var file = 'Path_to_pre_existing_Excel_File/excel_file.xlsx';
var bytes = File(file).readAsBytesSync();
var excel = Excel.decodeBytes(bytes);
for (var table in excel.tables.keys) {
  print(table); //sheet Name
  print(excel.tables[table].maxColumns);
  print(excel.tables[table].maxRows);
  for (var row in excel.tables[table].rows) {
    for (var cell in row) {
      print('cell ${cell.rowIndex}/${cell.columnIndex}');
      final value = cell.value;
      final numFormat = cell.cellStyle?.numberFormat ?? NumFormat.standard_0;
      switch(value){
        case null:
          print('  empty cell');
          print('  format: ${numFormat}');
        case TextCellValue():
          print('  text: ${value.value}');
        case FormulaCellValue():
          print('  formula: ${value.formula}');
          print('  format: ${numFormat}');
        case IntCellValue():
          print('  int: ${value.value}');
          print('  format: ${numFormat}');
        case BoolCellValue():
          print('  bool: ${value.value ? 'YES!!' : 'NO..' }');
          print('  format: ${numFormat}');
        case DoubleCellValue():
          print('  double: ${value.value}');
          print('  format: ${numFormat}');
        case DateCellValue():
          print('  date: ${value.year} ${value.month} ${value.day} (${value.asDateTimeLocal()})');
        case TimeCellValue():
          print('  time: ${value.hour} ${value.minute} ... (${value.asDuration()})');
        case DateTimeCellValue():
          print('  date with time: ${value.year} ${value.month} ${value.day} ${value.hour} ... (${value.asDateTimeLocal()})');
      }

      print('$row');
    }
  }
}

/// Use FilePicker to pick files in Flutter Web

FilePickerResult pickedFile = await FilePicker.platform.pickFiles(
  type: FileType.custom,
  allowedExtensions: ['xlsx'],
  allowMultiple: false,
);

/// file might be picked

if (pickedFile != null) {
  var bytes = pickedFile.files.single.bytes;
  var excel = Excel.decodeBytes(bytes);
  for (var table in excel.tables.keys) {
    print(table); //sheet Name
    print(excel.tables[table].maxColumns);
    print(excel.tables[table].maxRows);
    for (var row in excel.tables[table].rows) {
      print('$row');
    }
  }
}

import 'package:flutter/services.dart' show ByteData, rootBundle;

/* Your ......other important..... code here */

ByteData data = await rootBundle.load('assets/existing_excel_file.xlsx');
var bytes = data.buffer.asUint8List(data.offsetInBytes, data.lengthInBytes);
var excel = Excel.decodeBytes(bytes);

for (var table in excel.tables.keys) {
  print(table); //sheet Name
  print(excel.tables[table].maxColumns);
  print(excel.tables[table].maxRows);
  for (var row in excel.tables[table].rows) {
    print('$row');
  }
}

// automatically creates 1 empty sheet: Sheet1
var excel = Excel.createExcel();

/*
 * sheetObject.updateCell(cell, value, { CellStyle (Optional)});
 * sheetObject created by calling - // Sheet sheetObject = excel['SheetName'];
 * cell can be identified with Cell Address or by 2D array having row and column Index;
 * Cell Style options are optional
 */

Sheet sheetObject = excel['SheetName'];

CellStyle cellStyle = CellStyle(backgroundColorHex: '#1AFF1A', fontFamily :getFontFamily(FontFamily.Calibri));

cellStyle.underline = Underline.Single; // or Underline.Double


var cell = sheetObject.cell(CellIndex.indexByString('A1'));
cell.value = null; // removing any value
cell.value = TextCellValue('Some Text');
cell.value = IntCellValue(8);
cell.value = BoolCellValue(true);
cell.value = DoubleCellValue(13.37);
cell.value = DateCellValue(year: 2023, month: 4, day: 20);
cell.value = TimeCellValue(hour: 20, minute: 15, second: 5, millisecond: ...);
cell.value = DateTimeCellValue(year: 2023, month: 4, day: 20, hour: 15, ...);
cell.cellStyle = cellStyle;

// setting the number style
cell.cellStyle = (cell.cellStyle ?? CellStyle()).copyWith(

  /// for IntCellValue, DoubleCellValue and BoolCellValue use; 
  numberFormat: CustomNumericNumFormat('#,##0.00 \\m\\²'),

  /// for DateCellValue and DateTimeCellValue use:
  numberFormat: CustomDateTimeNumFormat('m/d/yy h:mm'),

  /// for TimeCellValue use:
  numberFormat: CustomDateTimeNumFormat('mm:ss'),

  /// a builtin format for dates
  numberFormat: NumFormat.standard_14,
  
  /// a builtin format that uses a red text color for negative numbers
  numberFormat: NumFormat.standard_38,

  // The numberFormat changes automatially if you set a CellValue that 
  // does not work with the numberFormat set previously. So in case you
  // want to set a new value, e.g. from a date to a decimal number, 
  // make sure you set the new value first and then your custom
  // numberFormat).
);


// printing cell-type
print('CellType: ' + switch(cell.value) {
  null => 'empty cell',
  TextCellValue() => 'text',
  FormulaCellValue() => 'formula',
  IntCellValue() => 'int',
  BoolCellValue() => 'bool',
  DoubleCellValue() => 'double',
  DateCellValue() => 'date',
  TimeCellValue => 'time',
  DateTimeCellValue => 'date with time',
});

///
/// Inserting and removing column and rows

// insert column at index = 8
sheetObject.insertColumn(8);

// remove column at index = 18
sheetObject.removeColumn(18);

// insert row at index = 82
sheetObject.insertRow(82);

// remove row at index = 80
sheetObject.removeRow(80);

/*
 *
 * Defines thin borders on the left and right of the cell, red thin border on the top
 * and blue medium border on the bottom.
 *
 */

CellStyle cellStyle = CellStyle(
  leftBorder: Border(borderStyle: BorderStyle.Thin),
  rightBorder: Border(borderStyle: BorderStyle.Thin),
  topBorder: Border(borderStyle: BorderStyle.Thin, borderColorHex: 'FFFF0000'),
  bottomBorder: Border(borderStyle: BorderStyle.Medium, borderColorHex: 'FF0000FF'),
);

/*
 * set rtl to true for making sheet to right-to-left
 * default value of rtl = false ( which means the fresh or default sheet is ltr )
 *
 */

var sheetObject = excel['SheetName'];
sheetObject.rtl = true;

/*
 * excel.copy(String 'existingSheetName', String 'anotherSheetName');
 * existingSheetName should exist in excel.tables.keys in order to successfully copy
 * if anotherSheetName does not exist then it will be automatically created.
 *
 */

excel.copy('existingSheetName', 'anotherSheetName');

/*
 * excel.rename(String 'existingSheetName', String 'newSheetName');
 * existingSheetName should exist in excel.tables.keys in order to successfully rename
 *
 */

excel.rename('existingSheetName', 'newSheetName');

/*
 * excel.delete(String 'existingSheetName');
 * (existingSheetName should exist in excel.tables.keys) and (excel.tables.keys.length >= 2), in order to successfully delete.
 *
 */

excel.delete('existingSheetName');

/*
 * excel.link(String 'sheetName', Sheet sheetObject);
 *
 * Any operations performed on (object of 'sheetName') or sheetObject then the operation is performed on both.
 * if 'sheetName' does not exist then it will be automatically created and linked with the sheetObject's operation.
 *
 */

excel.link('sheetName', sheetObject);

/*
 * excel.unLink(String 'sheetName');
 * In order to successfully unLink the 'sheetName' then it must exist in excel.tables.keys
 *
 */

excel.unLink('sheetName');

// After calling the above function be sure to re-make a new reference of this.

Sheet unlinked_sheetObject = excel['sheetName'];

/*
 * sheetObject.merge(CellIndex starting_cell, CellIndex ending_cell, TextCellValue('customValue'));
 * sheetObject created by calling - // Sheet sheetObject = excel['SheetName'];
 * starting_cell and ending_cell can be identified with Cell Address or by 2D array having row and column Index;
 * customValue is optional
 */

sheetObject.merge(CellIndex.indexByString('A1'), CellIndex.indexByString('E4'), customValue: TextCellValue('Put this text after merge'));

// Check which cells are merged

sheetObject.spannedItems.forEach((cells) {
  print('Merged:' + cells.toString());
});

/*
 * sheetObject.unMerge(cell);
 * sheetObject created by calling - // Sheet sheetObject = excel['SheetName'];
 * cell should be identified with string only with an example as 'A1:E4'.
 * to check if 'A1:E4' is un-merged or not
 * call the method excel.getMergedCells(sheet); and verify that it is not present in it.
 */

sheetObject.unMerge('A1:E4');

/*
 * int replacedCount = sheetObject.findAndReplace(source, target);
 * sheetObject created by calling - // Sheet sheetObject = excel['SheetName'];
 * source is the string or ( User's Custom Pattern Matching RegExp )
 * target is the string which is put in cells in place of source
 *
 * it returns the number of replacements made
 */

int replacedCount = sheetObject.findAndReplace('Flutter', 'Google');

/*
 * sheetObject.insertRowIterables(list-iterables, rowIndex, iterable-options?);
 * sheetObject created by calling - // Sheet sheetObject = excel['SheetName'];
 * list-iterables === list of iterables which has to be put in specific row
 * rowIndex === the row in which the iterables has to be put
 * Iterable options are optional
 */

/// It will put the list-iterables in the 8th index row
List<CellValue> dataList = [TextCellValue('Google'), TextCellValue('loves'), TextCellValue('Flutter'), TextCellValue('and'), TextCellValue('Flutter'), TextCellValue('loves'), TextCellValue('Excel')];

sheetObject.insertRowIterables(dataList, 8);

/*
 * sheetObject.appendRow(list-iterables);
 * sheetObject created by calling - // Sheet sheetObject = excel['SheetName'];
 * list-iterables === list of iterables
 */

sheetObject.appendRow([TextCellValue('Flutter'), TextCellValue('till'), TextCellValue('Eternity')]);

/*
 * method which returns the name of the default sheet
 * excel.getDefaultSheet();
 */

var defaultSheet = excel.getDefaultSheet();
print('Default Sheet:' + defaultSheet.toString());

/*
 * method which sets the name of the default sheet
 * returns bool if successful then true else false
 * excel.setDefaultSheet(sheet);
 * sheet = 'SheetName'
 */

var isSet = excel.setDefaultSheet(sheet);
if (isSet) {
  print('$sheet is set to default sheet.');
} else {
  print('Unable to set $sheet to default sheet.');
}

// when you are in flutter web then save() downloads the excel file.

// Call function save() to download the file
var fileBytes = excel.save(fileName: 'My_Excel_File_Name.xlsx');

var fileBytes = excel.save();
var directory = await getApplicationDocumentsDirectory();

File(join('$directory/output_file_name.xlsx'))
  ..createSync(recursive: true)
  ..writeAsBytesSync(fileBytes);