void OnOpen(object sender, EventArgs e)
        {
            if (String.IsNullOrEmpty(txtPath.Text))
            {
                return;
            }
            IShellService shell = GlobalServices.Instance.GetService <IShellService>();

            if (shell != null)
            {
                shell.OpenFile(txtPath.Text, btnOpen);
            }
            else
            {
                DisplayAlert("GridDemo", "Unable to open a file. The Shell service is not found.", "Cancel");
            }
        }