ClosedXML 1594 demo

Test1594.cs

public void Main()
{
	var workbook = new XLWorkbook();
	var worksheet = workbook.Worksheets.Add("Dati");

	DataGenerationWithBigData(worksheet);

	worksheet.Columns().AdjustToContents();

	worksheet.PageSetup.PageOrientation = XLPageOrientation.Portrait;
	worksheet.PageSetup.PaperSize = XLPaperSize.A4Paper;

	workbook.CalculateMode = XLCalculateMode.Auto;

	workbook.SaveAs(@"C:\temp\file.xlsx");
}

public static void DataGenerationWithBigData(IXLWorksheet worksheet)
{
	for (var i = 0; i < 15000; i++)
	{
		for (var col = 0; col < 25; col++)
		{
			worksheet.Cell(i + 1, col + 1).Value = "X";
		}
	}
}

public static string ColumnIndexToColumnLetter(int colIndex)
{
	int div = colIndex;
	string colLetter = String.Empty;
	int mod = 0;

	while (div > 0)
	{
		mod = (div - 1) % 26;
		colLetter = (char)(65 + mod) + colLetter;
		div = ((div - mod) / 26);
	}
	return colLetter;
}