flutter zxing2 scanner example

Question

Is there any working example for flutter Zxing2 pub package. I did tried the official pub package example [https://pub.dev/packages/zxing2/example | Dart Package] but it doesn’t work. I get the below error

I/CameraManagerGlobal( 5452): Connecting to camera service
E/flutter ( 5452): [ERROR:flutter/lib/ui/ui_dart_state.cc(213)] Unhandled Exception: CameraException(Uninitialized CameraController, startImageStream() was called on an uninitialized CameraController.)
E/flutter ( 5452): #0      CameraController._throwIfNotInitialized (package:camera/src/camera_controller.dart:769:7)
E/flutter ( 5452): #1      CameraController.startImageStream (package:camera/src/camera_controller.dart:370:5)
E/flutter ( 5452): #2      _MyHomePageState._onCameraSelected (package:test_camera/main.dart:83:26)
E/flutter ( 5452): #3      _MyHomePageState.initState (package:test_camera/main.dart:46:5)
E/flutter ( 5452): #4      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4796:57)
E/flutter ( 5452): #5      ComponentElement.mount (package:flutter/src/widgets/framework.dart:4631:5)
E/flutter ( 5452): #6      Element.inflateWidget (package:flutter/src/widgets/framework.dart:3666:14)
E/flutter ( 5452): #7      Element.updateChild (package:flutter/src/widgets/framework.dart:3418:18)
E/flutter ( 5452): #8      SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6186:14)
E/flutter ( 5452): #9      Element.inflateWidget (package:flutter/src/widgets/framework.dart:3666:14)
E/flutter ( 5452): #10     Element.updateChild (package:flutter/src/widgets/framework.dart:3418:18)
E/flutter ( 5452): #11     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4683:16)
E/flutter ( 5452): #12     Element.rebuild (package:flutter/src/widgets/framework.dart:4348:5)
E/flutter ( 5452): #13     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4636:5)
E/flutter ( 5452): #14     ComponentElement.mount (package:flutter/src/widgets/framework.dart:4631:5)
E/flutter ( 5452): #15     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3666:14)
E/flutter ( 5452): #16     Element.updateChild (package:flutter/src/widgets/framework.dart:3418:18)
E/flutter ( 5452): #17     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6186:14)
E/flutter ( 5452): #18     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3666:14)
E/flutter ( 5452): #19     Element.updateChild (package:flutter/src/widgets/framework.dart:3418:18)
E/flutter ( 5452): #20     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6186:14)
E/flutter ( 5452): #21     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3666:14)
E/flutter ( 5452): #22     Element.updateChild (package:flutter/src/widgets/framework.dart:3418:18)
E/flutter ( 5452): #23     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4683:16)
E/flutter ( 5452): #24     StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4831:11)
E/flutter ( 5452): #25     Element.rebuild (package:flutter/src/widgets/framework.dart:4348:5)
E/flutter ( 5452): #26     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4636:5)
E/flutter ( 5452): #27     StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4822:11)
E/flutter ( 5452): #28     ComponentElement.mount (package:flutter/src/widgets/framework.dart:4631:5)
E/flutter ( 5452): #29     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3666:14)
E/flutter ( 5452): #30     Element.updateChild (package:flutter/src/widgets/framework.dart:3418:18)
E/flutter ( 5452): #31     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6186:14)
E/flutter ( 5452): #32     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3666:14)
E/flutter ( 5452): #33     Element.updateChild (package:flutter/src/widgets/framework.dart:3418:18)
E/flutter ( 5452): #34     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6186:14)
E/flutter ( 5452): #35     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3666:14)
E/flutter ( 5452): #36     Element.updateChild (package:flutter/src/widgets/framework.dart:3418:18)
E/flutter ( 5452): #37     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4683:16)
E/flutter ( 5452): #38     StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4831:11)
E/flutter ( 5452): #39     Element.rebuild (package:flutter/src/widgets/framework.dart:4348:5)
E/flutter ( 5452): #40     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4636:5)
E/flutter ( 5452): #41     StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4822:11)
E/flutter ( 5452): #42     ComponentElement.mount (package:flutter/src/widgets/framework.dart:4631:5)
E/flutter ( 5452): #43     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3666:14)
E/flutter ( 5452): #44     Element.updateChild (package:flutter/src/widgets/framework.dart:3418:18)
E/flutter ( 5452): #45     C

the code which throws error is on line 83.

Has anyone had the same issue? I will really appreciate if someone gives me a good working example to use zxing2.

Note: I only need to use zxing2 not qr or bar code scanner

thanks

Answer 1

I know this is old, but it does not have a good answer. I can answer 2 parts of the question:

import 'package:zxing2/qrcode.dart';
import 'package:image/image.dart' as img;

...

class _QrCodeScannerState extends State<QrCodeScanner> {
  CameraController? controller;
  List<CameraDescription>? cameras;

  @override
  void initState() {
    super.initState();
    initializeCamera();  // this is fire and forget
  }

  Future<void> initializeCamera() async {
    cameras = await availableCameras();   // get available cameras
    if (cameras!.isNotEmpty) {
      controller = CameraController(cameras!.first, ResolutionPreset.high, imageFormatGroup: ImageFormatGroup.jpeg);
      await controller!.initialize();
      if (mounted) {
        setState(() {});  // we can now show the preview
        controller!.startImageStream(onLatestImage);    // and can start the imageStream
      }
    }
  }

  void onLatestImage(CameraImage image) {
    try {
      final barcode = decode(image.planes.first.bytes);
      print('$barcode');
    } catch (e) {
      print('Failed to decode image');
    }
  }

String decode(Uint8List fileBytes) {
  final image = img.decodeImage(fileBytes)!;

  LuminanceSource source = RGBLuminanceSource(
    image.width,
    image.height,
    image
      .convert(numChannels: 4)
      .getBytes(order: img.ChannelOrder.rgba)
      .buffer
      .asInt32List());
  final bitmap = BinaryBitmap(HybridBinarizer(source));
  final reader = QRCodeReader();
  return reader.decode(bitmap).text;
}

@override
Widget build(BuildContext context) {
  if (controller  == null || !controller!.value.isInitialized) {
    // important as we have to wait for the CameraController to be initialised
    return const Center(child: CircularProgressIndicator());
  }

  return Scaffold(
    body: Center(
      child: CameraPreview(controller!),
    ),
  );
}

The above does answer the first part - the correct use of the CameraController and getting a CameraImage, and the last past - how to use zxing2 to scan an image. However, I cannot guarantee to have answered the question of image conversion from CameraImage to something that zxing2 would understand.

Answer 2

I'v fixed this bug by adding call await controller.initialize(); before unawaited(controller.startImageStream((image) { at _onCameraSelected method.

But this example does not contain usage of zxing2...