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.

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