（TSQLConnection）为什么Left和Top属性仅在.dfm文件中可用？

Question

I'm just curious why you can drop a TSQLConnection on a form and it will add Left and Top properties to the .dfm :

object Form1: TForm1
  ...
  object SQLConnection1: TSQLConnection
    Left = 8
    Top = 8
  end
end

But when you create it in code, the Left and Top properties are not members of the TSQLConnection class:

interface

type
  TForm1 = class(TForm)
    SQLConnection1: TSQLConnection;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
    FSQLCon: TSQLConnection;
  public
    { Public declarations }
  end;

implementation

procedure TForm1.FormCreate(Sender: TObject);
begin
  FSQLCon := TSQLConnection.Create(Self);
  FSQLCon.Left := 280;
  FSQLCon.Top := 200;
end;

Compile:

[DCC Error] Unit1.pas(30): E2003 Undeclared identifier: 'Left'
[DCC Error] Unit1.pas(31): E2003 Undeclared identifier: 'Top'

Why are some properties only available for assignment in the .dfm ? Shouldn't you be able to assign all properties in code ( .pas ) that are set in the form ( .dfm )?

FYI - Using Delphi XE2 (Update 3)

Answer 1

The properties Left and Top for TComponent do not exist really. The are set for the designer in DefineProperties used by ReadProperty and WriteProperties .

Take a look at classes.pas.