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");

// ストリームからも読める
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

// 巨大ファイルはシート単位の遅延ロードで開く
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");

// Excel のキャッシュ値をそのまま読むため、ロード時に再評価はしない。
// 自前で計算し直したい場合だけ明示的に呼ぶ。
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