Flutter Barcode Scanner with Mobile Scanner

gistfile1.dart

import 'dart:async';

import 'package:flutter/material.dart';

import 'package:mobile_scanner/mobile_scanner.dart';


class ScannerWidget extends StatefulWidget {
  final String? title;
  final void Function(String value) onScan;
  const ScannerWidget({super.key, required this.onScan, this.title,});

  @override
  State<ScannerWidget> createState() => _ScannerState();
}

class _ScannerState extends State<ScannerWidget> with WidgetsBindingObserver {
  final MobileScannerController controller = MobileScannerController(
    autoStart: false,
    torchEnabled: false,
    useNewCameraSelector: true,
  );

  StreamSubscription<Object?>? _subscription;

  void _handleBarcode(BarcodeCapture barcodes) {
    if (mounted) {
      final String? value = barcodes.barcodes.firstOrNull?.displayValue?.trim();
      if(value != null) {
        widget.onScan(value);
        controller.stop();
      }
    }
  }

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);

    _subscription = controller.barcodes.listen(_handleBarcode);

    unawaited(controller.start());
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (!controller.value.isInitialized) {
      return;
    }

    switch (state) {
      case AppLifecycleState.detached:
      case AppLifecycleState.hidden:
      case AppLifecycleState.paused:
        return;
      case AppLifecycleState.resumed:
        _subscription = controller.barcodes.listen(_handleBarcode);

        unawaited(controller.start());
      case AppLifecycleState.inactive:
        unawaited(_subscription?.cancel());
        _subscription = null;
        unawaited(controller.stop());
    }
  }

  @override
  Widget build(BuildContext context) {
    final String title = widget.title ?? 'scan_your_badge';

    return Scaffold(
      backgroundColor: Colors.white,
      body: Stack(
        children: [
          Align(
            alignment: Alignment.center,
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.center,
              children: [
                Container(
                  width: 300,
                  height: 300,
                  alignment: Alignment.topCenter,
                  decoration: BoxDecoration(
                    border: Border.all(color: Colors.blue, width: 4),
                    color: Colors.blue,
                  ),
                  padding: const EdgeInsets.all(5),
                  child: MobileScanner(
                    controller: controller,
                    errorBuilder: (context, error, child) {
                      return Center(child: Text(error.toString()));
                    },
                    fit: BoxFit.fill,
                  ),
                ),
                const SizedBox(height: 25),
                Center(
                  child: Container(
                    padding: const EdgeInsets.symmetric(vertical: 8, horizontal: 15),
                    decoration: BoxDecoration(
                      color: Colors.white,
                      borderRadius: BorderRadius.circular(10),
                    ),
                    child: Text(
                      title,
                      style: const TextStyle(fontSize: 16),
                    ),
                  ),
                ),
              ]
            ),
          ),
          Align(
            alignment: Alignment.bottomCenter,
            child: Container(
              alignment: Alignment.center,
              height: 100,
              color: Colors.black.withOpacity(0.4),
              child: Row(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                children: [
                  ToggleFlashlightButton(controller: controller),
                ],
              ),
            ),
          ),
        ],
      ),
    );
  }

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

class ToggleFlashlightButton extends StatelessWidget {
  const ToggleFlashlightButton({required this.controller, super.key});

  final MobileScannerController controller;

  @override
  Widget build(BuildContext context) {
    return ValueListenableBuilder(
      valueListenable: controller,
      builder: (context, state, child) {
        if (!state.isInitialized || !state.isRunning) {
          return const SizedBox.shrink();
        }

        switch (state.torchState) {
          case TorchState.auto:
            return IconButton(
              color: Colors.white,
              iconSize: 32.0,
              icon: const Icon(Icons.flash_auto),
              onPressed: () async {
                await controller.toggleTorch();
              },
            );
          case TorchState.off:
            return IconButton(
              color: Colors.white,
              iconSize: 32.0,
              icon: const Icon(Icons.flash_off),
              onPressed: () async {
                await controller.toggleTorch();
              },
            );
          case TorchState.on:
            return IconButton(
              color: Colors.white,
              iconSize: 32.0,
              icon: const Icon(Icons.flash_on),
              onPressed: () async {
                await controller.toggleTorch();
              },
            );
          case TorchState.unavailable:
            return const Icon(
              Icons.no_flash,
              color: Colors.grey,
            );
        }
      },
    );
  }
}