在Flutter中，将Firebase实时数据保存在本地存储json中，并从json填充列表视图

Question

在扑朔迷离中，我想从firebase实时数据库中获取数据并将其保存为json并保存在本地存储中，并从该json填充列表视图。如果数据库在firebase中进行了更新，那么Json应该会进行更新并反映在列表视图中。

DataSnapshot firebaseData;
File allnews_json;
Directory dir;
String allnews_filename = "allnews.json";
bool fileExists = false;

@override
  void initState() {
    super.initState();
     getApplicationDocumentsDirectory().then((Directory directory) {
          dir = directory;
          allnews_json = new File(dir.path + "/" + allnews_filename);
          fileExists = allnews_json.existsSync();
          if (fileExists) this.setState(() => fileContent = JSON.decode(allnews_json.readAsStringSync()));
        });


     FirebaseDatabase.instance.reference().child('news')
       .once()
       .then((onValue) {
          firebaseData = onValue.value;
          write(firebaseData);
       });
}

void write(DataSnapshot snapshot) async {

    print("Creating file!");
    File file = new File(dir.path + "/" + allnews_filename);
    file.createSync();

    final String key = snapshot.key;
    final String headline = snapshot.value['title'];
    final int news = snapshot.value['content'];
    String content = '{"$key":{"headline":"$headline","news":"$news"}}';
    file.writeAsStringSync(content);
  }

这是我到目前为止的代码。但这也有问题。