Use the Excel Export API to Create Shared Formulas

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A shared formula consists of a formula in one cell marked as shared and the cells referenced by the shared formula. The referenced cells obtain their own version of the formula, so if cell D2 has the formula B2*C2, then cell D3 would have the formula B3*C3 etc.

It takes two steps to build a shared formula. First, add a formula to the first cell in a range - it is the host formula. Next, add a reference to the host formula to any other cell of the range. The IXlCell.SetSharedFormula method with different parameters serves both steps, as illustrated in the code below.

// Create data rows.
for (int i = 0; i < 4; i++) {
    using (IXlRow row = sheet.CreateRow()) {
        using (IXlCell cell = row.CreateCell()) {
            cell.Value = product[i];
        }
        using (IXlCell cell = row.CreateCell()) {
            cell.Value = qty[i];
        }
        using (IXlCell cell = row.CreateCell()) {
            cell.Value = price[i];
        }
        using (IXlCell cell = row.CreateCell()) {
            // Use the shared formula to calculate the amount per product. 
            if (i == 0)
                cell.SetSharedFormula("B2*C2", XlCellRange.FromLTRB(3, 1, 3, 4));
            else
                cell.SetSharedFormula(new XlCellPosition(3, 1));
        }
    }
}