How to export Flutter Spark bar charts as a pdf (SfSparkBarChart)?

dependencies:
  syncfusion_flutter_charts: ^19.3.48
  syncfusion_flutter_pdf: ^19.3.48-beta

/// Dart import
import 'dart:async';
import 'dart:io';
import 'dart:ui' as dart_ui;
 
/// Chart import
import 'package:syncfusion_flutter_charts/sparkcharts.dart';
 
/// Pdf import
import 'package:syncfusion_flutter_pdf/pdf.dart';

// Global key for SparkBarChart class
final GlobalKey<_SparkBarChartState> chartKey = GlobalKey();
 
// SparkBarChart class to render the SfSparkBarChart
class SparkBarChart extends StatefulWidget {
  const SparkBarChart({Key? key}) : super(key: key);
 
  @override
  _SparkBarChartState createState() => _SparkBarChartState();
}
 
class _SparkBarChartState extends State<SparkBarChart> {
  @override
  Widget build(BuildContext context) {
    return RepaintBoundary(
      child: SfSparkBarChart(
        axisLineWidth: 0,
        data: const <double>[ 
             5, 6, 5, 7, 4, 3, 9, 5, 6, 5, 7, 8, 4, 5, 3, 4, 11, 10, 2, 12, 4, 7,  6, 8
        ],
        highPointColor: Colors.red,
        lowPointColor: Colors.red,
        firstPointColor: Colors.orange,
        lastPointColor: Colors.orange,
      ),
    );
  }

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 Spark bar chart along with a button to export as PDF document.
class ExportSparkChart extends StatefulWidget {
  const ExportSparkChart({Key? key}) : super(key: key);
 
  @override
  _ExportSparkChartState createState() => _ExportSparkChartState();
}
 
class _ExportSparkChartState extends State<ExportSparkChart> {
  _ExportSparkChartState();
 
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: const Text('Flutter Spark Chart Export'),
        ),
        body: Padding(
          padding: const EdgeInsets.all(8.0),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.center,
            children: <Widget>[
            Expanded(
                // Renders the SfSparkBarChart
                child: SparkBarChart(
                    // set the key for the SparkBarChart class
                    key: chartKey,
                )
            ),
            const SizedBox(
              height: 50,
            ),
            Container(
                width: 110,
                color: Colors.green,
                child: IconButton(
                  onPressed: () {
                    // Snackbar messenger to indicate that the spark chart 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('Spark Chart is being exported as PDF document'),
                    ));
                    /// Method which perform the pdf export operation
                    _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 spark chart 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 chart 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('Spark Chart has been exported as PDF document.'),
    ));
    //Save and dispose the document.
    final List<int> bytes = document.save();
    document.dispose();
}

/// Method to read the rendered spark bar chart image and return the image data for processing.
  Future<List<int>> _readImageData() async {
    // Called the convertToImage method to retrieve the rendered spark bar chart image using its key.
    final dart_ui.Image data =
        await chartKey.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');