private void EhUseSelectedItemAsVColumns() { foreach (var node in _availableColumns.Where(n => n.IsSelected)) { var colToAdd = node.Tag as IReadableColumn; if (colToAdd == null) { continue; } // before adding this node, check that it is not already present var proxyToAdd = ReadableColumnProxyBase.FromColumn(colToAdd); if (_valueColumns.Any(n => proxyToAdd.DocumentPath.Equals(((IReadableColumnProxy)n.Tag).DocumentPath))) { continue; } _valueColumns.Add(new SelectableListNode(colToAdd.FullName, proxyToAdd, false)); } }