How to change the font color of all components on a form at runtime

Problem/Question/Abstract:

I would like to change the font color on all components on a form at runtime (and the components owned by the components etc). I devised a recursive algorithm using RTTI that accepts a TComponent as a parameter. It works to some extent, but I still have to use 'if' statements to cast the object to a particular descendant, resulting in about 30 lines of code to test for all of the components I use. Also, some objects (TColumnTitle), are not descended from TComponent, even though they have a font property.

Answer:

This may do the trick (with D6 and maybe D5):

uses
  TypInfo;

{ ... }
var
  i: integer;
  aFont: TFont;
begin
  for i := 0 to aComponent.ComponentCount - 1 do
  begin
    aFont := TFont(GetOrdProp(aComponent.Components[i], 'Font'));
    if assigned(aFont) then
      aFont.Color := clWhite;
  end;
end;


With D4:

{ ... }
var
  i: integer;
  aFont: TFont;
  pi: PPropInfo;
begin
  for i := 0 to aComponent.ComponentCount - 1 do
  begin
    pi := GetPropInfo(aComponent.Components[i].ClassInfo, 'Font');
    if assigned(pi) then
      TFont(GetOrdProp(aComponent.Components[i], pi)).Color := clWhite;
  end;
end;