private void askShpFieldNamesValues(string filename, int fieldIndex)
        {
            SchemaDB_shapefiles shp = new SchemaDB_shapefiles(filename, fieldIndex);

            _fieldNames  = shp.FieldNames;
            _fieldValues = shp.FieldValues;
        }
        private void askShpFieldNames(string filename)
        {
            SchemaDB_shapefiles shp = new SchemaDB_shapefiles(filename);

            _fieldNames = shp.FieldNames;
        }