如何在streambuilder中查询firestore文档并更新listview
我试图从名为“posts”的Firestore集合中检索帖子,该集合包含帖子创建者的用户ID和帖子描述,这可以通过使用StreamBuilder和FutureBuilder实现(不可取,因为它只获取一次快照,并且不会在字段更改时更新) 但是,我想查询另一个名为“users”的集合,并使用post creator的userID检索与该userID匹配的文档 这是我的第一个方法:如何在streambuilder中查询firestore文档并更新listview,listview,dart,flutter,google-cloud-firestore,Listview,Dart,Flutter,Google Cloud Firestore,我试图从名为“posts”的Firestore集合中检索帖子,该集合包含帖子创建者的用户ID和帖子描述,这可以通过使用StreamBuilder和FutureBuilder实现(不可取,因为它只获取一次快照,并且不会在字段更改时更新) 但是,我想查询另一个名为“users”的集合,并使用post creator的userID检索与该userID匹配的文档 这是我的第一个方法: StreamBuilder<QuerySnapshot>( stream:Firestore.insta
StreamBuilder<QuerySnapshot>(
stream:Firestore.instance.collection("posts").snapshots(),
builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
if (!snapshot.hasData) {
return Center(
child: _showProgressBar,
);
}
List<DocumentSnapshot> reversedDocuments = snapshot.data.documents.reversed.toList();
return ListView.builder(
itemCount: reversedDocuments.length,
itemBuilder: (BuildContext context, int index){
String postAuthorID = reversedDocuments[index].data["postAuthorID"].toString();
String postAuthorName = '';
Firestore.instance.collection("users")
.where("userID", isEqualTo: postAuthorID).snapshots().listen((dataSnapshot) {
print(postAuthorName = dataSnapshot.documents[0].data["username"]);
setState(() {
postAuthorName = dataSnapshot.documents[0].data["username"];
});
});
String desc = reversedDocuments[index].data["post_desc"].toString();
return new ListTile(
title: Container(
child: Row(
children: <Widget>[
Expanded(
child: Card(
child: new Column(
children: <Widget>[
ListTile(
title: Text(postAuthorName, //Here, the value is not changed, it holds empty space.
style: TextStyle(
fontSize: 20.0,
),
),
subtitle: Text(desc),
),
)
StreamBuilder(
流:Firestore.instance.collection(“posts”).snapshots(),
生成器:(BuildContext上下文,异步快照){
如果(!snapshot.hasData){
返回中心(
孩子:_showProgressBar,
);
}
List reversedDocuments=snapshot.data.documents.reversed.toList();
返回ListView.builder(
itemCount:reversedDocuments.length,
itemBuilder:(构建上下文,int索引){
字符串postAuthorID=reversedDocuments[index]。数据[“postAuthorID”]。toString();
字符串postAuthorName='';
Firestore.instance.collection(“用户”)
.where(“userID”,isEqualTo:postAuthorID).snapshots().listen((dataSnapshot){
打印(postAuthorName=dataSnapshot.documents[0]。数据[“用户名]);
设置状态(){
postAuthorName=dataSnapshot.documents[0]。数据[“用户名”];
});
});
String desc=reversedDocuments[index]。数据[“post_desc”]。toString();
返回新的ListTile(
标题:集装箱(
孩子:排(
儿童:[
扩大(
孩子:卡片(
子:新列(
儿童:[
列表砖(
title:Text(postAuthorName,//此处,值未更改,它保留空白。
样式:TextStyle(
字体大小:20.0,
),
),
字幕:文本(描述),
),
)
了解ListView.builder()只能基于DocumentSnapshot列表呈现项,并且不能处理生成器内部的查询
经过多次研究:
我尝试了许多替代方法,例如,尝试在initState()中构建列表,尝试使用嵌套流生成器:
return StreamBuilder<QuerySnapshot>(
stream: Firestore.instance.collection('posts').snapshots(),
builder: (context, snapshot1){
return StreamBuilder<QuerySnapshot>(
stream: Firestore.instance.collection("users").snapshots(),
builder: (context, snapshot2){
return ListView.builder(
itemCount: snapshot1.data.documents.length,
itemBuilder: (context, index){
String desc = snapshot1.data.documents[index].data['post_description'].toString();
String taskAuthorID = snapshot1.data.documents[index].data['post_authorID'].toString();
var usersMap = snapshot2.data.documents.asMap();
String authorName;
username.forEach((len, snap){
print("Position: $len, Data: ${snap.data["username"]}");
if(snap.documentID == post_AuthorID){
authorName = snap.data["username"].toString();
}
});
return ListTile(
title: Text(desc),
subtitle: Text(authorName), //Crashes here...
);
},
);
}
);
}
);
返回StreamBuilder(
流:Firestore.instance.collection('posts').snapshots(),
生成器:(上下文,快照1){
返回流生成器(
流:Firestore.instance.collection(“用户”).snapshots(),
生成器:(上下文,快照2){
返回ListView.builder(
itemCount:snapshot1.data.documents.length,
itemBuilder:(上下文,索引){
String desc=snapshot1.data.documents[index].data['post_description'].toString();
字符串taskAuthorID=snapshot1.data.documents[index].data['post_authorID'].toString();
var usersMap=snapshot2.data.documents.asMap();
字符串authorName;
username.forEach((len,snap){
打印(“位置:$len,数据:${snap.Data[“username”]}”);
if(snap.documentID==后期创作){
authorName=snap.data[“username”].toString();
}
});
返回列表块(
标题:文本(描述),
字幕:Text(authorName),//此处崩溃。。。
);
},
);
}
);
}
);
尝试使用Stream Group,但找不到完成此操作的方法,因为它只合并了两个流,但我希望第二个流由第一个流的值获取
这是我的Firebase系列屏幕截图:
Firestore“帖子”收藏:
Firestore“用户”集合:
我知道这是一件非常简单的事情,但仍然找不到任何教程或文章来实现这一点。我发布了一个类似的问题,后来找到了一个解决方案:使itemBuilder返回的小部件有状态,并在其中使用FutureBuilder 这是我的代码。在您的情况下,您可能希望使用新的有状态小部件而不是ListTile,这样您就可以添加FutureBuilder来调用异步函数
StreamBuilder(
stream: Firestore.instance
.collection("messages").snapshots(),
builder: (context, snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.none:
case ConnectionState.waiting:
return Center(
child: PlatformProgressIndicator(),
);
default:
return ListView.builder(
reverse: true,
itemCount: snapshot.data.documents.length,
itemBuilder: (context, index) {
List rev = snapshot.data.documents.reversed.toList();
ChatMessageModel message = ChatMessageModel.fromSnapshot(rev[index]);
return ChatMessage(message);
},
);
}
},
)
class ChatMessage extends StatefulWidget {
final ChatMessageModel _message;
ChatMessage(this._message);
@override
_ChatMessageState createState() => _ChatMessageState(_message);
}
class _ChatMessageState extends State<ChatMessage> {
final ChatMessageModel _message;
_ChatMessageState(this._message);
Future<ChatMessageModel> _load() async {
await _message.loadUser();
return _message;
}
@override
Widget build(BuildContext context) {
return Container(
margin: const EdgeInsets.symmetric(horizontal: 10.0, vertical: 10.0),
child: FutureBuilder(
future: _load(),
builder: (context, AsyncSnapshot<ChatMessageModel>message) {
if (!message.hasData)
return Container();
return Row(
children: <Widget>[
Container(
margin: const EdgeInsets.only(right: 16.0),
child: GestureDetector(
child: CircleAvatar(
backgroundImage: NetworkImage(message.data.user.pictureUrl),
),
onTap: () {
Navigator.of(context)
.push(MaterialPageRoute(builder: (context) =>
ProfileScreen(message.data.user)));
},
),
),
Expanded(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
message.data.user.name,
style: Theme.of(context).textTheme.subhead,
),
Container(
margin: const EdgeInsets.only(top: 5.0),
child: _message.mediaUrl != null
? Image.network(_message.mediaUrl, width: 250.0)
: Text(_message.text))
],
),
)
],
);
},
),
);
}
}
class ChatMessageModel {
String id;
String userId;
String text;
String mediaUrl;
int createdAt;
String replyId;
UserModel user;
ChatMessageModel({String text, String mediaUrl, String userId}) {
this.text = text;
this.mediaUrl = mediaUrl;
this.userId = userId;
}
ChatMessageModel.fromSnapshot(DocumentSnapshot snapshot) {
this.id = snapshot.documentID;
this.text = snapshot.data["text"];
this.mediaUrl = snapshot.data["mediaUrl"];
this.createdAt = snapshot.data["createdAt"];
this.replyId = snapshot.data["replyId"];
this.userId = snapshot.data["userId"];
}
Map toMap() {
Map<String, dynamic> map = {
"text": this.text,
"mediaUrl": this.mediaUrl,
"userId": this.userId,
"createdAt": this.createdAt
};
return map;
}
Future<void> loadUser() async {
DocumentSnapshot ds = await Firestore.instance
.collection("users").document(this.userId).get();
if (ds != null)
this.user = UserModel.fromSnapshot(ds);
}
}
StreamBuilder(
流:Firestore.instance
.collection(“messages”).snapshots(),
生成器:(上下文,快照){
交换机(快照.连接状态){
案例连接状态。无:
案例连接状态。正在等待:
返回中心(
子项:PlatformProgressIndicator(),
);
违约:
返回ListView.builder(
相反:是的,
itemCount:snapshot.data.documents.length,
itemBuilder:(上下文,索引){
List rev=snapshot.data.documents.reversed.toList();
ChatMessageModel message=ChatMessageModel.fromSnapshot(修订版[索引]);
返回聊天室消息(message);
},
);
}
},
)
类ChatMessage扩展StatefulWidget{
最终ChatMessageModel\u消息;
ChatMessage(此.\u消息);
@凌驾
_ChatMessageState createState()=>\u ChatMessageState(\u message);
}
类ChatMessageState扩展了状态{
最终ChatMessageModel\u消息;
_ChatMessageState(此.\u消息);
Future\u load()异步{
wait_message.loadUser();
返回消息;
}
@凌驾
小部件构建(构建上下文){
返回容器(
边距:常量边集。对称(水平:10.0,垂直:10.0),
[
Group_A header card,
Group_A's User_1 card,
Group_A's User_2 card,
Group_B header card,
Group_B's User_1 card,
Group_B's User_2 card,
]
class GroupWithUsers {
final Group group;
final List<User> users;
GroupWithUsers(this.group, this.users);
}
Stream<List<GroupWithUsers>> stream = Firestore.instance
.collection(GROUP_COLLECTION_NAME)
.orderBy('createdAt', descending: true)
.snapshots()
.asyncMap((QuerySnapshot groupSnap) => groupsToPairs(groupSnap));
return StreamBuilder(
stream: stream,
builder: (BuildContext c, AsyncSnapshot<List<GroupWithUsers>> snapshot) {
// build whatever
});
Future<List<GroupWithUsers>> groupsToPairs(QuerySnapshot groupSnap) {
return Future.wait(groupSnap.documents.map((DocumentSnapshot groupDoc) async {
return await groupToPair(groupDoc);
}).toList());
}
Future<GroupWithUsers> groupToPair(DocumentSnapshot groupDoc) {
return Firestore.instance
.collection(USER_COLLECTION_NAME)
.where('groupId', isEqualTo: groupDoc.documentID)
.orderBy('createdAt', descending: false)
.getDocuments()
.then((usersSnap) {
List<User> users = [];
for (var doc in usersSnap.documents) {
users.add(User.from(doc));
}
return GroupWithUser(Group.from(groupDoc), users);
});
}