Flutter: Weird listview/stream builder behavior - flutter

I have a home_page.dart file whose body has a StreamBuilder it recieves the stream from my getChats() function. In the StreamBuilder's builder function I sort the all the documents after storing them in a list named docsList based on the lastMessageTime field so that the document with the latest message is at the top (first).
As the ListView is using the docsList for building the cards it is expected that the document which has the most resent message should be displayed first. Which only happens when the list is build for the first time. After that if I send a new message to the chat which is not at the top this happens:
Initially:
When I send a message which the text 'test' to the chat "Heah Roger" this is how the list gets updated:
As it can be seen the Time on the right and the subtext changes for the first tile but the image and name didn't (same for second tile). Even though the documents are updated in the docsList and are sorted in the desired manner (I printed it to check it). Somehow the photo and the name alone are not being updated in the UI alone.
Note: The correct fields are updated in the firestore. Also if I restart the app after killing it. It shows the desired result:
getChats()
Stream<QuerySnapshot<Map<String, dynamic>>> getChats(User currentUser) {
return FirebaseFirestore.instance
.collection('chats')
.where('users', arrayContains: currentUser.id)
.snapshots();
}
home_page.dart
body: StreamBuilder(
stream: RepositoryProvider.of<FirestoreRepository>(context).getChats(BlocProvider.of<AuthenticationBloc>(context).state.user),
builder: (context, AsyncSnapshot<dynamic> snapshot) {
if (snapshot.hasData && snapshot.data.docs.length > 0) {
List docsList = snapshot.data.docs;
docsList.sort((a, b) => b.data()['lastMessageTime'].compareTo(a.data()['lastMessageTime']));
return ListView.builder(
itemCount: docsList.length,
itemBuilder: (context, index) {
return SingleChatCard(chatRoom: ChatRoomModel.fromMap(docsList[index].data()));
},
);
} else {
return ...
}
},
),
Can anyone help me figure out the underlying problem that is causing this weird behavior?

Looks like an key issue to me,
When you're using your custom Widget to render in a listview, with some complicate data flow,
Flutter react to these changes one level at a time:
You can refer: https://www.youtube.com/watch?v=kn0EOS-ZiIc
In your example, you can do something like this:
return SingleChatCard(
key: ValueKey(index),
chatRoom: ChatRoomModel.fromMap(docsList[index].data()));
},

Related

Flutter, updating variable values not appearing in application

After defining a variable ("xyz" at screenshot), I fetched some data on my firestore database, then changed that variable value to data i fetched from firestore. When I print the changed variable with "print()" it appears at "Run" the value I fetched, which is what I want. But when I run the app, the text I assigned as changed variable appears on the screen with old value like I never changed it after defining. the code
When I print(xyz); it appears as the data from firestore, so there is no problem at database connection. I just want to update the value appears at screen too.
you could also listen to those snapshots without using StreamBuilder or any Flutter widget with the listen() method like this:
final fieldValue = "initial value";
FirebaseFirestore.instance
.doc(documentPath)
.snapshots()
.listen((snapshot) {
final data = snapshot.data() as Map<String, dynamic>;
fieldValue = data["field"];
print(fieldValue);
});
the fieldValue will be updated now every time an update happens to the document, and it will print it automatically in the console with the print()
as I see in the screenshot, you're getting your document's data with a Future, and the Future is useful when you need to call data just once :
FirebaseFirestore.instance.doc(documentPath).get(); // Future
FutureBuilder<DocumentSnapshot>(
future: FirebaseFirestore.instance.doc(documentPath).get(),
builder: (context, AsyncSnapshot<DocumentSnapshot> snapshot) {
if (snapshot.hasData) {
return Text("${snapshot.data!.data()}");
}
return Text("something else");
},
);
This will get the snapshot only once, even if you updated the document data, nothing will update on the screen until you make manually a new request to get another snapshot.
well the Firebase SDK for Flutter provide also Stream of snapshots for DocumentSnapshot and CollectionSnapshot, which listen directly to it, so whenever you have an update on your target, that stream will be notified and provide a new snapshot for that new updated data, and you can use it like this:
FirebaseFirestore.instance.doc(documentPath).snapshots(), // Stream
StreamBuilder<DocumentSnapshot>(
stream: FirebaseFirestore.instance.doc(documentPath).snapshots(), // Stream
builder: (context, AsyncSnapshot<DocumentSnapshot> snapshot) {
if (snapshot.connectionState == ConnectionState.active) {
final currentData = snapshot.data!.data() as Map<String, dynamic>;
final fieldValue = currentData["fieldString"];
return Text("$fieldValue");
}
return Text("something else");
},
);
change fieldString with your field name to get its value.
Now every update you do to the DocumentSnapshot, the StreamBuilder will get that new snapshot from the Stream and update the UI based on it.
Hope this helps!

Get stream of results from Firebase Realtime Database inside nested array inside nested document in Flutter

I am currently developing a chatting page on my mobile application and was using Realtime Database to reduce costs. Not having much Realtime Database experience, I am running into issues developing a page for active chatrooms where each user has a document with their uid where there is an array of chats . How can I generate a list of the first names based on the items inside of the array of chats.
I realize it's best practice to show code you have tried, however, I have only used Firebase Firestore and have no idea where to start, considering the complexity of the structure
You can try this answer.
Here I have created StreamBuilder for getting data once. As I have provided, Stream outside of StreamBuilder means it will create a stream only once.
final _snap = FirebaseDatabase.instance
.ref()
.child(`users/${uid}`)
StreamBuilder<Event>(
stream: _snap.onValue,
builder: (BuildContext context, snapshot) {
if (snapshot.hasData) {
DataSnapshot snap = snapshot.data as DataSnapshot;
List<dynamic> chatArray = snap.value['chats'];
List<String> firstNames = [];
for (var chat in chatArray) {
String firstName = chat[recepientFirstName];
firstNames.add(firstName);
}
return ListView.builder(
itemCount: firstNames.length,
itemBuilder: (context, index) {
return Text(firstNames[index]);
},
);
} else {
return Text('Loading...');
}
},
)
Found similar reference about this Questions so you can also visit these threads:
Thread1
Thread2
Thread3

Need I do pagination for flutter StreamBuilder?

I'm new to flutter, and now I'm creating an app which has a feed page, I'm using StreamBuilder + firestore to do this, the code is like this:
return StreamBuilder(
stream: FirebaseFirestore.instance
.collection('posts')
.orderBy('createdAt', descending: true)
.snapshots(),
builder: (context,
AsyncSnapshot<QuerySnapshot<Map<String, dynamic>>> snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return const Center(
child: CircularProgressIndicator(
color: primaryColor,
),
);
}
return ListView.builder(
itemCount: snapshot.data!.docs.length,
itemBuilder: (context, index) => Container(
child: createPostViewFromSnapShot(snapshot.data!.docs[index]),// it returns a widget
),
);
},
);
You can see from the code I didn't do pagination, I want to know when the code runs, it fetch all the post from firestore ? Or it will fetch data by block or something like pagination ?
I want to know if it's necessary to do pagination for StreamBuilder?
Avoid creating Widgets in Methods. That way you cause your App to
become I'm-performant. Because the Widget is not sat directly in the
Tree, but a method, every build that methods gets called, no matter
if the resulting widget would have to be actually be rebuilt.
That stream will not always emit events where data is not null. You will most likely get an exception for using snapshot.data! bang operator
Take a closer look at the documentation: https://firebase.flutter.dev/docs/firestore/usage/
FlutterFire provides support for dealing with realtime changes to
collections and documents. A new event is provided on the initial
request, and any subsequent changes to collection/document whenever a
change occurs (modification, deleted or added).
For what you are trying to achieve, it would be better to initially fetch a limited set of documents from your collection.
collectionReference.limit(42).get()
You can than fetch the next elements by using https://firebase.flutter.dev/docs/firestore/usage/#start--end-cursors

Flutter + Firestore chat .. Listview rebuilds all items

I'm trying to add chat functionality to my app (kind of similar to WhatsApp functionalities), using flutter and Firestore. The main structure on Firestore is to have 2 collections (I want the unread message count as well):
users: and each user will have a subcollection "chats" that will include all CHATS_IDs. This will be the main place to build home chat page (shows a history list of all chats) by getting the user chat list.
chats: a list of all chats and each chat document has a subcollection of messages.
My main issue is in building the home page (where a list of all user previous chats should appear). I get/subscribe the user chat subcollection, and for each chat ID listed in there I also subscribe for the chat itself in the chat collection (using the ID).
Here are screenshots of it in principle:
users collection:
chats coleection:
and here is the main screen of interest (principle from whatsapp screen):
What I'm doing is that I retrieve user's chat subcollection (and register a listener to it using StreamBuilder), and also for number of unread messages/last message and last message time, I subscribe to listen for each of these chats (and want to use each user last message time, status and his last presence in that chat doc to calculate the unread count) .
The problem is that Listview.builder rebuilds all items (initially and on scroll) instead of just the viewed ones. here is my code:
Stream<QuerySnapshot> getCurrentUserChats(userId) {
return FirebaseFirestore.instance
.collection(AppConstants.USERS_COLLECTION)
.doc('$userId')
.collection(AppConstants.USER_CHATS_SUBCOLLECTION)
.orderBy('lastMsgTS', descending: true)
.snapshots()
.distinct();
}
Widget getRecentChats(userId) {
return StreamBuilder<QuerySnapshot>(
stream: getCurrentUserChats(userId),
builder: (context, snapshot) {
if (snapshot.hasData && snapshot.data.docs.isNotEmpty) {
print('snapshot of user chats subcoll has changed');
List<QueryDocumentSnapshot> retrievedDocs = snapshot.data.docs;
return Container(
height: 400,
child: ListView.builder(
//childrenDelegate: SliverChildBuilderDelegate(
itemCount: snapshot.data.size,
itemBuilder: (context, index) {
String chatId = retrievedDocs[index].id;
print('building index: $index, chatId: $chatId');
return StreamBuilder(
stream: FirebaseFirestore.instance
.collection(AppConstants.CHATS_COLLECTION)
.doc('$chatId')
.snapshots()
.distinct(),
builder:
(context, AsyncSnapshot<DocumentSnapshot> snapshot) {
if (snapshot.hasData) {
print('${snapshot.data?.id}, isExist: ${snapshot.data?.exists}');
if (snapshot.data.exists) {
return KeyProxy(
key: ValueKey(chatId),
child: ListTile(
leading: CircleAvatar(
child: Container(
//to be replaced with user image
color: Colors.red,
),
),
title: Text('$chatId'),
subtitle: Text(
"Last Message received on: ${DateTimeUtils.getDateViewFromDT(snapshot.data.data()['ts']?.toDate())}"),
),
);
}
}
return SizedBox.shrink();
},
);
},
/*childCount: snapshot.data.size,
findChildIndexCallback: (Key key) {
print('calling findChildIndexCallback');
final ValueKey valKey = key;
final String docId = valKey.value;
int idx = retrievedDocs.indexOf(retrievedDocs
.where((element) => element.id == docId)
.toList()[0]);
print('docId: $docId, idx: $idx');
return idx;
}*/
),
);
}
return Center(child: UIWidgetUtils.loader());
});
}
After searching, I found these related suggestions (but both didn't work):
A github issue suggested thesince the stream is reordarable (github: [https://github.com/flutter/flutter/issues/58917]), but even with using ListView.custom with a delegate and a findChildIndexCallback, the same problem remained.
to use distinct.
But removing the inner streambuilder and just returning the tiles without a subscription, makes the ListView.builder work as expected (only builds the viewed ones). So my questions are:
Why having nested stream builders causing all items to be rebuil.
is there a better structure to implement the above features (all chats with unread count and last message/time in real-time). Especially that I haven't added lazy loading yet. And also with this design, I have to update multiple documents for each message (in chats collection, and each user's subcollection).
Your help will be much appreciated (I have checked some other SO threads and medium articles, but couldn't find one that combines these features in one place with and preferably with optimized design for scalability/price using Firestore and Flutter).
I think that You can do this:
Widget build(ctx) {
return ListView.builder(
itemCount: snapshot.data.size,
itemBuilder: (index, ctx) =>_catche[index],
)
}
and for _catche:
List<Widget> _catche = [/*...*/];
// initialize on load

Function invoke in Flutter to get attributes from Firebase

I want to define and invoke a function in Flutter to get required values from Firebase.
In the below code I have defined getCourseDetails() function and invoking it in the container by passing a parameter to get the value.
The Course_Details collection has many documents with course_id's which has attribute with name (course_name, subtitle). I use these values to build a listview cards in next steps.
I am able to get the values from the function using async await, but for some reason the values keeps on updating and never stops. It kind of goes to loop and keeps on running. I added print statements to check and it keeps on running and printing.
Please let me know what wrong I am doing here or how to define function here to avoid the issue. Thanks
class _CourseProgressListState extends State<CourseProgressList> {
String course_name, subtitle;
getCourseDetails(course_id_pass) async {
DocumentSnapshot document = await Firestore.instance.collection('Course_Details').document(course_id_pass).get();
setState(() {
course_name = document.data['course_name'];
subtitle = document.data['subtitle'];
});
}
#override
Widget build(BuildContext context) {
return Container(
child: StreamBuilder(
stream: Firestore.instance.collection('Enrolling_Courses').where('student_id', isEqualTo: widget.id).snapshots(),
builder: (context, snapshot) {
if (snapshot.data == null) return Text('no data');
return ListView.builder(
itemCount: snapshot.data.documents.length,
itemBuilder: (_, int index) {
var course_details = snapshot.data.documents[index];
getCourseDetails(course_details['course_id']);
Application Flow
On first build of CourseProgressList the Widget State _CourseProgressListState is loaded. This State in the build method uses a StreamBuilder to retrieve all documents from the firestore. As soon as the documents are received the StreamBuilder attempts to build the ListView using the ListViewBuilder.
In the ListViewBuilder you make the async call to getCourseDetails(course_details['course_id']); which when complete populates two attributes String course_name, subtitle;
The problem starts here
Problem
When you call
setState(() {
course_name = document.data['course_name'];
subtitle = document.data['subtitle'];
});
you trigger a Widget rebuild and so the process starts over again to rebuild the entire widget.
NB. refreshing state of a stateful widget will trigger a widget rebuild
NB. Firestore.instance.collection('Enrolling_Courses').where('student_id', isEqualTo: widget.id).snapshots() returns a stream of realtime changes implying that your List will also refresh each time there is a change to this collection
Recommendations
If you do not need to call the setState try not to call the setState.
You could let getCourseDetails(course_id_pass) return a Future/Stream with the values desired and use another FutureBuilder/StreamBuilder in your ListViewBuilder to return each ListViewItem. Your user may appreciate seeing some items instead of waiting for all the course details to be available
Abstract your request to firestore in a repository/provider or another function/class which will do the entire workload, i.e retrieving course ids then subsequently the course details and returning a Future<List<Course>> / Stream<List<Course>> for your main StreamBuilder in this widget (see reference snippet below as a guide and requires testing)
Reference Snippet
Your abstraction could look something like this but this decision is up to you. There are many software design patterns to consider or you could just start by getting it working.
//let's say we had a class Course
class Course {
String courseId;
String courseName;
String subTitle;
Course({this.courseId,this.courseName,this.subTitle})
}
Stream<List<Course>> getStudentCourses(int studentId){
return Firestore.instance
.collection('Enrolling_Courses')
.where('student_id', isEqualTo: studentId)
.snapshots()
//extract documents from snapshot
.map(snapshot => snapshot?.data ?? [])
//we will then request details for each document
.map(documents =>
/*because this is an asynchronous request for several
items which we are all interested in at the same time, we can wrap
this in
a Future.wait and retrieve the results of all as a list
*/
Future.wait(
documents.map(document =>
//making a request to firestore for each document
Firestore.instance
.collection('Course_Details')
.document(document['course_id'])
.get()
/* making a final transformation turning
each document into a Course item which we can easily pass to our
ListBuilder/Widgets
*/
.then(courseItem => Course(
courseId:document['course_id'],
courseName:
courseItem.data['course_name'],
subTitle:
courseItem.data['subtitle']
)
)
)
)
);
}
References/Resources
FutureBuilder - https://api.flutter.dev/flutter/widgets/FutureBuilder-class.html
StreamBuilder - https://api.flutter.dev/flutter/widgets/StreamBuilder-class.html
Future.wait - https://api.flutter.dev/flutter/dart-async/Future/wait.html