title: In Flutter 3.0, the Qr Code Scanner is giving an error
body: <p>I am updating an old project. This qr code scanner is giving an error.The project had previously run on flutter 2.10. There are errors in Flutter 3.0.</p>
  <pre><code>import 'package:flutter/material.dart';
  import 'package:qr_code_scanner/qr_code_scanner.dart';
  import 'dart:io';
  import 'package:flutter/foundation.dart';
  
  void main() {
    runApp(const MyApp());
  }
  
  class MyApp extends StatelessWidget {
    const MyApp({Key? key}) : super(key: key);
  
    // This widget is the root of your application.
    @override
    Widget build(BuildContext context) {
      return MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          
          primarySwatch: Colors.blue,
        ),
        home: const MyHomePage(title: 'Flutter Demo Home Page'),
      );
    }
  }
  
  class MyHomePage extends StatefulWidget {
    const MyHomePage({Key? key, required this.title}) : super(key: key);
  
  
    final String title;
  
    @override
    State&lt;MyHomePage&gt; createState() =&gt; _MyHomePageState();
  }
  
  class _MyHomePageState extends State&lt;MyHomePage&gt; {
    final GlobalKey qrKey = GlobalKey(debugLabel: 'QR');
    Barcode? result;
    QRViewController? controller;
  
    // In order to get hot reload to work we need to pause the camera if the platform
    // is android, or resume the camera if the platform is iOS.
    @override
    void reassemble() {
      super.reassemble();
      if (Platform.isAndroid) {
        controller!.pauseCamera();
      } else if (Platform.isIOS) {
        controller!.resumeCamera();
      }
    }
  
    @override
    Widget build(BuildContext context) {
      return Scaffold(
        body: Column(
          children: &lt;Widget&gt;[
            Expanded(
              flex: 5,
              child: QRView(
                key: qrKey,
                onQRViewCreated: _onQRViewCreated,
              ),
            ),
            Expanded(
              flex: 1,
              child: Center(
                child: (result != null)
                    ? Text(
                    'Barcode Type: ${describeEnum(result!.format)}   Data: ${result!.code}')
                    : Text('Scan a code'),
              ),
            )
          ],
        ),
      );
    }
  
    void _onQRViewCreated(QRViewController controller) {
      this.controller = controller;
      controller.scannedDataStream.listen((scanData) {
        setState(() {
          result = scanData;
        });
      });
    }
  
    @override
    void dispose() {
      controller?.dispose();
      super.dispose();
    }
  }
  </code></pre>
  <p>Error</p>
  <pre><code>Warning: unexpected element (uri:&quot;&quot;, local:&quot;base-extension&quot;). Expected elements are &lt;{}codename&gt;,&lt;{}layoutlib&gt;,&lt;{}api-level&gt;
  /C:/src/flutter/.pub-cache/hosted/pub.dartlang.org/qr_code_scanner-0.7.0/lib/src/qr_code_scanner.dart:68:20: Warning: Operand of null-aware operation '!' has type 'WidgetsBinding' which excludes null.
   - 'WidgetsBinding' is from 'package:flutter/src/widgets/binding.dart' ('/C:/src/flutter/packages/flutter/lib/src/widgets/binding.dart').
      WidgetsBinding.instance!.addObserver(_observer);
                     ^
  /C:/src/flutter/.pub-cache/hosted/pub.dartlang.org/qr_code_scanner-0.7.0/lib/src/qr_code_scanner.dart:86:20: Warning: Operand of null-aware operation '!' has type 'WidgetsBinding' which excludes null.
   - 'WidgetsBinding' is from 'package:flutter/src/widgets/binding.dart' ('/C:/src/flutter/packages/flutter/lib/src/widgets/binding.dart').
      WidgetsBinding.instance!.removeObserver(_observer);
                     ^
  e: C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\qr_code_scanner-0.7.0\android\src\main\kotlin\net\touchcapture\qr\flutterqr\QRView.kt: (23, 1): Class 'QRView' is not abstract and does not implement abstract member public abstract fun onRequestPermissionsResult(p0: Int, p1: Array&lt;(out) String!&gt;, p2: IntArray): Boolean defined in io.flutter.plugin.common.PluginRegistry.RequestPermissionsResultListener
  e: C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\qr_code_scanner-0.7.0\android\src\main\kotlin\net\touchcapture\qr\flutterqr\QRView.kt: (216, 26): Null can not be a value of a non-null type String
  e: C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\qr_code_scanner-0.7.0\android\src\main\kotlin\net\touchcapture\qr\flutterqr\QRView.kt: (247, 26): Null can not be a value of a non-null type String
  e: C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\qr_code_scanner-0.7.0\android\src\main\kotlin\net\touchcapture\qr\flutterqr\QRView.kt: (310, 5): 'onRequestPermissionsResult' overrides nothing
  e: C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\qr_code_scanner-0.7.0\android\src\main\kotlin\net\touchcapture\qr\flutterqr\QRViewFactory.kt: (10, 1): Class 'QRViewFactory' is not abstract and does not implement abstract base class member public abstract fun create(p0: Context?, p1: Int, p2: Any?): PlatformView defined in io.flutter.plugin.platform.PlatformViewFactory
  e: C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\qr_code_scanner-0.7.0\android\src\main\kotlin\net\touchcapture\qr\flutterqr\QRViewFactory.kt: (13, 5): 'create' overrides nothing
  
  FAILURE: Build failed with an exception.
  
  * What went wrong:
  Execution failed for task ':qr_code_scanner:compileDebugKotlin'.
  &gt; Compilation error. See log for more details
  
  * Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
  
  * Get more help at https://help.gradle.org
  
  BUILD FAILED in 21s
  Running Gradle task 'assembleDebug'...                             22.5s
  Exception: Gradle task assembleDebug failed with exit code 1
  </code></pre>
  <p>flutter doctor -v</p>
  <pre><code>[√] Flutter (Channel stable, 3.0.0, on Microsoft Windows [Version 10.0.19043.1645], locale en-US)
      • Flutter version 3.0.0 at C:\src\flutter
      • Upstream repository https://github.com/flutter/flutter.git
      • Framework revision ee4e09cce0 (2 days ago), 2022-05-09 16:45:18 -0700
      • Engine revision d1b9a6938a
      • Dart version 2.17.0
      • DevTools version 2.12.2
  
  Checking Android licenses is taking an unexpectedly long time...[√] Android toolchain - develop for Android devices (Android SDK version 32.1.0-rc1)
      • Android SDK at C:\Users\User\AppData\Local\Android\sdk
      • Platform android-32, build-tools 32.1.0-rc1
      • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
      • Java version OpenJDK Runtime Environment (build 11.0.11+9-b60-7590822)
      • All Android licenses accepted.
  
  [√] Chrome - develop for the web
      • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe
  
  [√] Visual Studio - develop for Windows (Visual Studio Professional 2022 17.1.3)
      • Visual Studio at C:\Program Files\Microsoft Visual Studio\2022\Professional
      • Visual Studio Professional 2022 version 17.1.32328.378
      • Windows 10 SDK version 10.0.19041.0
  
  [√] Android Studio (version 2021.1)
      • Android Studio at C:\Program Files\Android\Android Studio
      • Flutter plugin can be installed from:
         https://plugins.jetbrains.com/plugin/9212-flutter
      • Dart plugin can be installed from:
         https://plugins.jetbrains.com/plugin/6351-dart
      • Java version OpenJDK Runtime Environment (build 11.0.11+9-b60-7590822)
  
  [√] VS Code (version 1.67.1)
      • VS Code at C:\Users\User\AppData\Local\Programs\Microsoft VS Code
      • Flutter extension version 3.40.0
  
  [√] Connected device (5 available)
      • SM T500 (mobile)        • R9AR702P83X   • android-arm64  • Android 11 (API 30)
      • sdk gphone x86 (mobile) • emulator-5554 • android-x86    • Android 11 (API 30) (emulator)
      • Windows (desktop)       • windows       • windows-x64    • Microsoft Windows [Version 10.0.19043.1645]
      • Chrome (web)            • chrome        • web-javascript • Google Chrome 101.0.4951.54
      • Edge (web)              • edge          • web-javascript • Microsoft Edge 101.0.1210.39
  
  [√] HTTP Host Availability
      • All required HTTP hosts are available
  
  • No issues found!
  </code></pre>
  <p>What should I do to make it work? Before everything was fine, I updated my project to the latest version of flutter and now I get this error.</p>