unit Unt_Test;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls,Unt_Error;

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
    a: TMyClass;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
  try
    a.No := StrToInt(Self.Edit1.Text);
  except
    on Err1: MyError do
    begin
      ShowMessage(Err1.ErrorInfo);
    end;
  end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  a := TMyClass.Create;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  FreeAndNil(a);
end;

end.