Flutter 中监听输入字符串的事件

我有一部连接了条形码扫描仪的手机。扫描仪读取条形码时，必须将其记录在屏幕上所需的字段中。如果该字段最初是通过点击它来激活的，则此方法有效。但扫描的条形码必须适合该字段，即使它尚未被用户激活。也就是说，您需要创建某种事件，期望某些文本到达并在自动字段中输入此文本。请告诉我如何做到这一点？或者也许已经有现成的插件？

更新1：扫描字段时，需要barcode写入一个字符串，即使该字段未激活（未选中焦点）

class DocumentsScreen extends StatefulWidget {
  final DocumentsModel documentInfo;

  const DocumentsScreen({Key key, this.documentInfo})
      : super(key: key);

  @override
  _DocumentsScreen createState() =>
      _DocumentsScreen(documentInfo);
}

class _DocumentsScreen extends State<DocumentsScreen> {
  final DocumentsModel documentInfo;

  _DocumentsScreen(this.documentInfo);

  TextEditingController barcode = new TextEditingController();
  FocusNode barcodeFocus = new FocusNode();

  DocumentInfoModel arrivalDocumentInfo =
      new DocumentInfoModel(documentItems: new List<DocumentItems>());
  int _sortIndex;
  bool _sortAscending = false;

  @override
  void initState() {
    onRefresh();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new TextLeft(
            '${documentInfo.documentName}', TextStyleBase.whiteSize15),
      ),
      body: new RefreshIndicator(
          child: new Column(
            children: <Widget>[
              new Row(
                children: <Widget>[
                  new Expanded(
                    child: new TextField(
                      controller: barcode,
                      focusNode: barcodeFocus,
                      decoration: new InputDecoration(
                          hintText: 'Просканируйте штрих-код'),
                      onEditingComplete: () {
                        if (barcode.text != '') {
                          // Some code...
                        }
                      },
                    ),
                  ),
                  new VoidIconButton(Icons.clear, Colors.red, () {
                    barcode.clear();
                  }),
                ],
              ),
              new Expanded(
                child: new ListView(
                  children: <Widget>[
                    // Some code...
                  ],
                ),
              ),
              // Some code...
            ],
          ),
          onRefresh: onRefresh),
    );
  }

  Future onRefresh() async {
    documentService
        .documentItemsByDocumentId(documentInfo.documentId)
        .then((document) {
      setState(() {
        arrivalDocumentInfo = document;
        barcode.clear();
        barcodeFocus.requestFocus();
      });
    });
  }

  // Some code...
}