C# Excel cell validation to only accept int values

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C#

Hi all
I am struggling to get some cell validation working. I have been passed over code which needs some improvements. Currently I need cells to only accept a int value, but users currently can enter apostrophes into the cell which then later causes problems.

The Excel sheets are all generated programmatically and comments are sparse. I believe the leafcells are where the user will enter the data, sorry can't provide an example

what I have is

public void WriteRowsBody(xl::Worksheet sheet, IEnumerable<ServiceAgreement> agreements, ref int lastRow)
       {
           // Initialise the row & cell counters for the data.
           xl::Range range = null;
           Cell[] leafcells = Cells.SelectMany(c => c.Leaves).ToArray();
           int col = 1;
           int row = lastRow + 1;

           foreach (ServiceAgreement sa in agreements)
           {
               // Write the first batch of data.
               string[] values = new string[] { sa.Id, (sa.DateWeekStart.HasValue ? sa.DateWeekStart.Value.ToString("yyyy-MM-dd") : ""), sa.ClientName, sa.ClientAddress, sa.ServiceElement };
               for (int i = 0; i < values.Length; i++, col++)
               {
                   sheet.Cells[row, col].Value2 = values[i];
                   sheet.Range[sheet.Cells[row, col], sheet.Cells[row + 1, col]].Merge();

               }
               sheet.Cells[row, col].Value2 = "Planned";
               sheet.Cells[row + 1, col].Value2 = "Actual";
               // Write the data cells.
               WriteDataCells(sheet, sa, row);

               // Set the default formatting for the data rows.
               range = sheet.Range[sheet.Cells[row, 1], sheet.Cells[row + 1, leafcells.Length]];

               XlPaintBackground(range, TitleColour);

               XlSetAlignment(range, xl::XlHAlign.xlHAlignCenter, xl::XlVAlign.xlVAlignCenter);

               // Set the specific formatting for the data rows.
               for (int i = 0; i < leafcells.Length; i++)
               {
                   XlDrawBorder(sheet.Cells[row, i + 1], Color.Black);
                   xl::Range rb = sheet.Cells[row + 1, i + 1];
                   XlDrawBorder(rb, Color.Black);
                   //Makes the leaf cells editable
                   if (leafcells[i].IsEditable)
                   {
                       //sets the color of the editable leaf cells to white
                       XlPaintBackground(rb, alternate);
                       XlProtect(rb, false);

                   }


               }

               col = 1;
               row += 2;
           }

           lastRow = row;

       }

How do I go about validating the cells?

Any help please
:)
Thanks