How to use querySnapshot in a listview builder? (flutter) - flutter

Question

I'm trying to fetch documents from my firebase DB and use them to create a social media feed. Here I'm trying to get the length of the fetched collection but I cannot manage to call the variable. Any help would be appreciated. Example code
class LoadDataFromFirestore extends StatefulWidget {
#override
_LoadDataFromFirestoreState createState() => _LoadDataFromFirestoreState();
}
class _LoadDataFromFirestoreState extends State<LoadDataFromFirestore> {
#override
void initState() {
super.initState();
CollectionReference _collectionRef =
FirebaseFirestore.instance.collection('fish');
Future<void> getData() async {
// Get docs from collection reference
QuerySnapshot querySnapshot = await _collectionRef.get();
// Get data from docs and convert map to List
final allData = querySnapshot.docs.map((doc) => doc.data()).toList();
print(allData);
}
}
Widget build(BuildContext context) {
return Scaffold(
body: ListView.builder(
itemCount: querySnapshot.docs.length,
itemBuilder: (BuildContext context, int index) {
return _postView();
},
),
);
}
}

Answer 1

First of all it is not ok to call future function in initstate, you need to use FutureBuilder like this:
class LoadDataFromFirestore extends StatefulWidget {
#override
_LoadDataFromFirestoreState createState() => _LoadDataFromFirestoreState();
}
class _LoadDataFromFirestoreState extends State<LoadDataFromFirestore> {
late CollectionReference _collectionRef;
#override
void initState() {
super.initState();
_collectionRef = FirebaseFirestore.instance.collection('fish');
}
Widget build(BuildContext context) {
return Scaffold(
body: FutureBuilder<QuerySnapshot>(
future: _collectionRef.get(),
builder: (context, snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.waiting:
return Text('Loading....');
default:
if (snapshot.hasError) {
return Text('Error: ${snapshot.error}');
} else {
QuerySnapshot? querySnapshot = snapshot.data;
return ListView.builder(
itemCount: querySnapshot?.docs?.length ?? 0,
itemBuilder: (BuildContext context, int index) {
var data = querySnapshot?.docs?[index].data();
print("data = $data");
return _postView();
},
);
}
}
},
),
);
}
}
inside listview's builder you can use data to parse your data and use it.

Answer 2

You can use FutureBuilder like this:
class LoadDataFromFirestore extends StatefulWidget {
const LoadDataFromFirestore({super.key});
#override
State<LoadDataFromFirestore> createState() => _LoadDataFromFirestoreState();
}
class _LoadDataFromFirestoreState extends State<LoadDataFromFirestore> {
//TODO change Map<String, dynamic> with your data type with fromJson for example
Future<List<Map<String, dynamic>>> _getData() async {
final querySnapshot = await FirebaseFirestore.instance.collection('fish').get();
return querySnapshot.docs.map((doc) => doc.data()).toList();
}
Widget build(BuildContext context) {
return Scaffold(
body: FutureBuilder<List<Map<String, dynamic>>>(
future: _getData(),
builder: (context, snapshot) {
if (snapshot.hasData) {
return ListView.builder(
itemCount: snapshot.data!.length,
itemBuilder: (context, index) {
return _postView(/* Ithink you have to pass here your item like snapshot.data[index]*/);
},
);
} else {
return const Center(child: CircularProgressIndicator());
}
},
),
);
}
}