Pagination with streams in flutter

Question

I have implemented a pagination scheme in my flutter app but im not sure if its performance friendly and if it may result to trouble on production in future so i would like to get advice on it. here is my implementation

First, i get data using a stream provider in my parent widget.

class BuyerSellerPostsPage extends StatefulWidget {

  @override
  _BuyerSellerPostsPageState createState() => _BuyerSellerPostsPageState();
}

class _BuyerSellerPostsPageState extends State<BuyerSellerPostsPage> {

   ...some code here...

   bool isAtBottom = false;
   int postToDisplay=10;

   @override
   void initState() {
     super.initState();
     // Setup the listener.
     _scrollController.addListener(() {
       if (_scrollController.position.atEdge) {
         if (_scrollController.position.pixels == _scrollController.position.maxScrollExtent) {
          setState(() {
            isAtBottom=true;
            postToDisplay+=10;
            print('now true');
          });
         }else{
           setState(() {
             print('now false');
            isAtBottom=false;
           });
         }
       }
     });
   }
  @override
  void dispose(){
     _scrollController.dispose();
     super.dispose();
  }

...some code here..

  @override
  Widget build(BuildContext context) {

    Position coordinates=Provider.of<Position>(context);

...some code here...

        body: SingleChildScrollView(
          controller: _scrollController,
            child: StreamProvider<List<SellerPost>>.value(
              value: SellerDatabaseService(
                  currentLocation: new GeoPoint(coordinates.latitude, coordinates.longitude,)
                  ,filters: _setFilters,
                  selectedCategory: _selectedCategory,
                selectedTag: _selectedTag,
                postsToDisplay: postToDisplay
              ).inRangeSellerPosts ,

                  ...some code here...

                                  );
                                }else{
                                  return Container(
                                  );
                                }
                              },
                            ),
                          ),
                          //post list
                          BSellerPostList(),

                       ...some code here...



  }
}

The initial posts to display are 10. In my initstate i have used a listener to my scroll controller so that when the user scrolls to the bottom more items(+10) are loaded on screen.

In my stream provider i pass the postsToDisplay int to my stream in the backend below

  Stream <List<SellerPost>> get inRangeSellerPosts {

    try {
      return sellerPostCollection
          .where("expireTime" , isGreaterThan: DateTime.now())
          .orderBy('expireTime',descending: true)
          .snapshots()
          .map(yieldSellerPosts);
    } catch (e) {
      print(e.toString());
      return null;
    }
  }
 
  List<SellerPost> yieldSellerPosts(QuerySnapshot snapshot) {
    List<String> l = [];
    print(snapshot.documents.length);
    try {
      return snapshot.documents.map((doc) {
        return SellerPost(
         ...some code here...
        );
      }).take(postsToDisplay)
          .toList();
    } catch (e) {
      print(e.toString());
      return null;
    }
  }

I now get the snapshots and use the take method on the list to get only the required number(postsToDisplay). This method works fine in my debug mode. Im not sure how it will behave in production or with large data sets. Could someone scrutinise it, i would appreciate alot.

question from:https://stackoverflow.com/questions/65641059/pagination-with-streams-in-flutter

Answer 1

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