我正在尝试创建一个包含3个选项卡的UI屏幕。 LatestItem，ReviewItem和Profile。但是，最近项目小部件中存在一些后端问题。显示错误：类'QuerySnapshot'没有实例获取器'data'。 附言：整个代码很大，因此我为整个代码共享了一个文档：https://docs.google.com/document/d/1qs4ajPJ0DBjserBJ3iBZmPXPz1zTP7tIYSh8vceVQn8/edit?usp=sharing LatestItems（）：
Widget RecentItems() {
return Padding(
padding: const EdgeInsets.all(10.0),
child: StreamBuilder(
stream: Firestore.instance
.collection("users")
.document(uid)
.collection("recent")
.snapshots(),
builder: (context, snapshot) {
print(snapshot.data);
List orders = List.from(Map.from(snapshot.data.data)['orders']);
Map order;
for (int i = 0; i < orders.length; i++) {
if (orders[i]['orderId'] == widget.map['orderId'] &&
orders[i]['homemaker'] == widget.map['homemaker']) {
order = orders[i];
break;
}
}
if (snapshot.data.isEmpty) {
return Center(
child:
Text("OOPS, Looks like no one is serving!"));
}
print(order);
if (snapshot.connectionState == ConnectionState.waiting) {
return Center(child: CircularProgressIndicator());
} else if (snapshot.hasData) {
print(snapshot.data.documents[0].data);
return Container(
height: 400,
child: ListView.builder(
itemCount: snapshot.data.documents.length,
itemBuilder: (BuildContext context, int index) {
return Container(
margin: EdgeInsets.all(10.0),
width: MediaQuery
.of(context)
.size
.width,
height: 85,
decoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.circular(10.0),),
child: Padding(
padding: const EdgeInsets.all(10.0),
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Row(
children: <Widget>[
Expanded(child: Text(
"${snapshot.data.documents[index]
.data["dishname"]}", style: TextStyle(
fontSize: 15,
fontWeight: FontWeight.bold),)),
//Icon: how to access if food is veg or not
],
),
// SizedBox(height:5),
Row(
children: <Widget>[
Expanded(child: Text(
"${snapshot.data.documents[index]
.data["homemaker"]}",
style: TextStyle(fontSize: 10),)),
Text("${snapshot.data.documents[index]
.data["rating"]}",
style: TextStyle(fontSize: 15)),
Icon(
Icons.star, color: Colors.yellow.shade800,
size: 20,)
],
),
SizedBox(height: 5),
//How to access order date
Text(
"Ordered ${DateTime
.parse(order['order_placed_at']
.toDate()
.toString())
.day}/${DateTime
.parse(order['order_placed_at']
.toDate()
.toString())
.month}/${DateTime
.parse(order['order_placed_at']
.toDate()
.toString())
.year}}",
style: TextStyle(fontSize: 15.0,
fontWeight: FontWeight.bold),
),
],
),
),
);
}),
);
} //
}),
);
}
错误消息是：
The getter 'data' was called on null.
Receiver: null
Tried calling: data
The relevant error-causing widget was:
StreamBuilder<QuerySnapshot> file:///C:/Flutter/Naniz_eats/lib/UserProfilePage.dart:434:14
════════════════════════════════════════════════════════════════════════════════════════════════════
I/flutter (28940): Instance of 'QuerySnapshot'
════════ (3) Exception caught by widgets library ═══════════════════════════════════════════════════
Class 'QuerySnapshot' has no instance getter 'data'.
Receiver: Instance of 'QuerySnapshot'
Tried calling: data
The relevant error-causing widget was:
StreamBuilder<QuerySnapshot> file:///C:/Flutter/Naniz_eats/lib/UserProfilePage.dart:434:14
答案 0 :(得分：0)
可能有几件事或所有原因导致
print第一行中的builder。如果snapshot确实为空，则您已经在调用数据而无需先检查其是否为空。
snapshot.data.data，我认为是builder
您在不首先检查snapshot.hasData，snapshot.data.documents.length != 0以确保您没有对空快照进行操作的情况下对快照进行操作的事实。
您还应该能够通过按以下错误消息来专门检查导致错误的行，其中一条错误消息应包含指向特定行的链接（问题中未显示，应在较长的字符之间一堆错误消息）
答案 1 :(得分：0)
此代码：
Firestore.instance
.collection("users")
.document(uid)
.collection("recent")
.snapshots()
返回类型为Stream的{{1}}，问题出在这里：
QuerySnapshot代码 List orders = List.from(Map.from(snapshot.data.data)['orders']);
将返回snapshot.data的实例，而QuerySnapshot不包含名为QuerySnapshot的实例变量。因此，如果要列出文档列表，则必须执行以下操作：
data