BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  OnDrawCell (TStringGrid) requesting constant TRect          BorlandTalk.com Forum Index -> C++ Builder (VCL Components Development) View previous topic :: View next topic   Author Message Erik Doekes Guest Posted: Sun Jul 03, 2005 11:34 am    Post subject: OnDrawCell (TStringGrid) requesting constant TRect Hi! In the help to C++Builder Personal it is stated that the OnDrawCell event has parameters (TObject*, long, long, TRect, TGridDrawState) but when try to run an application with a grid derived from TStringGrid containing an OnDrawCell event it seems that the compiler wants (TObject*, int, int, const TRect &, TGridDrawState) as parameters. Changing long to int doesn't bother me, since I will avoid anyway to have many entries in my lists at the same time. But as I understood the method TCanvas::TextRect right, I will need to modify the TRect passed through to the OnDrawCell event, but maybe I've misunderstood this: -Does TextRect modify the TRect one passes through, or can I make a copy of the TRect passed through to OnDrawCell, modify this copy and then pass it through to TextRect? -And why does the help say something totally different? Is there a method with different parameters to which I haven't got access in my personal edition or is this just a small "bug"? /Erik Back to top Rudy Velthuis [TeamB] Guest Posted: Sun Jul 03, 2005 11:43 am    Post subject: Re: OnDrawCell (TStringGrid) requesting constant TRect At 13:34:13, 03.07.2005, Erik Doekes wrote: Quote: Hi! In the help to C++Builder Personal it is stated that the OnDrawCell event has parameters (TObject*, long, long, TRect, TGridDrawState) but when try to run an application with a grid derived from TStringGrid containing an OnDrawCell event it seems that the compiler wants (TObject*, int, int, const TRect &, TGridDrawState) as parameters. The help I have has this example: << The following code uses the bitmaps in an image list component to draw the contents of each cell in a draw grid. It draws a focus rectangle around the cell that has focus. void __fastcall TForm1::DrawGrid1DrawCell(TObject *Sender, long Col, long Row, TRect &Rect, TGridDrawState State) { long index = Row * DrawGrid1->ColCount + Col; DrawGrid1->Canvas->Brush->Color = clNormalBackground; DrawGrid1->Canvas->FillRect(Rect); ImageList1->Draw(DrawGrid1->Canvas,Rect.Left,Rect.Top,index); if (State.Contains(gdFocused)) DrawGrid1->Canvas->DrawFocusRect(Rect); } Quote: -- Rudy Velthuis [TeamB] http://velthuis.homepage.t-online.de "If it weren't for electricity we'd all be watching television by candlelight." -- George Gobel. Back to top Rudy Velthuis [TeamB] Guest Posted: Sun Jul 03, 2005 12:01 pm    Post subject: Re: OnDrawCell (TStringGrid) requesting constant TRect At 13:43:41, 03.07.2005, Rudy Velthuis [TeamB] wrote: Quote: void __fastcall TForm1::DrawGrid1DrawCell(TObject *Sender, long Col, long Row, TRect &Rect, TGridDrawState State) { long index = Row * DrawGrid1->ColCount + Col; DrawGrid1->Canvas->Brush->Color = clNormalBackground; DrawGrid1->Canvas->FillRect(Rect); ImageList1->Draw(DrawGrid1->Canvas,Rect.Left,Rect.Top,index); if (State.Contains(gdFocused)) DrawGrid1->Canvas->DrawFocusRect(Rect); } I started BCB6, created a new VCL application (File | New | Application), and put a TStringGrid on the form. In the Object Inspector, I selected the Events tab, and double-clicked the empty cell beside OnDrawCell. The IDE added a new member function: //--------------------------------------------------------------------- void __fastcall TForm1::StringGrid1DrawCell(TObject *Sender, int ACol, int ARow, TRect &Rect, TGridDrawState State) { } //--------------------------------------------------------------------- So it is not "const TRect &Rect", just "TRect &Rect", which of course allows you to modify the rect. -- Rudy Velthuis [TeamB] http://velthuis.homepage.t-online.de "A clever man commits no minor blunders." - Goethe (1749-1832) Back to top Erik Doekes Guest Posted: Sun Jul 03, 2005 2:32 pm    Post subject: Re: OnDrawCell (TStringGrid) requesting constant TRect I tried the same and it works as long as I create a StringGrid visually and double-click OnDrawCell (and e.g. put some code there using StringGrid1->Canvas->TextRect(Rect, ...)). But as soon as I in my non-visual class write TRect& instead of const TRect& I get the message "Cannot convert 'void (_fastcall * (_closure )(TObject*,int,int,TRect&,TGridDrawState))(TObject*,int,int,TRect& ,TGridDrawState)' to 'void (_fastcall * (_closure )(TObject*,int,int,const TRect&,TGridDrawState))(TObject*,int,int,const TRect&,TGridDrawState)'." What can this depend on? /Erik Quote: I started BCB6, created a new VCL application (File | New | Application), and put a TStringGrid on the form. In the Object Inspector, I selected the Events tab, and double-clicked the empty cell beside OnDrawCell. The IDE added a new member function: //--------------------------------------------------------------------- void __fastcall TForm1::StringGrid1DrawCell(TObject *Sender, int ACol, int ARow, TRect &Rect, TGridDrawState State) { } //--------------------------------------------------------------------- So it is not "const TRect &Rect", just "TRect &Rect", which of course allows you to modify the rect. -- Rudy Velthuis [TeamB] http://velthuis.homepage.t-online.de "A clever man commits no minor blunders." - Goethe (1749-1832) Back to top Rudy Velthuis [TeamB] Guest Posted: Sun Jul 03, 2005 2:48 pm    Post subject: Re: OnDrawCell (TStringGrid) requesting constant TRect At 16:32:52, 03.07.2005, Erik Doekes wrote: Quote: I tried the same and it works as long as I create a StringGrid visually and double-click OnDrawCell (and e.g. put some code there using StringGrid1->Canvas->TextRect(Rect, ...)). But as soon as I in my non-visual class write TRect& instead of const TRect& I get the message "Cannot convert 'void (_fastcall * (_closure )(TObject*,int,int,TRect&,TGridDrawState))(TObject*,int,int,TRect& ,TGridDrawState)' to 'void (_fastcall * (_closure )(TObject*,int,int,const TRect&,TGridDrawState))(TObject*,int,int,const TRect&,TGridDrawState)'." What can this depend on? Probably on the include file. Problem is, that the include file has: typedef void __fastcall (__closure *TDrawCellEvent) (System::TObject* Sender, int ACol, int ARow, const Types::TRect &Rect, TGridDrawState State); This is a correct translation of the original Delphi code: TDrawCellEvent = procedure (Sender: TObject; ACol, ARow: Longint; Rect: TRect; State: TGridDrawState) of object; So it seems a Delphi user won't be able to modify the rect either (it is passed with value semantics, but in reality -- due to how the Delphi compiler codes such calls -- passed as a reference), so const TRect& Rect is correct after all. It seems the IDE creates the wrong stub. I have no idea why. -- Rudy Velthuis [TeamB] http://velthuis.homepage.t-online.de "Good people do not need laws to tell them to act responsibly, while bad people will find a way around the laws." - Plato (427-347 B.C.) Back to top Remy Lebeau (TeamB) Guest Posted: Sun Jul 03, 2005 6:21 pm    Post subject: Re: OnDrawCell (TStringGrid) requesting constant TRect "Erik Doekes" <erdo8113 (AT) student (DOT) uu.se> wrote Quote: In the help to C++Builder Personal it is stated that the OnDrawCell event has parameters (TObject*, long, long, TRect, TGridDrawState) but when try to run an application with a grid derived from TStringGrid containing an OnDrawCell event it seems that the compiler wants (TObject*, int, int, const TRect &, TGridDrawState) as parameters. Like most of the other examples in the help file, the function/event signatures listed in the help file are just literal C++ translations (probably human made rather than machine made) of the Delphi Pascal source code that the VCL is written in. As such, the help file does not always match what the compiler actually expects. In Delphi, the signature of the OnDrawCell event is: (TObject, Longint, Longint, TRect, TGridDrawState) Which is what you see in the help file. But when passing class instances as function parameters in C++, it is more efficient to pass them by const reference instead of by value, so the Pascal-to-C++ convertor that BCB implies to general HPP header files for the VCL uses const references, which is what you are seeing the compiler expecting. Quote: But as I understood the method TCanvas::TextRect right, I will need to modify the TRect passed through to the OnDrawCell event, but maybe I've misunderstood this: Where did you get that idea from? Quote: -Does TextRect modify the TRect one passes through No. TextRect() also expects a const reference as well. Quote: or can I make a copy of the TRect passed through to OnDrawCell, modify this copy and then pass it through to TextRect? Yes. Or you can pass the original TRect directly, if you do not need to actually change the TRect's values. Quote: -And why does the help say something totally different? See above. Quote: Is there a method with different parameters to which I haven't got access in my personal edition or is this just a small "bug"? It is a documentation error, not an IDE/compiler bug. Borland's documentation has never been as good as it should be. Gambit Back to top Erik Doekes Guest Posted: Sun Jul 03, 2005 8:55 pm    Post subject: Re: OnDrawCell (TStringGrid) requesting constant TRect Quote: Is there a method with different parameters to which I haven't got access in my personal edition or is this just a small "bug"? It is a documentation error, not an IDE/compiler bug. Borland's documentation has never been as good as it should be. That's actually what I meant with "bug", that's why I used quotation marks, but maybe that is abuse of the word "bug". Well, I'm quite satisfied with Borland's documentation/help over all. I think they are in the top league anyway concerning documentation, I've seen a lot worse... 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