delphi string类型转integer时出错的检测

procedure TForm1.Button1Click(Sender: TObject);
Var
  Num: Integer;
Begin
  Try
    Num:=StrToInt(Edit1.Text);
    Edit2.Text:=IntToStr(Num*Num);
  Except
    On EConvertError Do   ShowMessage(Edit1.Text+'无法转成整数!');
  End;
end;