Unhandled Exception: MissingPluginException(No implementation found for method scanBarcode on channel flutter_barcode_scanner)

im trying to create an barcode scanner by: https://pub.dev/packages/flutter_barcode_scanner/install.

when i run my codes i get this error :

E/flutter ( 9248): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: MissingPluginException(No implementation found for method scanBarcode on channel flutter_barcode_scanner)
E/flutter ( 9248): #0      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:165:7)
E/flutter ( 9248): <asynchronous suspension>
E/flutter ( 9248): #1      FlutterBarcodeScanner.scanBarcode (package:flutter_barcode_scanner/flutter_barcode_scanner.dart:43:9)
E/flutter ( 9248): <asynchronous suspension>
E/flutter ( 9248): #2      _MyAppState.scanBarcodeNormal (package:styleupapp1/main.dart:46:24)
E/flutter ( 9248): <asynchronous suspension>
E/flutter ( 9248): 

here's my codes:

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter_barcode_scanner/flutter_barcode_scanner.dart';

void main() => runApp(MyApp());

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  String _scanBarcode = 'Unknown';

  @override
  void initState() {
    super.initState();
  }

  Future<void> startBarcodeScanStream() async {
    FlutterBarcodeScanner.getBarcodeStreamReceiver(
        '#ff6666', 'Cancel', true, ScanMode.BARCODE)!
        .listen((barcode) => print(barcode));
  }

  Future<void> scanQR() async {
    String barcodeScanRes;
    try {
      barcodeScanRes = await FlutterBarcodeScanner.scanBarcode(
          '#ff6666', 'Cancel', true, ScanMode.QR);
      print(barcodeScanRes);
    } on PlatformException {
      barcodeScanRes = 'Failed to get platform version.';
    }
//barcode scanner flutter ant
    setState(() {
      _scanBarcode = barcodeScanRes;
    });
  }

  Future<void> scanBarcodeNormal() async {
    String barcodeScanRes;
    try {
      barcodeScanRes = await FlutterBarcodeScanner.scanBarcode(
          '#ff6666', 'Cancel', true, ScanMode.BARCODE);
      print(barcodeScanRes);
    } on PlatformException {
      barcodeScanRes = 'Failed to get platform version.';
    }

    if (!mounted) return;
    setState(() {
      _scanBarcode = barcodeScanRes;
    });
  }
//barcode scanner flutter ant
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        debugShowCheckedModeBanner: false,
        home: Scaffold(
            appBar: AppBar(title: const Text('Barcode Scanner')),
            body: Builder(builder: (BuildContext context) {
              return Container(
                  alignment: Alignment.center,
                  child: Flex(
                      direction: Axis.vertical,
                      mainAxisAlignment: MainAxisAlignment.center,
                      children: <Widget>[
                        ElevatedButton(
                            onPressed: () => scanBarcodeNormal(),
                            child: const Text('Barcode scan')),
                        ElevatedButton(
                            onPressed: () => scanQR(),
                            child: const Text('QR scan')),
                        ElevatedButton(
                            onPressed: () => startBarcodeScanStream(),
                            child: const Text('Barcode scan stream')),
                        Text('Scan result : $_scanBarcode\n',
                            style: const TextStyle(fontSize: 20))
                      ]));
            })));
  }
}

has anyone experienced this error? i don't know what to do i tried different ways and packages but everyone gave me same error . it's so important to me thanks for ur answers.

i asked once but no one answered. i really need to fix it.