Question

final databaseReference = Firestore.instance.collection("classrooms");
bool hany = false;
var names = new Map<String, dynamic>();
List nevek = [];
List IDS = [];

Future<void> getclasses() async {
  QuerySnapshot snapshot = await databaseReference.getDocuments();

  snapshot.documents.forEach((f) {
    IDS.add(f.documentID);
    x = (f.data.length);
    names.addAll(f.data);
    for (int i = 0; i < names.values.toList().length / x; i++) {
      nevek.add(names.values.toList()[i + 1]);
    }
  });
}

class ScrollableClassroom extends StatefulWidget {
  @override
  _ScrollableClassroomState createState() => _ScrollableClassroomState();
}

class _ScrollableClassroomState extends State<ScrollableClassroom> {
  @override
  void initState() {
    super.initState();
    IDS = [];
    names.clear();
    getclasses();
  }

  Widget build(BuildContext context) {
    print(nevek);
    print(IDS);

    return WillPopScope(
      onWillPop: () async => false,
      child: Scaffold(
        appBar: AppBar(
          centerTitle: true,
          title: Text("Osztályok"),
          leading: Padding(
              padding: const EdgeInsets.only(left: 5.0),
              child: IconButton(
                  icon: Icon(Icons.exit_to_app, color: Colors.black38),
                  onPressed: () {
                    authService.signOut();
                    authService.loggedIn = false;
                    Navigator.push(
                        context,
                        MaterialPageRoute(
                            builder: (context) => GoogleSignUp()));
                  })),
          actions: <Widget>[
            Padding(
                padding: const EdgeInsets.only(right: 5.0),
                child: Row(
                  children: <Widget>[
                    IconButton(
                        icon: Icon(Icons.add_circle_outline,
                            color: Colors.black38),
                        onPressed: null),
                    IconButton(
                        icon: Icon(Icons.search, color: Colors.black38),
                        onPressed: null),
                  ],
                )),
          ],
        ),
        body: ListView.builder(
          itemCount: nevek.length,
          itemBuilder: (context, index) {
            return Card(
              child: ListTile(
                onTap: () {
                  id = IDS[index];
                  Navigator.push(context,
                      MaterialPageRoute(builder: (context) => InClassRoom()));
                },
                title: Text(nevek[index]),
              ),
            );
          },
        ),
      ),
    );
  }
}

在Listview中，它第一次不显示任何内容，但是在热重新加载后，它可以正常工作。但是，如果我进行第二次热重装，它将显示所有内容，但是显示两次。另一种情况是，当我按下应用程序栏左侧的后退按钮时，它将带您进入登录屏幕。如果您是第一次从登录屏幕返回，那么很好，但是如果再次执行此操作，它将再次显示所有内容。然后那三遍，等等。

Answer 1

首先，在映射完文档后，您缺少setState

将状态变量保留在状态类中

Answer 2

尝试以下代码：

class ScrollableClassroom extends StatefulWidget {
  @override
  _ScrollableClassroomState createState() => _ScrollableClassroomState();
}

class _ScrollableClassroomState extends State<ScrollableClassroom> {

//moved from the Widget class
final databaseReference = Firestore.instance.collection("classrooms");
bool hany = false;
var names = new Map<String, dynamic>();
List nevek = [];
List IDS = [];

Future<void> getclasses() async {
  QuerySnapshot snapshot = await databaseReference.getDocuments();

  snapshot.documents.forEach((f) {
    IDS.add(f.documentID);
    x = (f.data.length);
    names.addAll(f.data);
    for (int i = 0; i < names.values.toList().length / x; i++) {
      nevek.add(names.values.toList()[i + 1]);
    }
  });
setState((){}); // <- this line tells the StetefulWidget that it's state has been changed and it needs to rebuild
}
...(the rest of the state class)

Flutter Firebase不会第一次加载数据，但在下一次尝试时会多次加载数据

2 个答案: