Flutter FutureBuilder Not Updating

问题

I have a Flutter FutureBuilder that needs to be updated with new data given by the user. However, the UI elements in the FutureBuilder do not update and still contain the old values. I have checked through print statements that the new data is correctly loaded. The issue seems to be with FutureBuilder rebuilding the widget when the new data is loaded. Any help is appreciated.

Future<List<PollItem>> fetchPost(String loc) async {
  return new Future(() async {

    final response = await http
        .post(restip + '/getPosts',
        body: {"data": loc});

    if (response.statusCode == 200) {
      print(response.body);

      // If the call to the server was successful, parse the JSON
      // This function adds json to list
      PollItem.fromJson(json.decode(response.body));

      // list is a list of posts gathered based on the string criteria
      return list;
    } else {
      throw Exception('Failed to load polls');
    }
  });
}

class PollState extends State<Poll> {
  TextEditingController textc = new TextEditingController();

  static String dropDowntext = "City";
  String _name = "Search";
  final _names = [''];


  Widget build(BuildContext context) {

    print("dropdown"+dropDowntext);
    textc.text = _name;
    print(dropDowntext);
    return FutureBuilder<List<PollItem>>(
      future: fetchPost(dropDowntext),
      initialData: [PollItem()],
      builder: (context, snapshot) {
        if (snapshot.hasData) {
          print(snapshot.data[0].question);
          });
}

Here is my global file:

 List<PollItem> list = new List();
      factory PollItem.fromJson(Map<String, dynamic> json) {
        int len = json['length'];
        if(listNum!=len) {
          listNum = len;
          list.clear();
          for (int i = 0; i < len; i++) {
            list.add(PollItem(
              answer1: json[i.toString()]['answer1'],
              location: json[i.toString()]['location']

            )
            );
          }
        }
        }

回答1:

You don't need to create a Future object :

   Future<List<PollItem>> fetchPost(String loc) async {
    final response = await http.post(restip + '/getPosts',body: {"data": loc});

      if (response.statusCode == 200) {
        print(response.body);
        final data = json.decode(response.body);
        int len = data['length'];
        final List<PollItem> newList = List();
        for (int i = 0; i < len; i++) {
          newList.add(PollItem(
          answer1: data[i.toString()]['answer1'],
          location: data[i.toString()]['location']
            )
          );
        }

        print("new list size: ${newList.length}");

        return newList;
      } else {
        throw Exception('Failed to load polls');
      }
      return null;
  }

来源：https://stackoverflow.com/questions/54313596/flutter-futurebuilder-not-updating

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dart

Flutter