Returns the number of rows displayed (that is, rows in the primary buffer) if it succeeds and -1 if it fails. If there is no DataWindow object assigned to the DataWindow control or DataStore, this method returns -1.
Normally, when you call Retrieve, any rows that are already in the DataWindow control or DataStore are discarded and replaced with the retrieved rows. You can return the code 2 in the RetrieveStart event to prevent this. In this case, Retrieve adds any retrieved rows to the ones that already exist in the buffers.