类“List”没有实例获取程序“documents”

Question

我正在尝试实现一个功能，其中应用程序以网格模式显示除当前用户之外的所有用户的详细信息。我一直试图将快照分配给_stream，然后在StreamBuilder（）中应用_stream值。但是它会抛出一个错误。

Database _database = Database();
Stream _stream;
String currentUserId;

@override
void initState() {
    getCurrentUserId(); //currentUserId gets its value here
    getAllUsers();
    super.initState();
}

getAllUsers() async {


 Stream<QuerySnapshot> snapshots = await _database.getAllUsers();
    
 _stream = snapshots.map((querySnapshot) => querySnapshot.documents.where((documentSnapshot)
          => documentSnapshot.data["userId"] != currentUserId
  ).toList())
}

//..

StreamBuilder(
stream: _stream,
builder: (context, snapshot) {
 if (snapshot.data != null)
 //..
 
}
//..
)

新：如果我将添加为QuerySnapshot，StreamBuilder中的快照将为空，而不是抛出异常。

// NEW
     _stream = snapshots.map((querySnapshot) => querySnapshot.documents.where((documentSnapshot)
     => documentSnapshot.data["userId"] != currentUserId
     ).toList() as QuerySnapshot);

数据库类

getAllUsers() async {
    return await _firestore.collection("users").snapshots();
}

例外

════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following NoSuchMethodError was thrown building StreamBuilder<dynamic>(dirty, state: _StreamBuilderBaseState<dynamic, AsyncSnapshot<dynamic>>#6e31f):
Class 'List<DocumentSnapshot>' has no instance getter 'documents'.
Receiver: Instance(length:2) of '_GrowableList'
Tried calling: documents

The relevant error-causing widget was: 
  StreamBuilder<dynamic> file:///Users/suriantosurianto/AndroidStudioProjects/apui/lib/fragments/home_fragment.dart:66:12
When the exception was thrown, this was the stack: 
#0      Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)
#1      _HomeFragmentState.build.<anonymous closure> (package:apui/fragments/home_fragment.dart:80:42)
#2      StreamBuilder.build (package:flutter/src/widgets/async.dart:509:81)
#3      _StreamBuilderBaseState.build (package:flutter/src/widgets/async.dart:127:48)
#4      StatefulElement.build (package:flutter/src/widgets/framework.dart:4619:28)
...
════════════════════════════════════════════════════════════════════════════════════════════════════

Answer 1

正如其他人所指出的，querySnapshot是一个列表

如果要返回类型为列表的流

_stream = snapshots
    .map<List<DocumentSnapshot>>((querySnapshot) => 
       querySnapshot.where((documentSnapshot) => 
          documentSnapshot.data["userId"] != currentUserId)
 );

Answer 2

// NEW
     _stream = snapshots.map((querySnapshot) => querySnapshot.documents.where((documentSnapshot)
     => documentSnapshot.data["userId"] != currentUserId
     ).toList() as QuerySnapshot);

这里的querySnapshot是一个列表

您可能必须使用querySnapshot。其中（）

Answer 3

我们不知道这个错误指向哪一行，但是如果我理解正确，原因可能是StreamBuilder属性stream的类型，它应该属于Stream类（参考）。

似乎流是使用列表方法（参考）从流创建的列表。我会尝试删除这个toList方法，看看会发生什么。

希望对大家有所帮助！