Flutter Firestore Convert Stream To Future - flutter

Question

I have a firestore stream in flutter that I would instead like to be a future so that I can do pagination of requests. Currently I periodically increase the limit variable in the code below and reload the whole original stream plus new data. This is very irritating because every time the limit variable increases the widget (a listview) scrolls to the top. I would like to ask how to convert the stream below into a future and how to place its contents into a list. My purpose of doing so being that the contents of all the future calls will be accumulated in an list and my listview will be generated off of that array, hopefully without scrolling to the top every time.
My other reason for doing so is to save memory on the client device. When a user scrolls down I would like to remove items from the front of the list to save memory and reload them only if the user scrolls back up. My project is a social-media application so I foresee users scrolling down indefinitely and using up all their phone memory. I am new to flutter so I would also like to ask if this memory usage is a valid concern.
Stream<List<Memo>> getFeed(int limit) async* {
yield* Firestore.instance
.collection('memos')
.where('followers', arrayContains: userid)
.orderBy("date")
.limit(limit) // TODO: add pagination of request
// .startAfterDocument(null)
.snapshots()
.map(_snapshotToMemoList);
}
My Streamsubscription and listview builder code is as follows:
Widget build(BuildContext context) {
return StreamBuilder<List<Memo>>(
stream: dbService( user: widget.user ).getFeed( streamLimit ),
builder: (BuildContext context, AsyncSnapshot<List<Memo>> snapshot) {
if (snapshot.hasError) return Text('Error: ${snapshot.error}');
switch (snapshot.connectionState) {
case ConnectionState.waiting:
return Text('Loading...');
default:
if (snapshot.data.isEmpty) {
return Text('EMPTY');
}
// streamSub.cancel();
// return Text(snapshot.data[1].body);
return ListView.builder(
controller: _scrollController,
itemCount: snapshot.data.length,
itemBuilder: (BuildContext context, int index) {
return Container(
height: 600,
child: Text(snapshot.data[index].body)
);
}
);
}
},
);
Lastly, my limit increasing function is
void initState() {
if (lastScrollPosition != null) _scrollController.jumpTo(lastScrollPosition);
_scrollController.addListener(() {
final maxScroll = _scrollController.position.maxScrollExtent;
// print(maxScroll);
final currentScroll = _scrollController.position.pixels;
// print(currentScroll);
if (maxScroll - currentScroll <= _scrollThreshold) {
setState(() {
lastScrollPosition = currentScroll;
streamLimit += 1;
print('increasing');
});
}
});
}