Add dropdown list in the Excel sheet using C#

Question

I am filling the Excel cells as row and column using C# in my entire project as given below. Now there is a new requirement to add a dropdownlist in the particular cell.

Answer 1

First make a list for dropdown

        var list = new System.Collections.Generic.List<string>();
        list.Add("Charlie");
        list.Add("Delta");
        list.Add("Echo");
        var flatList = string.Join(",", list.ToArray());

then add this list as dropdown in the particular cell as below

var cell = (Microsoft.Office.Interop.Excel.Range)oSheet.Cells[row, 8];
            cell.Validation.Delete();
            cell.Validation.Add(
               XlDVType.xlValidateList,
               XlDVAlertStyle.xlValidAlertInformation,
               XlFormatConditionOperator.xlBetween,
               flatList,
               Type.Missing);

            cell.Validation.IgnoreBlank = true;
            cell.Validation.InCellDropdown = true;