TActiveTableRowEventParameter class.
The TActiveTableRowEventParameter provides the parameter passed during the callback requestion in the CallbackParameter property. The callback response content (e.g. new HTML content) must be rendered using an THtmlWriter obtained from the NewWriter property, which returns a NEW instance of TCallbackResponseWriter.
The SelectedRowIndex is a zero-based index of the TActiveTableRow , -1 if the row is not part of the row collection (this shouldn't happen though since an exception is thrown before).