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
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http://www-ist.massey.ac.nz/moretti mailto:G.Moretti@;massey.ac.nz
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