void TreeView_BeforeLabelEdit (object sender, NodeLabelEditEventArgs e)
{
string newLabel = e.Label == null ? "null" : e.Label;
_eventsText.AppendText ("TreeView => BeforeLabelEdit (" + e.Node.Text +
" => " + newLabel + ")" + Environment.NewLine);
e.CancelEdit = _beforeCancelCheckBox.Checked;
}