Reading and writing XLSX (OOXML) is handled by unvell.ReoGrid.IO.Excel. It depends on no external packages (neither the Open XML SDK nor EPPlus is used).

Everything is bundled with the One packages.

Reading and writing

using unvell.ReoGrid.Core;
using unvell.ReoGrid.IO.Excel;

Workbook loaded = XlsxReader.Read("book.xlsx");
XlsxWriter.Write(wb, "out.xlsx");

// a stream works too
using var stream = File.OpenRead("book.xlsx");
Workbook fromStream = XlsxReader.Read(stream);

XlsxWriter.Write has a stream overload as well.

Streaming reads

Reading is streamed through XmlReader directly into the sparse store. Memory usage is proportional to the number of cells that actually exist (not the sheet’s declared dimensions).

Lazy loading for huge files

// open a huge file with per-sheet lazy loading
using var virtualBook = XlsxReader.OpenVirtual("large.xlsx", SheetLoadMode.OnDemand);

VirtualWorkbook is IDisposable. It holds on to the underlying stream, so dispose it when you are done.

Column widths

Excel stores a column width as a number of digits of the Normal font, and measures that digit on the screen showing the sheet. The width depends on the font and the DPI, and does not scale with the DPI: Arial 10’s digit is 7 px at 100 %, but 11 px at 150 % (7.33 logical px), not 10.5. Yu Gothic 11’s is 8 px at every scale.

Set the measurement once in a UI host and opened xlsx columns come out as wide as Excel draws them on the same screen. Saving converts back with the same measurement, so a width nobody touched is written back as the number that was read.

// open column widths as wide as Excel draws them on this screen (set once in a UI host)
XlsxColumnWidths.MaxDigitWidthMeasurer =
	(family, sizePt) => GdiTextMetrics.MaxDigitWidth(family, sizePt, grid.DeviceDpi);

WPF and Avalonia do not draw with GDI, so pass XlsxColumnWidths.ExcelMaxDigitWidth, which looks Excel’s digit width up in a built-in table at the screen’s DPI. The table holds GDI measurements — the way Excel measures — for each pixel size of the font, so columns match Excel at 150 % and 200 % too. On Avalonia, use 96 × TopLevel.RenderScaling as the DPI.

// WPF / Avalonia: Excel's digit widths from the built-in table, at this screen's DPI
double dpi = VisualTreeHelper.GetDpi(grid).PixelsPerInchX;
XlsxColumnWidths.MaxDigitWidthMeasurer =
	(family, sizePt) => XlsxColumnWidths.ExcelMaxDigitWidth(family, sizePt, dpi);

Left unset (on a server, for instance), the digit width Excel measures at 100 % comes from the same table: 7 px for Calibri 11, Aptos Narrow 11 and Arial 10, 8 px for Yu Gothic 11 and MS PGothic 11. Japanese workbooks open as wide as in Excel at 100 % too. A font not in the table counts as Calibri, Excel’s default.

How formulas are handled

Formulas are not re-evaluated on load. The cached values saved by Excel are used as-is.

var wb = XlsxReader.Read("book.xlsx");

// The cached values Excel saved are read as-is, so nothing is re-evaluated on load.
// Call this only when you want to compute them yourself.
foreach (var sheet in wb.Worksheets)
	sheet.Recalculate();

There is a reason for this design: even for files containing functions that V5 does not implement, the values Excel calculated are displayed as-is. Re-evaluating them would turn them into #NAME?.

What is supported

Not supported

What to read next

• PDF Export
• XLSX Compatibility Matrix