getRow abstract method

Called to obtain the data about a particular row.

Rows should be keyed so that state can be maintained when the data source is sorted (e.g. in response to DataColumn.onSort). Keys should be consistent for a given DataRow regardless of the sort order (i.e. the key represents the data's identity, not the row position).

The DataRow.byIndex constructor provides a convenient way to construct DataRow objects for this method's purposes without having to worry about independently keying each row. The index passed to that constructor is the index of the underlying data, which is different than the index parameter for getRow, which represents the sorted position.

If the given index does not correspond to a row, or if no data is yet available for a row, then return null. The row will be left blank and a loading indicator will be displayed over the table. Once data is available or once it is firmly established that the row index in question is beyond the end of the table, call notifyListeners. (See rowCount.)

If the underlying data changes, call notifyListeners.