Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

{ 
Question: 
  What is the most easy way to set a same font name to all controls 
  in project in run time? 

Answer: 
  By default all controls have ParentFont = true, so if you did not change 
  that  for specific controls you could just change the forms Font 
  property, e.g. in code attached to the Screen.OnActiveFormChange event. 
  If you cannot rely on all controls having Parentfont = true you would 
  have to loop over all controls on the form and set the font property for 
  each or at least for those that have ParentFont set to false. You can 
  use the routines from unit TypInfo for that, they allow you to access 
  published properties by name. The code, again sitting in a handler for 
  Screen.onActiveFormChange, would be something like this: 

  ModifyFontsFor( Screen.ActiveControl ); 

where 
}

 procedure ModifyFontsFor(ctrl: TWinControl);
   procedure ModifyFont(ctrl: TControl);
   var
     f: TFont;
   begin
     if IsPublishedProp(ctrl, 'Parentfont')
       and (GetOrdProp(ctrl, 'Parentfont') = Ord(false))
       and IsPublishedProp(ctrl, 'font')
       then begin
       f := TFont(GetObjectProp(ctrl, 'font', TFont));
       f.Name := 'Symbol';
     end;
   end;
 var
   i: Integer;
 begin
   ModifyFont(ctrl);
   for i := 0 to ctrl.controlcount - 1 do
     if ctrl.controls[i] is Twincontrol then
       ModifyFontsfor(TWincontrol(ctrl.controls[i]))
     else
       Modifyfont(ctrl.controls[i]);
 end;

 procedure TForm1.Button2Click(Sender: TObject);
 begin
   Modifyfontsfor(self);
 end;

 // Remember to add TypInfo to your uses clause.