次のサンプルコードは、SelectorIndexプロパティを設定します。
FarPoint.Win.Spread.RowHeader r;
r = fpSpread1.ActiveSheet.RowHeader;
r.ColumnCount = 4;
r.SelectorIndex = 2;
fpSpread1.Sheets[0].ShowRowSelector = true;
Dim r As FarPoint.Win.Spread.RowHeader
r = FpSpread1.ActiveSheet.RowHeader
r.ColumnCount = 4
r.SelectorIndex = 2
FpSpread1.Sheets(0).ShowRowSelector = True