如何自制控件

unit edtCardID;interfaceuses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;type
  TedtCardID = class(TEdit)
  private
    { Private declarations }
  protected
    procedure  KeyPress(var Key:char);override;
    procedure  DoExit;override;
    procedure  Loaded;override;
   public
    constructor Create(AOwner: TComponent); override;  published
    { Published declarations }
  end;procedure Register;implementationprocedure Register;
begin
  RegisterComponents('JBC', [TedtCardID]);
end;
constructor TedtCardID.Create(AOwner: TComponent);
begin
  inherited  Create(AOwner);
  MaxLength:=6;
end;
procedure TedtCardID.KeyPress(var Key:char);
begin
  Inherited;
  if (Key>'9') or (Key in ['!'..'/']) then
  begin
    Key:=#0;
  end;
end;
procedure TedtCardID.DoExit;
var
  i:integer;
begin
  Inherited;
  if Trim(Text)='' then
    Exit;
  For i := Length(Text)+1 to 6 do
    Text := '0' + Text;
end;
procedure TedtCardID.Loaded;
begin
  inherited Loaded;
  SetWindowText(Handle, '')
end;end.