The CreateDefaultFields method calls GetFieldsList to obtain a list of adapter fields for which it needs to create default child Web items. GetFieldsList obtains a list of the names of its fields from the adapter, and adds them to the specified string list. For any field that is a "default" field (as defined by the adapter), the string in the list is associated with the class of the child Web item that generates a control to represent that field. 

List is a string list to fill with the names of (and Web item classes for) the adapter's default fields. 

CreateDefaultFields 

Adapter