private void LayerNameCB_SelectionChanged(object sender, SelectionChangedEventArgs e)
 {
     selectedLayerName    = e.AddedItems[0].ToString();
     _fieldNames          = _mapMgr.GetFieldNames(selectedLayerName);
     FieldsLB.ItemsSource = _fieldNames;
     SelectClauseTB.Text  = "SELECT * FROM " + selectedLayerName + " WHERE: ";
 }