Worksheet Class

[ChildElementInfoAttribute(typeof(WorksheetExtensionList))]
[ChildElementInfoAttribute(typeof(Hyperlinks))]
[ChildElementInfoAttribute(typeof(TableParts))]
[ChildElementInfoAttribute(typeof(SheetDimension))]
[ChildElementInfoAttribute(typeof(SheetViews))]
[ChildElementInfoAttribute(typeof(SheetFormatProperties))]
[ChildElementInfoAttribute(typeof(Columns))]
[ChildElementInfoAttribute(typeof(SheetData))]
[ChildElementInfoAttribute(typeof(SheetCalculationProperties))]
[ChildElementInfoAttribute(typeof(SheetProtection))]
[ChildElementInfoAttribute(typeof(ProtectedRanges))]
[ChildElementInfoAttribute(typeof(Scenarios))]
[ChildElementInfoAttribute(typeof(AutoFilter))]
[ChildElementInfoAttribute(typeof(SortState))]
[ChildElementInfoAttribute(typeof(DataConsolidate))]
[ChildElementInfoAttribute(typeof(CustomSheetViews))]
[ChildElementInfoAttribute(typeof(MergeCells))]
[ChildElementInfoAttribute(typeof(PhoneticProperties))]
[ChildElementInfoAttribute(typeof(ConditionalFormatting))]
[ChildElementInfoAttribute(typeof(DataValidations))]
[ChildElementInfoAttribute(typeof(SheetProperties))]
[ChildElementInfoAttribute(typeof(PrintOptions))]
[ChildElementInfoAttribute(typeof(PageMargins))]
[ChildElementInfoAttribute(typeof(PageSetup))]
[ChildElementInfoAttribute(typeof(HeaderFooter))]
[ChildElementInfoAttribute(typeof(RowBreaks))]
[ChildElementInfoAttribute(typeof(ColumnBreaks))]
[ChildElementInfoAttribute(typeof(CustomProperties))]
[ChildElementInfoAttribute(typeof(CellWatches))]
[ChildElementInfoAttribute(typeof(IgnoredErrors))]
[ChildElementInfoAttribute(typeof(SmartTags))]
[ChildElementInfoAttribute(typeof(Drawing))]
[ChildElementInfoAttribute(typeof(LegacyDrawing))]
[ChildElementInfoAttribute(typeof(LegacyDrawingHeaderFooter))]
[ChildElementInfoAttribute(typeof(DrawingHeaderFooter), FileFormatVersions.Office2010)]
[ChildElementInfoAttribute(typeof(Picture))]
[ChildElementInfoAttribute(typeof(OleObjects))]
[ChildElementInfoAttribute(typeof(Controls))]
[ChildElementInfoAttribute(typeof(WebPublishItems))]
public class Worksheet : OpenXmlPartRootElement

using System;
using System.Linq;
using DocumentFormat.OpenXml.Packaging;
using DocumentFormat.OpenXml.Spreadsheet;

namespace WorkSheetEx
{
    class Program
    {
        static void Main(string[] args)
        {
            string fileName = @"C:\Users\Public\Documents\WorksheetEx.xlsx";
            
            using (SpreadsheetDocument spreadSheet = SpreadsheetDocument.Open(fileName, true))
            {
                // Add a WorksheetPart.
                WorksheetPart newWorksheetPart = spreadSheet.WorkbookPart.AddNewPart<WorksheetPart>();
                newWorksheetPart.Worksheet = new Worksheet(new SheetData());

                // Create Sheets object.
                Sheets sheets = spreadSheet.WorkbookPart.Workbook.GetFirstChild<Sheets>();
                string relationshipId = spreadSheet.WorkbookPart.GetIdOfPart(newWorksheetPart);

                // Create a unique ID for the new worksheet.
                uint sheetId = 1;
                if (sheets.Elements<Sheet>().Count() > 0)
                {
                    sheetId = sheets.Elements<Sheet>().Select(s => s.SheetId.Value).Max() + 1;
                }

                // Give the new worksheet a name.
                string sheetName = "mySheet" + sheetId;

                // Append the new worksheet and associate it with the workbook.
                Sheet sheet = new Sheet() { Id = relationshipId, SheetId = sheetId, Name = sheetName };
                sheets.Append(sheet);
            }
            Console.WriteLine("All done.");
            Console.ReadKey();
        }
    }
}