How do I update a cell in an existing Excel file with Dart?

Decode the file with Excel.decodeBytes, call updateCell on the sheet with the new value, then save the workbook. Pass the cell's current cellStyle if you want to keep its existing formatting.

How to edit an existing Excel file

Open a workbook you already have, change what you need, and write it back with everything else untouched.

Install#

dart pub add excel_plus

import 'package:excel_plus/excel_plus.dart';

Open, change, save#

The usual template workflow. Read the file, update the cells that matter, save it under a new name.

import 'dart:io';
import 'package:excel_plus/excel_plus.dart';

void main() {
  final excel = Excel.decodeBytes(File('template.xlsx').readAsBytesSync());
  final sheet = excel['Sheet1'];

  sheet.updateCell(CellIndex.indexByString('B2'), TextCellValue('Updated'));
  sheet.updateCell(CellIndex.indexByString('B3'), IntCellValue(2026));

  File('output.xlsx').writeAsBytesSync(excel.save()!);
}

Parts of the workbook that are not modelled, such as embedded images or printer settings, are carried across to the saved file byte for byte, so opening and saving does not quietly strip them.

Keeping a cell's existing style#

Writing a value replaces the cell. To change only the text and keep the formatting the template already had, pass the old style back in.

final index = CellIndex.indexByString('B2');
final existing = sheet.cell(index).cellStyle;

sheet.updateCell(index, TextCellValue('Updated'), cellStyle: existing);

Rows and columns#

sheet.insertRow(2);
sheet.removeRow(5);

sheet.insertColumn(1);
sheet.removeColumn(3);

Merging#

sheet.merge(
  CellIndex.indexByString('A1'),
  CellIndex.indexByString('D1'),
  customValue: TextCellValue('Merged title'),
);

sheet.unMerge('A1:D1');

Find and replace#

sheet.findAndReplace('draft', 'final');

Column width and row height#

sheet.setColumnWidth(0, 24);
sheet.setRowHeight(0, 28);
sheet.setColumnAutoFit(1);