private void OnToolbarClick(object sender, ToolbarButtonClickEventArgs e)
        {
            switch (e.ClickedButton)
            {
            case ToolbarButton.New:
                NewCommand?.TryExecute();
                break;

            case ToolbarButton.Delete:
                DeleteCommand?.TryExecute();
                break;

            case ToolbarButton.Select:
                StartSelectionCommand?.TryExecute();
                break;

            case ToolbarButton.Refresh:
                RefreshCommand?.TryExecute();
                break;

            case ToolbarButton.Cancel:
                CancelSelectionCommand?.TryExecute();
                break;
            }
        }