type
  TMyComboBox = class(TComboBox)
  published
    property OnMouseDown;
    property OnMouseUp;
    property OnMouseMove;
  end;

type
  TForm1 = class(TForm)
    ComboBox1: TComboBox;
    procedure FormCreate(Sender: TObject);
  private
    procedure DoMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
  public
    { Public declarations }
  end;    var
  Form1: TForm1;    implementation    {$R *.DFM}    procedure TForm1.FormCreate(Sender: TObject);
begin
  TEdit(ComboBox1).OnMouseDown := DoMouseDown;
end;    procedure TForm1.DoMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin    end;