flutter - 在 StreamBuilder 中渲染 ListView.ListTile

Question

我有一个 Flutter 应用程序，我试图在 StreamBuilder 中渲染一个 ListTile。

加载应用程序时出现此错误：

'Future<List>' 类型不是 'List' 类型的子类型

neabyComp() 函数片段：

Stream nearbyComp() async* {
    var pos = await location.getLocation();

    GeoFirePoint point =
        geo.point(latitude: pos.latitude, longitude: pos.longitude);
    final CollectionReference users =
        _firebaseFirestore.collection("Companies");

    double radius = 10;
    String field = 'location';

    Stream<List<DocumentSnapshot>> stream = geo
        .collection(collectionRef: users)
        .within(center: point, radius: radius, field: field, strictMode: true);

    yield stream;
  }

这是错误来自的 StreamBuilder 的代码片段：

Container(
            child: StreamBuilder(
              stream: nearbyComp(),
              builder: (BuildContext context, AsyncSnapshot snapshot) {
                if (snapshot.hasError) {
                  return Text('Something went wrong');
                }
                if (snapshot.connectionState == ConnectionState.waiting) {
                  return Text("Loading");
                }
                return Container(
                  child: new ListView(
                    children: snapshot.data.map((document) {
                      // Adding snapshot.data.map<Widget> also returns error "Future<List<Widget>> is not a subtype of type List<Widget>"
                      return new ListTile(
                        title: new Text(document['companyName']),
                        subtitle: new Image.network(document['url']),
                      );
                    }).toList(),
                  ),
                );
              },
            ),
          ),

标签： flutterlistviewstream-builder

Answer 1

如果有人遇到这个问题，这里是@pskink 提供的解决方案（查找代码片段上的注释）：

Stream nearbyComp() async* {
    var pos = await location.getLocation();

    GeoFirePoint point =
        geo.point(latitude: pos.latitude, longitude: pos.longitude);
    final CollectionReference users =
        _firebaseFirestore.collection("Companies");

    double radius = 10;
    String field = 'location';

    Stream<List<DocumentSnapshot>> stream = geo
        .collection(collectionRef: users)
        .within(center: point, radius: radius, field: field, strictMode: true);

    yield* stream; // In this line, add the * after yield
  }

另一部分在这里：

Container(
            child: StreamBuilder(
              stream: nearbyComp(),
              builder: (BuildContext context, AsyncSnapshot snapshot) {
                if (snapshot.hasError) {
                  return Text('Something went wrong');
                }
                if (snapshot.connectionState == ConnectionState.waiting) {
                  return Text("Loading");
                }
                return Container(
                  child: new ListView(
                    children: snapshot.data.map((document) {
                      // Add snapshot.data.map<Widget> 
                      return new ListTile(
                        title: new Text(document['companyName']),
                        subtitle: new Image.network(document['url']),
                      );
                    }).toList(),
                  ),
                );
              },
            ),
          ),