我最近开始用flutter编程移动的应用程序。我在阅读文件时遇到问题。在实践中，当应用程序运行时，我将一个字符串写入一个文本文件（我也可以正确地读取它）。我的需要是每次访问应用程序时都从这个文件中读取;因此，在initState（）函数中，我调用readContent（）函数，但得到了以下消息：“FileSystemException：无法打开文件，路径=“/var/mobile/Containers/Data/Application/F8A5A202-45C9-47F6-93C9-E4BAE2AF3C7E/Documents/counter.txt”（OS错误：没有这样的文件或目录，errno = 2）"。你能帮帮我吗？
下面是我的代码：

Future<String> get _localPath async {
    final directory = await getApplicationDocumentsDirectory();
    print("directory path: "+directory.path);
    return directory.path;
  }

  Future<io.File> get _localFile async {
    final path = await _localPath;
    return io.File('$path/counter.txt');
  }

  String datas = "";

  //questa funzione viene richiamata all'avvio della schermata e serve per leggere il valore del flag checkSendingReport dal file
  @override
  void initState() {
    super.initState();
    readContent().then((String value) {
      print(value);
      setState(() {
        String data = value;

        List data_file_split = data.split("#");
        checkSendingReport = data_file_split[1];
        check_sending_report = data_file_split[1];
      });
    });
  }

  //Questa funzione serve per leggere il file locale scritto in precenza
  Future<String> readContent() async {
    try {
      final file = await _localFile;

      // Read the file
      String contents = await file.readAsString();
      //Returning the contents of the file
      return contents;

    } catch (e) {
      // If encountering an error, return
      return 'Error! '+e.toString();
    }
  }

  //questa funzione serve per scrivere il file locale
  Future<io.File> writeContent(datetime) async {
    final file = await _localFile;

    //Setto a true la variabile flag check_sending_report
    check_sending_report = true;

    //Creo la stringa da inserire nel file: composta da datetime#flag
    String data_file = datetime + "#" + check_sending_report.toString();

    // Write the file
    return file.writeAsString(data_file);
  }

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