Flutter：无法从模型获取数据到列表

问题描述 投票：0回答：2

我在模型类中遇到问题，无法将实时 Firebase 数据库中的数据提取到列表中，但收到 null。通过下面的图片进一步说明：

This 是要获取数据的图像。

这是一个模型类：

class Seller {
  var key;

  String address,
      businessType,
      description,
      fcm,
      joinTimeStamp,
      name,
      onlineStatus,
      picUrl,
      uuid;
  int blockByAdmin, completeOrders, rating;
  double lat;
  double lng;

  Seller(
      this.address,
      this.blockByAdmin,
      this.businessType,
      this.description,
      this.completeOrders,
      this.fcm,
      this.joinTimeStamp,
      this.lat,
      this.lng,
      this.name,
      this.onlineStatus,
      this.picUrl,
      this.rating,
      this.uuid);

  Seller.fromSnapshot(DataSnapshot snapshot)
      : key = snapshot.value,
        address = snapshot.value["address"],
        blockByAdmin = snapshot.value["blockByAdmin"],
        businessType = snapshot.value["businessType"],
        description = snapshot.value["description"],
        completeOrders = snapshot.value["completeOrders"],
        fcm = snapshot.value["fcm"],
        joinTimeStamp = snapshot.value["joinTimeStamp"],
        lat = snapshot.value["lat"],
        lng = snapshot.value["lng"],
        name = snapshot.value["name"],
        onlineStatus = snapshot.value["onlineStatus"],
        picUrl = snapshot.value["picUrl"],
        rating = snapshot.value["rating"],
        uuid = snapshot.value["uuid"];

  toJson() {
    return {
      'address': address,
      'blockByAdmin': blockByAdmin,
      'businessType': businessType,
      'description': description,
      'completeOrders': completeOrders,
      'fcm': fcm,
      'joinTimeStamp': joinTimeStamp,
      'lat': lat,
      'lng': lng,
      'name': name,
      'onlineStatus': onlineStatus,
      'picUrl': picUrl,
      'rating': rating,
      'uuid': uuid,
    };
  }
}

这是一个我们使用模型类并在列表长度处获取 null 的类：

 class Body extends StatefulWidget {
    
      @override
      _BodyState createState() => _BodyState();
    }
    
    class _BodyState extends State<Body> {
      final urlImage =
          'https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSPlqk-tNmFTjT7q_edAjaYLU5qf2cFUM9vfrweUbqnS_58LqF7AMp67KVdslIubuzy9b4&usqp=CAU';
      final _database = FirebaseDatabase.instance.reference().child('kjobhee');
      List<Seller> _sellerList;
      StreamSubscription<Event> _onTodoAddedSubscription;
      Query _query;
    
      @override
      void initState() {
        super.initState();
       
        _activateListeners();
      }
   
      void _activateListeners() {
        _query = _database.child('seller');
        _onTodoAddedSubscription = _query.onValue.listen(onEntryAdded);
      }
    
      onEntryAdded(Event event) {
        setState(() {
          _sellerList.add(Seller.fromSnapshot(event.snapshot));
          print(_sellerList);
        });
      }
    
      @override
      Widget build(BuildContext context) {
        return Scaffold(
          appBar: AppBar(
            backgroundColor: kPrimaryColor,
          ),
          drawer: NavigationDrawer(),
          body: RefreshIndicator(
            onRefresh: () => _buildBuyerProfile(),
            child: _sellerList.length > 0
                ? ListView.builder(
                    shrinkWrap: true,
                    itemCount: _sellerList.length,
                    itemBuilder: (BuildContext context, int index) {
                      String key = _sellerList[index].key;
                      String address = _sellerList[index].address;
                      int blockByAdmin = _sellerList[index].blockByAdmin;
                      String businessType = _sellerList[index].businessType;
                      String description = _sellerList[index].description;
                      int completeOrders = _sellerList[index].completeOrders;
                      String fcm = _sellerList[index].fcm;
                      String joinTimeStamp = _sellerList[index].joinTimeStamp;
                      double lat = _sellerList[index].lat;
                      double lng = _sellerList[index].lng;
                      String name = _sellerList[index].name;
                      String onlineStatus = _sellerList[index].onlineStatus;
                      String picUrl = _sellerList[index].picUrl;
                      int rating = _sellerList[index].rating;
                      String uuid = _sellerList[index].uuid;
                      print(key +
                          '/' +
                          address +
                          '/' +
                          blockByAdmin.toString() +
                          '/' +
                          businessType +
                          '/' +
                          description +
                          '/' +
                          completeOrders.toString() +
                          '/' +
                          fcm +
                          '/' +
                          joinTimeStamp +
                          '/' +
                          lat.toString() +
                          '/' +
                          lng.toString() +
                          '/' +
                          name +
                          '/' +
                          onlineStatus +
                          '/' +
                          picUrl +
                          '/' +
                          rating.toString() +
                          '/' +
                          uuid);
                      return _buildBuyerProfile();
                    })
                : Center(
                    child: CircularProgressIndicator(),
                  ),
          ),
        );
      }

我将非常感谢任何用户的帮助。

firebase flutter dart firebase-realtime-database
2个回答
2
投票

这里您需要考虑一些事情：

  1. 您需要确保从 Firebase 获取数据，尝试在日志中打印它并检查您是否正在接收数据。

  2. 您需要管理您的用户界面，考虑到当屏幕首次加载时您的数据将不存在，这意味着您的变量 _sellerList 将为空。因此需要检查您的代码中缺少哪些内容。

  3. 如果您没有从 firebase 获取数据，但我认为配置已正确完成，那么您可以使用与我使用的代码相同的代码来获取数据：

    Future<void> fetchProducts() async {
await FirebaseFirestore.instance
    .collection(FirebaseCollectionConst.productsCollection)
    .get()
    .then((QuerySnapshot productsData) {
  _products = [];
      productsData.docs.forEach((element) {
        _products.insert(0, Product(
            id: element.get('productId'),
            title: element.get('productTitle'),
            description: element.get('productDescription'),
            price: double.parse(element.get('price')),
            imageUrl: element.get('productImage'),
            brand: element.get('productBrand'),
            productCategoryName: element.get('productCategory'),
            quantity: int.parse(element.get('productQuality')),
            isFavourite: false,
            isPopular: true));
      });
});

    }

在这里，我获取产品集合并将其收集到扩展 ChangeNotifier 类的类成员中，并在 Provider 的帮助下显示该数据。

0
投票

我认为你需要在模型中处理 null

像这样-

Seller.fromSnapshot(DataSnapshot snapshot)
          : key = snapshot.value,
            address = snapshot.value["address"] ?? '',
            blockByAdmin = snapshot.value["blockByAdmin"] ?? '',
            businessType = snapshot.value["businessType"] ?? '',
            description = snapshot.value["description"] ?? '',
            completeOrders = snapshot.value["completeOrders"] ?? '',
            fcm = snapshot.value["fcm"] ?? '',
            joinTimeStamp = snapshot.value["joinTimeStamp"] ?? '',
            lat = snapshot.value["lat"] ?? '',
            lng = snapshot.value["lng"] ?? '',
            name = snapshot.value["name"] ?? '',
            onlineStatus = snapshot.value["onlineStatus"] ?? '',
            picUrl = snapshot.value["picUrl"] ?? '',
            rating = snapshot.value["rating"] ?? '',
            uuid = snapshot.value["uuid"] ?? '';

也许你的问题会得到解决。我没试过，但你可以！

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