firebase - futureBuilder无法从快照获取数据

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)，如何解决该错误？

我试图将snapshot.connectionState == ConnectionState.done更改为snapshot.has数据。但它不起作用。

Answer 1

FutureBuilder不知道从fetchData()返回什么，因此必须指定要返回的List<Profile>。由于没有类型的Future与Future<void>相同。

更换:

Future fetchData() async{...}

与:

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

同样，用 FutureBuilder分隔

代替:

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

做这个:

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

希望这可以帮助。