler *before* you can subclass the new header HWND. It is during TListView's default handling of that message that the current HWNDs get destroyed and reallocated. You are calling the default handler *after* subclassing the header HWND, so you are going to subclass the HWND that you already subclassed (and thus lose your pointer to the original window procedure) and ignore the new HWND completely. Try this instead: #ifdef STRICT #define MYWNDPROC WNDPROC #else #define MYWNDPROC FARPROC #endif class TForm1 : public TForm { private: HWND hHeader; LONG HeaderWndProcPtr; MYWNDPROC OldHeaderWndProc; TWndMethod OldListViewWndProc; void __fastcall HeaderWndProc(TMessage &Message); void __fastcall ListViewWndProc(TMessage &Message); //... }; __fastcall TForm1::TForm1(TComponent *Owner) : TForm(Owner) { HeaderWndProcPtr = reinterpret_cast<LONG>(MakeObjectInstance(HeaderWndProc)); OldListViewWndProc = ListView1->WindowProc; ListView1->WindowProc = ListViewWndProc; } __fastcall TForm1::~TForm1() { if( hHeader ) { ::SetWindowLong(hHeader, GWL_WNDPROC, reinterpret_cast<LONG>(OldHeaderWndProc)); hHeader = NULL; } ListView1->WindowProc = OldListViewWndProc; FreeObjectInstance(reinterpret_cast<void*>(HeaderWndProcPtr)); } void __fastcall TForm1::HeaderWndProc(TMessage &Message) { Message.Result = ::CallWindowProc(OldHeaderWndProc, hHeader, Message.Msg, Message.WParam, Message.LParam); if( Message.Msg == WM_DESTROY ) { ::SetWindowLong(hHeader, GWL_WNDPROC, reinterpret_cast<LONG>(OldHeaderWndProc)); hHeader = NULL; } } void __fastcall TForm1::ListViewWndProc(TMessage &Message) { OldListViewWndProc(Message); if( Message.Msg == CM_RECREATEWND ) { hHeader = ListView_GetHeader(ListView1->Handle); if( hHeader ) OldHeaderWndProc = reinterpret_cast<MYWNDPROC>(::SetWindowLong(hHeader, GWL_WNDPROC, HeaderWndProcPtr)); } } Gambit Back to top JD Guest Posted: Tue Apr 18, 2006 5:03 am    Post subject: Re: Subclassing WndProc and CM_RECREATEWND "Remy Lebeau \(TeamB\)" <no.spam (AT) no (DOT) spam.com> wrote: Quote: Your handling of the CM_RECREATEWND message is wrong. You need to pass the CM_RECREATEWND message to the default handler *before* you can subclass the new header HWND. [...] Makes perfect sense now! 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