How to export a Barcode generator as a pdf (SfBarcodeGenerator) ?

dependencies:
  syncfusion_flutter_barcodes: ^19.3.54
  syncfusion_flutter_pdf: ^19.3.54-beta

/// Dart import
import 'dart:async';
import 'dart:io';
import 'dart:ui' as dart_ui;
 
/// Barcode import
import 'package:syncfusion_flutter_barcodes/barcodes.dart';
 
/// Pdf import
import 'package:syncfusion_flutter_pdf/pdf.dart';

// Global key for Barcode class
final GlobalKey<_BarcodeState > barcodeKey = GlobalKey();
 
// Barcode class to render barcode using SfBarcodeGenerator
class Barcode extends StatefulWidget {
  const Barcode({Key? key}) : super(key: key);
 
  @override
  _BarcodeState createState() => _BarcodeState();
}
 
class _ BarcodeState extends State<Barcode> {
  @override
  Widget build(BuildContext context) {
    return RepaintBoundary(
         /// Rendered a barcode using the SfBarcodeGenerator widget
        child: SfBarcodeGenerator(
            value: 'CODE128',
            showValue: true,
            symbology: Code128(module: 2)
        )
    );
  }
}

Future<dart_ui.Image> convertToImage({double pixelRatio = 1.0}) async {
    // Get the render object from context and store in the RenderRepaintBoundary object.
    final RenderRepaintBoundary boundary = context.findRenderObject()
        as RenderRepaintBoundary; 
 
    // Convert the repaint boundary as image
    final dart_ui.Image image =
        await boundary.toImage(pixelRatio: pixelRatio); 
 
    return image;
  }

///Class to render the barcode along with a button to export as PDF document.
class ExportBarcode extends StatefulWidget {
  const ExportBarcode({Key? key}) : super(key: key);
 
  @override
  _ExportBarcodeState createState() => _ExportBarcodeState();
}
 
class _ExportBarcodeState extends State<ExportBarcode> {
  _ExportBarcodeState();
 
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: const Text('Flutter Barcode Export'),
        ),
        body: Center(
          child: Padding(
            padding: const EdgeInsets.all(8.0),
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  SizedBox(
                    height: 300,
                    width: 300,
                    child: Barcode(
                      key: barcodeKey,
                    ),
                  ),
                  const SizedBox(
                    height: 100,
                  ),
                  Container(
                      width: 110,
                      color: Colors.green,
                      child: IconButton(
                        onPressed: () {
                          /// Snackbar messenger to indicate that the rendered barcode is being exported as PDF
                          ScaffoldMessenger.of(context)
                              .showSnackBar(const SnackBar(
                            behavior: SnackBarBehavior.floating,
                            duration: Duration(milliseconds: 2000),
                            shape: RoundedRectangleBorder(
                                borderRadius:
                                    BorderRadius.all(Radius.circular(5))),
                            content:
                                Text('Barcode is being exported as PDF document'),
                          ));
                          _renderPdf();
                        },
                        icon: Row(
                          children: const <Widget>[
                            Icon(Icons.picture_as_pdf, color: Colors.black),
                            Text('Export to pdf'),
                          ],
                        ),
                      )),
                ]),
          ),
        ));
  }
}

Future<void> _renderPdf() async {
    // Create a new PDF document.
    final PdfDocument document = PdfDocument();
    // Create a pdf bitmap for the rendered barcode image.
    final PdfBitmap bitmap = PdfBitmap(await _readImageData());
    // set the necessary page settings for the pdf document such as margin, size etc..
    document.pageSettings.margins.all = 0;
    document.pageSettings.size =
        Size(bitmap.width.toDouble(), bitmap.height.toDouble());
    // Create a PdfPage page object and assign the pdf document's pages to it.
    final PdfPage page = document.pages.add();
    // Retrieve the pdf page client size
    final Size pageSize = page.getClientSize();
    // Draw an image into graphics using the bitmap.
    page.graphics.drawImage(
        bitmap, Rect.fromLTWH(0, 0, pageSize.width, pageSize.height));
 
    // Snackbar indication for barcode export operation
    ScaffoldMessenger.of(context).hideCurrentSnackBar();
    ScaffoldMessenger.of(context).showSnackBar(const SnackBar(
      behavior: SnackBarBehavior.floating,
      shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.all(Radius.circular(5))),
      duration: Duration(milliseconds: 200),
      content: Text('Barcode has been exported as PDF document.'),
    ));
    //Save and dispose the document.
    final List<int> bytes = document.save();
    document.dispose();
}

/// Method to read the rendered barcode image and return the image data for processing.  Future<List<int>> _readImageData() async {
    // Called the convertToImage method to retrieve the rendered barcode image using its key.
    final dart_ui.Image data =
        await barcodeKey.currentState!.convertToImage(pixelRatio: 3.0);
    final ByteData? bytes =
        await data.toByteData(format: dart_ui.ImageByteFormat.png);
    return bytes!.buffer.asUint8List(bytes.offsetInBytes, bytes.lengthInBytes);
  }

path_provider: ^2.0.1
open_file: ^3.1.0 #Open source library to launch the PDF file in mobile devices

/// Path provider library import
import 'package:path_provider/path_provider.dart';
/// open file library import
import 'package:open_file/open_file.dart';

   //Get the external storage directory.
    Directory directory = (await getApplicationDocumentsDirectory());
    //Get the directory path.
    String path = directory.path;
    //Create an empty file to write the PDF data.
    File file = File('$path/output.pdf');
    //Write the PDF data.
    await file.writeAsBytes(bytes, flush: true);
    //Open the PDF document on mobile.
    OpenFile.open('$path/output.pdf');