| Data Access Modes > User Events Mode > Defining Fields for User Events Mode |
As with memory array mode, there is no data source to supply field information, so when in user events mode you must define the fields that make up the structure of the custom data source. You can specify the Fields collection either at design time on the Fields property page, or at run time in the WillOpenData event.
Each data field corresponds to a column in a RowBuffer object passed to the UserReadData, UserWriteData, and UserAddData events. The order of the fields determines the zero-based column index that corresponds to a particular data field.
Only data fields are present in the RowBuffer object, not calculated fields.
When defining fields in user events mode, the most important properties are Name, which specifies the field name exposed to bound controls, and Type, which determines the variant subtype that will be used when data is copied to a RowBuffer object. For more information, see Field properties.