qr_code_scanner/example/lib/main.dart

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

void main() => runApp(MaterialApp(home: QRViewExample()));

const flashOn = 'FLASH ON';
const flashOff = 'FLASH OFF';
const frontCamera = 'FRONT CAMERA';
const backCamera = 'BACK CAMERA';

class QRViewExample extends StatefulWidget {
  const QRViewExample({
    Key key,
  }) : super(key: key);

  @override
  State<StatefulWidget> createState() => _QRViewExampleState();
}

class _QRViewExampleState extends State<QRViewExample> {
  var qrText = '';
  var flashState = flashOn;
  var cameraState = frontCamera;
  QRViewController controller;
  final GlobalKey qrKey = GlobalKey(debugLabel: 'QR');

  @override
  void reassemble() {
    super.reassemble();
    controller.pauseCamera();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        children: <Widget>[
          Expanded(flex: 4, child: _buildQrView(context)),
          Expanded(
            flex: 1,
            child: FittedBox(
              fit: BoxFit.contain,
              child: Column(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                children: <Widget>[
                  Text('This is the result of scan: $qrText'),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.center,
                    crossAxisAlignment: CrossAxisAlignment.center,
                    children: <Widget>[
                      Container(
                        margin: EdgeInsets.all(8),
                        child: RaisedButton(
                          onPressed: () {
                            if (controller != null) {
                              controller.toggleFlash();
                              if (_isFlashOn(flashState)) {
                                setState(() {
                                  flashState = flashOff;
                                });
                              } else {
                                setState(() {
                                  flashState = flashOn;
                                });
                              }
                            }
                          },
                          child:
                              Text(flashState, style: TextStyle(fontSize: 20)),
                        ),
                      ),
                      Container(
                        margin: EdgeInsets.all(8),
                        child: RaisedButton(
                          onPressed: () {
                            if (controller != null) {
                              controller.flipCamera();
                              if (_isBackCamera(cameraState)) {
                                setState(() {
                                  cameraState = frontCamera;
                                });
                              } else {
                                setState(() {
                                  cameraState = backCamera;
                                });
                              }
                            }
                          },
                          child:
                              Text(cameraState, style: TextStyle(fontSize: 20)),
                        ),
                      )
                    ],
                  ),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.center,
                    crossAxisAlignment: CrossAxisAlignment.center,
                    children: <Widget>[
                      Container(
                        margin: EdgeInsets.all(8),
                        child: RaisedButton(
                          onPressed: () {
                            controller?.pauseCamera();
                          },
                          child: Text('pause', style: TextStyle(fontSize: 20)),
                        ),
                      ),
                      Container(
                        margin: EdgeInsets.all(8),
                        child: RaisedButton(
                          onPressed: () {
                            controller?.resumeCamera();
                          },
                          child: Text('resume', style: TextStyle(fontSize: 20)),
                        ),
                      )
                    ],
                  ),
                ],
              ),
            ),
          )
        ],
      ),
    );
  }

  bool _isFlashOn(String current) {
    return flashOn == current;
  }

  bool _isBackCamera(String current) {
    return backCamera == current;
  }

  Widget _buildQrView(BuildContext context) {
    // To ensure the Scanner view is properly sizes after rotation
    // we need to listen for Flutter SizeChanged notification and update controller
    return NotificationListener<SizeChangedLayoutNotification>(
        onNotification: (notification) {
          Future.microtask(() => controller?.updateDimensions(qrKey));
          return false;
        },
        child: SizeChangedLayoutNotifier(
            key: const Key('qr-size-notifier'),
            child: QRView(
              key: qrKey,
              onQRViewCreated: _onQRViewCreated,
              overlay: QrScannerOverlayShape(
                borderColor: Colors.red,
                borderRadius: 10,
                borderLength: 30,
                borderWidth: 10,
                cutOutSize: 300,
              ),
            )));
  }

  void _onQRViewCreated(QRViewController controller) {
    this.controller = controller;
    controller.scannedDataStream.listen((scanData) {
      setState(() {
        qrText = scanData;
      });
    });
  }

  @override
  void dispose() {
    controller.dispose();
    super.dispose();
  }
}