futureBuilder 无法从快照中获取数据

Question

 Future fetchData() async{
              List<Profile> list=[];
              list = await Firestore.instance
              .collection("users").getDocuments().then((querySnapshot){
               querySnapshot.documents.forEach((document) {
               list.add( Profile(
                    photos: [document['photoUrl'],],
                    name: document['nickname'],
                    age: 2,
                    distance: 2,
                    education: '3',
                    bio:"a"
                ));

            });
            print(list);
            print('list');
            return list; //[Instance of 'Profile']
        });
}



class _MainControllerState extends State<MainController> {







@override
Widget build(BuildContext context) {
  return new Container(
    padding: EdgeInsets.fromLTRB(0.0, 60.0, 0.0, 30.0),
    child: FutureBuilder(
      future: fetchData(),
      builder: (
        BuildContext context,
        AsyncSnapshot snapshot,
      ){
        if (snapshot.connectionState == ConnectionState.done ) {
           if (snapshot.data == null) {
             print(snapshot);//AsyncSnapshot<dynamic>(ConnectionState.done, null, null)
        return Text('no data');

      } else {
         print('matches');
              print(snapshot);
             List<Match> matches = snapshot.data
              .map((Profile profile) => Match(profile: profile))
              .toList();

          return CardStack(
            matchEngine: MatchEngine(matches: matches),
          );
      }

        } else if (snapshot.error) {
          print('matches1');
        } else {
          print('matches2');
        }
        return CardStack();
      },

    ),

  );
}

}

当我打印出列表时，我可以得到 ['Profile' 的实例]，但是当我在快照中打印数据时，我只能得到 AsyncSnapshot(ConnectionState.done, null, null) ，我该如何解决这个错误?

我尝试将 snapshot.connectionState == ConnectionState.done 更改为 snapshot.has 数据。但它不起作用。

Answer 1

 Future<List<Profile>> fetchData() async{
          List<Profile> list=[];
          list = await Firestore.instance
          .collection("users").getDocuments().then((querySnapshot)  async {
           querySnapshot.documents.forEach((document) {
           list.add( Profile(
                photos: [document['photoUrl'],],
                name: document['nickname'],
                age: 2,
                distance: 2,
                education: '3',
                bio:"a"
            ));

        });

        print(list);
        print('list');
        return list; //[Instance of 'Profile']
    });

        return list; //[Instance of 'Profile']
        }

Answer 2

FutureBuilder 不知道你从fetchData() 返回什么，所以你必须指定你将返回一个List<Profile>。因为没有类型的 Future 与 Future<void> 相同。

替换：

Future fetchData() async{...}

与：

Future<List<Profile>> fetchData() async{...}

类似地在FutureBuilder中指定

代替：

builder: (
    BuildContext context,
    AsyncSnapshot snapshot,
  ){...}

这样做：

builder: (
    BuildContext context,
    AsyncSnapshot<List<Profile>> snapshot,
  ){...}

希望这会有所帮助。