如何将Open XML文档保存(和打开)为Excel文件？

using DocumentFormat.OpenXml;
using DocumentFormat.OpenXml.Packaging;
using DocumentFormat.OpenXml.Spreadsheet;

using (SpreadsheetDocument spreadsheetDocument = SpreadsheetDocument.Create("output.xlsx", SpreadsheetDocumentType.Workbook))
{
    // 创建Workbook部分
    spreadsheetDocument.AddWorkbookPart();
    spreadsheetDocument.WorkbookPart.Workbook = new Workbook();

    // 创建Worksheet部分
    spreadsheetDocument.WorkbookPart.AddNewPart<WorksheetPart>();
    spreadsheetDocument.WorkbookPart.WorksheetParts.First().Worksheet = new Worksheet(new SheetData());

    // 创建Sheet部分
    spreadsheetDocument.WorkbookPart.Workbook.AppendChild(new Sheets());
    spreadsheetDocument.WorkbookPart.Workbook.GetFirstChild<Sheets>().AppendChild(new Sheet()
    {
        Id = spreadsheetDocument.WorkbookPart.GetIdOfPart(spreadsheetDocument.WorkbookPart.WorksheetParts.First()),
        SheetId = 1,
        Name = "Sheet1"
    });

    // 保存并关闭文档
    spreadsheetDocument.WorkbookPart.Workbook.Save();
    spreadsheetDocument.Close();
}

using (SpreadsheetDocument spreadsheetDocument = SpreadsheetDocument.Open("input.xlsx", true))
{
    // 获取第一个Worksheet部分
    WorksheetPart worksheetPart = spreadsheetDocument.WorkbookPart.WorksheetParts.First();
    Worksheet worksheet = worksheetPart.Worksheet;

    // 在指定单元格写入数据
    Cell cell = InsertCellInWorksheet("A", 1, worksheetPart);
    cell.CellValue = new CellValue("Hello World!");
    cell.DataType = new EnumValue<CellValues>(CellValues.String);

    // 保存并关闭文档
    worksheet.Save();
    spreadsheetDocument.Close();
}