qr_code_reader.dart

class SomeStatefulWidget extends StatefulWidget {
    @override
  _SomeStatefulWidgetState createState() => _SomeStatefulWidgetState();
}

class _SomeStatefulWidgetState extends State<SomeStatefulWidget> {
  static const platform = const MethodChannel('your.app.identifier/qrcode');
  final PermissionsManager _permissionsManager = PermissionsManager();
  bool _iOSDidSendQRCode = false;

  @override
  void initState() {
    super.initState();
    platform.setMethodCallHandler((MethodCall methodCall) {
      switch (methodCall.method) {
        case 'cameraPermissionChanged': // カメラの権限が変わった時は再描画
          setState(() {

          });
          return null;
        case 'resumeScan': // 画面のスキャンを再開
          _iOSDidSendQRCode = false;
          this.controller.resumeCamera();
          return null;
        default:
          throw MissingPluginException('notImplemented');
      }
    });
  }
}