Flutter Firebase：错误状态：快照既没有数据也没有错误

Question

我正在尝试从 table 产品中获取 P_ID 添加到购物车的特定产品现在下面的代码运行良好但只检索一个元素

final Stream<QuerySnapshot> cart = FirebaseFirestore.instance
        .collection('products')
        .where('pid', isEqualTo: cartitems[0])
        .snapshots();

但是当我这样做时它不起作用

Stream<QuerySnapshot>? cart;
for (var i = 0; i < cartitems.length; i++) {
  cart = FirebaseFirestore.instance
      .collection('products')
      .where('pid', isEqualTo: cartitems[i])
      .snapshots();
}

它给我这个错误

The following StateError was thrown building StreamBuilder<QuerySnapshot<Object?>>(dirty, state: _StreamBuilderBaseState<QuerySnapshot<Object?>, AsyncSnapshot<QuerySnapshot<Object?>>>#9ea5d): Bad state: Snapshot has neither data nor error

The relevant error-causing widget was: StreamBuilder<QuerySnapshot<Object?>> StreamBuilder

Answer 1

您可以尝试使用 Stream Builder 来代替 for 循环来达到相同的效果。 Stream Builder 将自动取出您存储在 firebase 中的所有购物车项目。要消除快照错误，请执行以下 if 语句。

final CollectionReference cart = FirebaseFirestore.instance.collection('products');
child: StreamBuilder(
        stream: cart
            .where('pid', isEqualTo: cartitems)
            .snapshots();
        builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) { 
        if (!snapshot.hasData) {
            return const Text('Loading...');
        } 
        if (snapshot.hasError) {
            return const Text('Something went wrong.');
        }

Flutter Firebase：错误状态：快照既没有数据也没有错误

Flutter Firebase: Bad state: Snapshot has neither data nor error

firebase

firebase-realtime-database

flutter