Crash when return from qr code scanner page to its callee page

[superymk]

Hi,

Thanks for your great work in this lib!

I'd like to pop a page to take a qr code and return the result to the caller page. I created the callee page with the MobileScannerController. However, it crashes once the page scanned a valid qr code.

What could be the cause?

Thanks a lot!

import 'dart:async';
import 'dart:typed_data';

import 'package:flutter/material.dart';
import 'package:mobile_scanner/mobile_scanner.dart';

class MobileScannerPage extends StatefulWidget {
  @override
  _MobileScannerPageState createState() => _MobileScannerPageState();
}

class _MobileScannerPageState extends State<MobileScannerPage> {
  Barcode? result;
  final MobileScannerController cameraController = MobileScannerController(
    torchEnabled: true, useNewCameraSelector: true,
    formats: [BarcodeFormat.qrCode],
    // facing: CameraFacing.front,
    // detectionSpeed: DetectionSpeed.normal
    // detectionTimeoutMs: 1000,
    // returnImage: false,
  );

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Mobile Scanner'),
        actions: [
          IconButton(
            color: Colors.white,
            icon: ValueListenableBuilder(
              valueListenable: cameraController.torchState,
              builder: (context, state, child) {
                switch (state as TorchState) {
                  case TorchState.off:
                    return const Icon(Icons.flash_off, color: Colors.grey);
                  case TorchState.on:
                    return const Icon(Icons.flash_on, color: Colors.yellow);
                }
              },
            ),
            iconSize: 32.0,
            onPressed: () => cameraController.toggleTorch(),
          ),
          IconButton(
            color: Colors.white,
            icon: ValueListenableBuilder(
              valueListenable: cameraController.cameraFacingState,
              builder: (context, state, child) {
                switch (state as CameraFacing) {
                  case CameraFacing.front:
                    return const Icon(Icons.camera_front);
                  case CameraFacing.back:
                    return const Icon(Icons.camera_rear);
                }
              },
            ),
            iconSize: 32.0,
            onPressed: () => cameraController.switchCamera(),
          ),
        ],
      ),
      body: MobileScanner(
        // fit: BoxFit.contain,
        controller: cameraController,
        onDetect: (capture) {
          final List<Barcode> barcodes = capture.barcodes;
          // // final Uint8List? image = capture.image;
          // // for (final barcode in barcodes) {
          // //   debugPrint('Barcode found! ${barcode.rawValue}');
          // // }

          // if (barcodes.isNotEmpty) {
          //   // Uint8List result = Uint8List.fromList(barcodes[0].rawBytes);

          //   // Navigator.pop(context, barcodes.first.rawBytes);  // Close the scanner and return the image

          //   // Navigator.pop(context, barcodes[0].rawBytes);  // Close the scanner and return the image
          //   ValueUtil.set_val1(barcodes[0].rawBytes);
          //   ValueUtil.set_val2(true);

          //   barcodes.clear();

          //   // Navigator.pop(context);
          //   Future.delayed(Duration.zero, () {
          //     Navigator.pop(context);
          //     // Navigator.pop(context, barcodes[0].rawBytes);
          //   });
          // } else {
          //   ValueUtil.set_val2(false);
          // }

          // Tried several ways to return the result.
          if (barcodes.isNotEmpty) {
              // ValueUtil.set_val1(barcodes[0].rawBytes);
              // ValueUtil.set_val2(true);
              Navigator.pop(context);
          } else {
            // ValueUtil.set_val2(false);
          }
        },
      ),
    );
  }

  @override
  Future<void> dispose() async {
    // WidgetsBinding.instance.removeObserver(this);
    // unawaited(_subscription?.cancel());
    // _subscription = null;

    super.dispose();

    // await cameraController.dispose();
    cameraController.dispose();
  }
}

The caller page:

@override
  Widget build(BuildContext context) {
    ....
    
    return Scaffold(
      body: Column(
        children: [
          Container(
            height: buttonContainerHeight,
            padding: const EdgeInsets.symmetric(vertical: 20.0),
            child: GestureDetector(
              onTap: () async {
                // When switching pages, add a delay to the next start call.
                // Otherwise the camera will start before the next page is displayed.
                await Future.delayed(
                    const Duration(seconds: 1, milliseconds: 500));

                var res = await Navigator.push(
                    context,
                    MaterialPageRoute(
                      builder: (context) =>
                          MobileScannerPage(), // Changed to MobileScannerPage
                    ));
                if (res != null) {
                  // debugPrint('Barcode found! ${res.lengthInBytes}');
                  // updateButtonContent("${res.lengthInBytes}");
                }
                // if (res != null && res is String) {
                //   updateButtonContent(res);
                // }
              },

[superymk]

Problem solved by modifying onDetect():

if (barcodes.isNotEmpty && mounted) {
            cameraController.stop().then((_) {
              Uint8List? result = barcodes[0].rawBytes;
              barcodes.clear();

              Navigator.pop(context, result); // You can return any data you need here
            });

Please let me know any other suggestions. Thanks!