type
  TInputField = class(TCustomControl)
  private
    procedure WMGetDlgCode(var Msg: TWMGetDlgCode); message WM_GETDLGCODE;
  protected
    procedure Paint; override;
    procedure KeyDown(var Key: Word; Shift: TShiftState); override;
    procedure MouseDown(Button: TMouseButton; Shift: TShiftState; X, Y: Integer); override;
  public
    constructor Create(AOwner: TComponent); override;
  end;

implementation

{ TInputField }

constructor TInputField.Create(AOwner: TComponent);
begin
  inherited;
  TabStop := True;
end;

procedure TInputField.WMGetDlgCode(var Msg: TWMGetDlgCode);
begin
  inherited;
  Msg.Result := Msg.Result or DLGC_WANTCHARS or DLGC_WANTARROWS or DLGC_WANTTAB or DLGC_WANTALLKEYS;
end;

procedure TInputField.Paint;
begin
  inherited;
  Canvas.Rectangle(ClientRect);
end;

procedure TInputField.KeyDown(var Key: Word; Shift: TShiftState);
begin
  inherited;
  if Key = VK_RETURN then
    ShowMessage('VK_RETURN');
end;

procedure TInputField.MouseDown(Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
  inherited;
  if CanFocus Then
    SetFocus;
end;