Is there anyway to sort incoming data from StreamBuilder? - firebase

Question

Stream<QuerySnapshot> _usersStream = FirebaseFirestore.instance.collection('Listings').snapshots();
I am using this stream.
And i have streambuilder like this.
Flexible(
child: StreamBuilder<QuerySnapshot>(
stream: _usersStream,
builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
if (snapshot.hasError) {
return Text('Error');
}
if (snapshot.connectionState == ConnectionState.waiting) {
return Text("Loading");
}
return ListView(
children: snapshot.data!.docs.map((DocumentSnapshot document) {
Map<String, dynamic> data = document.data()! as Map<String, dynamic>;
String start_location=data['start_location'];
String end_location=data['end_location'];
String date=data['date'];
String time=data['time'];
String price=data['price'];
String name_surname=data['name_surname'];
String userId=data['user_id'];
String coord=data['coord'];
var splitted=coord.split('/');
for(int i=0; i<splitted.length-1; i++){
String x = splitted[i];
var splitted2=x.split('-');
double result=calculateDistance(widget.place_latlng.latitude, widget.place_latlng.longitude, double.parse(splitted2[0]), double.parse(splitted2[1]));
if(result<1 && start_location!= widget.placename){
print("Found!");
return GestureDetector(
onTap: (){
//onTap func
},
child: buildTripCard(
context,
start_location: start_location,
end_location: end_location,
date: date,
time: time,
price: price,
name_surname: name_surname,
userId: userId,
),
);
}
}
return Container();
}).toList(),
);
},
),
)
I put into the incoming data to calculateDistance function. It returns double value (result).If that value less than 1, it shows in ListView. What i want to do is, sort Data which shows in listView order by result value.
How can i reach list that i created with .toList() method?

Answer 1

Sort data by chaining into stream. The below example takes all photos, which title starts with p. Converting Future to Stream is just for demonstration.
Stream<List<Photo>> photos() {
return Stream.fromFuture(
http.get(Uri.parse('https://jsonplaceholder.typicode.com/photos'))
).map((r) => parsePhotos(r.body))
.map((list) => list.where((p) => p.title.startsWith('p')).toList());
}
Then use ListView.builder to render the final list.
StreamBuilder<List<Photo>>(
stream: photos(),
builder: (context, snapshot) {
if (snapshot.hasError) {
return const Center(
child: Text('An error has occurred!'),
);
} else if (snapshot.hasData) {
final photos = snapshot.data!;
return ListView.builder(
itemCount: photos.length,
itemBuilder: (context, index) {
return Text(photos[index].title);
},
);
} else {
return const Center(
child: CircularProgressIndicator(),
);
}
}