Kyley I did put '' around correct for a reason :-)
Neven ----- Original Message ----- From: "Kyley Harris" <[EMAIL PROTECTED]> To: "Multiple recipients of list delphi" <[EMAIL PROTECTED]> Sent: Wednesday, October 23, 2002 10:15 PM Subject: RE: [DUG]: Polymorphic assignment to Color - How? (sometime it's a Property, sometimes not) > Well I mentioned 'one way' to do it. I guess Neven has mentioned > 'another' way to do it. > > 'correct' is like skinning a cat. It depends on the question asked. > While the interface method is potentially a cleaner way of doing > something in a perfect world where all things are defined > In a nice application Framework where the author has subclassed every > visual control they ever want or might use, VCL or 3rd party to > implement an interface. > > Giovanni's original question implied a generic, I don't want to know > what I'm talking to, only > That it has a property and is already an existing object in an existing > architecture. Therefore correct is a matter of perspective within the > given boundaries of the environment. > > In this case, based on the question, I think RTTI use to replace the one > routine is more 'correct' than recommending refactoring an entire > application of unknown quantity. > > IMHO > > Regards > Kyley > > > > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:owner-delphi@;delphi.org.nz] On > Behalf Of Neven MacEwan > Sent: Wednesday, 23 October 2002 9:12 p.m. > To: Multiple recipients of list delphi > Subject: Re: [DUG]: Polymorphic assignment to Color - How? (sometime > it's a Property, sometimes not) > > > Giovanni > > The 'correct' way would be to implement an interface > > 1/ Declare the interface > > type > IPresentation = interface(IInterface) > procedure SetColor(Value: TColor); > end > > 2/ Implement the IF on your classes > > type > TColorableFrom = class(TForm, IPresentation) > > you then have the option of implementuing the interface or delegating it > to an 'helper' object > > then to use it > > var > PesI: IPresentation; > > if Supports(Instance,IPresentation, PresI) then Pesi.SetColor(Color) > > HTH > > Neven > > > > > ----- Original Message ----- > From: "Moretti, Giovanni" <[EMAIL PROTECTED]> > To: "Multiple recipients of list delphi" <[EMAIL PROTECTED]> > Sent: Wednesday, October 23, 2002 6:23 PM > Subject: [DUG]: Polymorphic assignment to Color - How? (sometime it's a > Property, sometimes not) > > > > Hi > > > > I'm building a list of objects that can be coloured and want to be > > able to > get/set their colour. > > > > The object properties are all going to be stored in a Tlist so the > > types > will probably need to be stored along with them. I'm happy to store the > Object type (eg Tform ...) along with the reference to the object but I > can't see a general way to do this and get/set the color. > > > > ========= ATTEMPT #1 =========================================== > > > > In the olden days, before properties, I'd have just passed a pointer > > to > the Tcolor value: > > > > procedure setObjectColour (Color : ^TColor ; > > newColour : TColor); > > begin > > Color^ := newColour; > > end; > > > > setObjectColour(@Label3.Color, clRed); > > > > I tried this, but it's unpredictable as sometimes an object's color is > just a TColor (a glorified integer) but other times it's a property with > get/set methods. > > > > ========= ATTEMPT #2 =========================================== > > > > Figuring the run-time type information should be able to handle this, > > I > tried: > > > > Type TControlClass = Class of Tcontrol; > > > > procedure setObjectColour ( obj : TObject; > > whatClass : TControlClass; > > newColour : TColor); > > begin > > (obj as whatClass).color := newColour; > > ^-------------- ERROR - COLOR not declared > > // OR > > > > whatClass(object).color := newColour; > > ^----------------------------Missing Operator or ; > > end; > > > > setObjectColour(Label3, Tlabel, clRed); // To Recolour something > > > > But neither will compile without errors. > > > > ========= FINALLY =========================================== > > > > It's not elegant but has the great virtue that it actually works: > > > > procedure setObjectColour ( obj : TObject; > > newColour : TColor); > > begin > > if (obj is TForm) then (obj as TForm) .color := newColour > > else if (obj is TLabel) then (obj as TLabel).color := newColour > > else if (obj is TFont ) then (obj as TFont) .color := newColour > > else if (obj is TBrush) then (obj as TBrush).color := newColour > > else if (obj is TPen) then (obj as TPen) .color := newColour > > else showMessage('setObjectColour: Don''t know how'); > > end; > > > > setObjectColour(Form1, clRed); > > > > Except this means that adding new types of things will require adding > > of > extra "if .." statements which with polymorphism should be necessary. > Unfortunately you can't do the more general: > > > > (obj as Tcontrol).color := newColour; > > > > As Tcontrol's "color" is protected (and can't be seen this won't > > compile). > Only Tcontrol's descendents expose some way of getting/setting color. > > > > I want to be able to recolour anything that has a colour but there > > must be > a better way than tests for explicit types/classes ... > > > > Any Ideas? > > > > Thanks > > Giovanni > > ====================================================================== > > == > > Giovanni Moretti | Institute of Information Sciences and Technology > > Senior Lecturer | Massey University, Palmerston North, New Zealand > > Computer Science | Ph 64-6-3505799x2474 == Fax 64-6-3502259 == > ZL2BOI > > > ------------------------------------------------------------------------ > > http://www-ist.massey.ac.nz/moretti > mailto:G.Moretti@;massey.ac.nz > > > ------------------------------------------------------------------------ > -- > - > > New Zealand Delphi Users group - Delphi List - > [EMAIL PROTECTED] > > Website: http://www.delphi.org.nz > > To UnSub, send email to: [EMAIL PROTECTED] > > with body of "unsubscribe delphi" > > Web Archive at: http://www.mail-archive.com/delphi%40delphi.org.nz/ > > > > ------------------------------------------------------------------------ > --- > New Zealand Delphi Users group - Delphi List - [EMAIL PROTECTED] > Website: http://www.delphi.org.nz > To UnSub, send email to: [EMAIL PROTECTED] > with body of "unsubscribe delphi" > Web Archive at: http://www.mail-archive.com/delphi%40delphi.org.nz/ > > -------------------------------------------------------------------------- - > New Zealand Delphi Users group - Delphi List - [EMAIL PROTECTED] > Website: http://www.delphi.org.nz > To UnSub, send email to: [EMAIL PROTECTED] > with body of "unsubscribe delphi" > Web Archive at: http://www.mail-archive.com/delphi%40delphi.org.nz/ > --------------------------------------------------------------------------- New Zealand Delphi Users group - Delphi List - [EMAIL PROTECTED] Website: http://www.delphi.org.nz To UnSub, send email to: [EMAIL PROTECTED] with body of "unsubscribe delphi" Web Archive at: http://www.mail-archive.com/delphi%40delphi.org.nz/
