Avoid ListView's unwanted refresh

Question

As the following animation displays, when I tap one of the list items that StreamBuilder() is querying, it shows the items data on the right darker container (it's always Instance of '_JsonQueryDocumentSnapshot'). But at the same time in each tap, the whole list is refreshing itself, which is not very cost-effective I believe.

How can I avoid this unwanted refresh? Answers with GetX state management dependency are also welcome.

class Schedule extends StatefulWidget {
  @override
  _ScheduleState createState() => _ScheduleState();
}

class _ScheduleState extends State<Schedule> {

  final FirebaseFirestore _db = FirebaseFirestore.instance;
  final DateTime _yesterday = DateTime.now().subtract(Duration(days: 1));

  var _chosenData;

  @override
  Widget build(BuildContext context) {
    return Row(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        Expanded(
          child: StreamBuilder<QuerySnapshot>(
            stream: _db.collection('Schedule').where('date', isGreaterThan: _yesterday).limit(10).orderBy('date').snapshots(),
            builder: (context, snapshot) {
              if (snapshot.connectionState == ConnectionState.active) {
                return ListView.builder(
                  itemCount: snapshot.data!.docs.length,
                  itemBuilder: (context, index) {
                    var data = snapshot.data!.docs[index];
                    return ListTile(
                      leading: Icon(Icons.person),
                      title: Text(data['project'], style: TextStyle(fontWeight: FontWeight.bold)),
                      subtitle: Text(data['parkour']),
                      onTap: () {
                        setState(() {_chosenData = data;});
                      },
                    );
                  },
                );
              } else {
                return Center(child: CupertinoActivityIndicator());
              }
            },
          ),
        ),
        VerticalDivider(),
        Expanded(
          child: Container(
            alignment: Alignment.center,
            color: Colors.black26,
            child: Text('$_chosenData'),
          ),
        ),
      ],
    );
  }
}

score 2 · Accepted Answer · edited Sep 04 '21 at 13:29

To me the easiest solution would be just make it stateless and use a Getx class.

class ScheduleController extends GetxController {
  var chosenData;

  void updateChosenData(var data) {
    chosenData = data;
    update();
  }
}

And your Schedule.dart would look like this:

class Schedule extends StatelessWidget {
  final FirebaseFirestore _db = FirebaseFirestore.instance;
  final DateTime _yesterday = DateTime.now().subtract(Duration(days: 1));

  @override
  Widget build(BuildContext context) {
    final controller = Get.put(ScheduleController());
    return Row(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        Expanded(
          child: StreamBuilder<QuerySnapshot>(
            stream: _db
                .collection('Schedule')
                .where('date', isGreaterThan: _yesterday)
                .limit(10)
                .orderBy('date')
                .snapshots(),
            builder: (context, snapshot) {
              if (snapshot.connectionState == ConnectionState.active) {
                return ListView.builder(
                  itemCount: snapshot.data!.docs.length,
                  itemBuilder: (context, index) {
                    var data = snapshot.data!.docs[index];
                    return ListTile(
                      leading: Icon(Icons.person),
                      title: Text(data['project'],
                          style: TextStyle(fontWeight: FontWeight.bold)),
                      subtitle: Text(data['parkour']),
                      onTap: () => controller.updateChosenData(data), // calls method from GetX class
                    );
                  },
                );
              } else {
                return Center(child: CupertinoActivityIndicator());
              }
            },
          ),
        ),
        VerticalDivider(),
        Expanded(
          child: Container(
            alignment: Alignment.center,
            color: Colors.black26,
            child: GetBuilder<ScheduleController>(
              builder: (controller) => Text('${controller.chosenData}'), // only this rebuilds
            ),
          ),
        ),
      ],
    );
  }
}

This way the listview.builder never rebuilds, only the Text widget directly inside the GetBuilder gets rebuilt when you selected a different ListTile.

score 0 · Answer 2 · answered Sep 03 '21 at 19:46

Calling setState() notifies the framework that the state of Schedule has changed, which causes a rebuild of the widget and so your StreamBuilder.

You could move your stream logic to an upper level of the widget tree. So, setState() will not trigger a rebuild of StreamBuilder.

class ParentWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StreamBuilder<QuerySnapshot>(
      stream: FirebaseFirestore.instance
          .collection('Schedule')
          .where(
            'date',
            isGreaterThan: DateTime.now().subtract(Duration(days: 1)),
          )
          .limit(10)
          .orderBy('date')
          .snapshots(),
      builder: (context, snapshot) {
        return Schedule(snapshot: snapshot); // Pass snapshot to Schedule
      },
    );
  }
}

Another approach would be using Stream.listen in initState() which is called once. This way your stream won't be subscribed for each time setState() is called.

...

late StreamSubscription<QuerySnapshot> _subscription;

@override
void initState() {
  _subscription = _db
    .collection('Schedule')
    .where('date', isGreaterThan: _yesterday)
    .limit(10)
    .orderBy('date')
    .snapshots()
    .listen((QuerySnapshot querySnapshot) {
      setState(() {
        _querySnapshot = querySnapshot;
      });
    });

  super.didChangeDependencies();
}

@override
void dispose() {
  _subscription.cancel(); // Cancel the subscription
  super.dispose();
}

...

Avoid ListView's unwanted refresh

2 Answers2