C# EXCEL LIBRARYHigh-performance .NET Core Excel Framework

//New instance of ExcelEngine is created 
//Equivalent to launching Microsoft Excel with no workbooks open
//Instantiate the spreadsheet creation engine
ExcelEngine excelEngine = new ExcelEngine();

//Instantiate the Excel application object
IApplication application = excelEngine.Excel;

//Assigns default application version
application.DefaultVersion = ExcelVersion.Excel2013;

//A existing workbook is opened.              
string basePath = _hostingEnvironment.WebRootPath + @"\XlsIO\Sample.xlsx";              
FileStream sampleFile = new FileStream(basePath, FileMode.Open);

IWorkbook workbook = application.Workbooks.Open(sampleFile);

//Access first worksheet from the workbook.
IWorksheet worksheet = workbook.Worksheets[0];

//Set Text in cell A3.
worksheet.Range["A3"].Text ="Hello World";

//Defining the ContentType for excel file.
string ContentType = "Application/msexcel";

//Define the file name.
string fileName = "Output.xlsx";

//Creating stream object.
MemoryStream stream = new MemoryStream();

//Saving the workbook to stream in XLSX format
workbook.SaveAs(stream);

stream.Position = 0;

//Closing the workbook.

workbook.Close();

//Dispose the Excel engine
excelEngine.Dispose();

//Creates a FileContentResult object by using the file contents, content type, and file name.
return File(stream, ContentType, fileName);