Why this future function is returning empty list flutter

Question

I am new with flutter having issues with the future functions. I had a single await function on other screen and its returning list but when I use multiple await function in a single future function it returns an empty list and executes before many other await functions to execute. My Question is why my future functions are returning an empty list I had tried almost everything on the internet please help

  Future<List<AllShefz>> getAllShefz() async {
    List<AllShefz> allShefz = [];
    var data = await FirebaseDatabase.instance
        .reference()
        .child("Resturants")
        .once()
        .then((DataSnapshot datasnapshot) async {
      if (datasnapshot != null) {
        Map<dynamic, dynamic> values = await datasnapshot.value;
        values.forEach((key, value) async {
          await FirebaseDatabase.instance
              .reference()
              .child("Resturants")
              .child(key)
              .child("Profile")
              .once()
              .then((DataSnapshot snapshot) async {
            print(" I am here");
            Map<dynamic, dynamic> newvals = await snapshot.value;
            var position, name, gender, status;
            if (await snapshot.value != null) {
              position = await newvals["Position"];
              name = await newvals["Name"];
              gender = await newvals["Gender"];
              status = await newvals["Status"];
              if (position != null && status == "Approaved") {
                var arr = ltlnClass().getSplit(position);
                String latStr = arr[0];
                String lngStr = arr[1];
                String myPosition;
                await new MyLocation()
                    .getMyLocation()
                    .then((value) => {myPosition = value.toString()});
                var arr2 = ltlnClass().getSplit(myPosition);
                String latStr2 = arr2[0];
                String lngStr2 = arr2[1];
                double lat2 = double.parse(
                    ltlnClass().getLtlng(ltlnClass().getIndex(latStr), latStr));
                double lng2 = double.parse(
                    ltlnClass().getLtlng(ltlnClass().getIndex(lngStr), lngStr));
                double lat1 = double.parse(ltlnClass()
                    .getLtlng(ltlnClass().getIndex(latStr2), latStr2));
                double lng1 = double.parse(ltlnClass()
                    .getLtlng(ltlnClass().getIndex(lngStr2), lngStr2));
                double distance =
                    DistanceCalculator().distance(lat1, lat2, lng1, lng2);
                print("Lng 1" + lng1.toString());
                print("Lng 2" + lng2.toString());
                print("Lat 1" + lat1.toString());
                print("Lat 2" + lat2.toString());
                print("Distance is " + distance.toString());
                AllShefz myShef =
                    new AllShefz(key, position, distance, gender, name, status);
                setState(() {
                  allShefz.add(myShef);
                });
              }
            }
            return allShefz;
          });
        });
      } else {
        print("Null value found");
      }
    });

    return allShefz;
  }

```.

Answer 1

You seem to be mixing .then and await calls. That is possible, but extremely error-prone for beginners (and frankly even experts if they did not have the correct dose of caffeine yet).

I suggest you remove all .then continuations and replace them with await. That way you can properly debug your code and find out where you missed out on waiting for a async call. Your indentation level should shrink to something manageable and you will be able to find the mistake easily.

Answer 2

As @nvoigt mentioned, you should change your code. Now you can easily debug your result step by step.

 Future<List<AllShefz>> getAllShefz() async {
    List<AllShefz> allShefz = [];
    var datasnapshot =
        await FirebaseDatabase.instance.reference().child("Resturants").once();

    if (datasnapshot != null) {
      Map<dynamic, dynamic> values = await datasnapshot.value;
      values.forEach((key, value) async {
        var snapshot = await FirebaseDatabase.instance
            .reference()
            .child("Resturants")
            .child(key)
            .child("Profile")
            .once();

        print(" I am here");
        Map<dynamic, dynamic> newvals = await snapshot.value;
        var position, name, gender, status;
        if (await snapshot.value != null) {
          position = await newvals["Position"];
          name = await newvals["Name"];
          gender = await newvals["Gender"];
          status = await newvals["Status"];
          if (position != null && status == "Approaved") {
            var arr = ltlnClass().getSplit(position);
            String latStr = arr[0];
            String lngStr = arr[1];
            String myPosition;
            var value = await new MyLocation().getMyLocation();

            myPosition = value.toString();

            var arr2 = ltlnClass().getSplit(myPosition);
            String latStr2 = arr2[0];
            String lngStr2 = arr2[1];
            double lat2 = double.parse(
                ltlnClass().getLtlng(ltlnClass().getIndex(latStr), latStr));
            double lng2 = double.parse(
                ltlnClass().getLtlng(ltlnClass().getIndex(lngStr), lngStr));
            double lat1 = double.parse(
                ltlnClass().getLtlng(ltlnClass().getIndex(latStr2), latStr2));
            double lng1 = double.parse(
                ltlnClass().getLtlng(ltlnClass().getIndex(lngStr2), lngStr2));
            double distance =
                DistanceCalculator().distance(lat1, lat2, lng1, lng2);
            print("Lng 1" + lng1.toString());
            print("Lng 2" + lng2.toString());
            print("Lat 1" + lat1.toString());
            print("Lat 2" + lat2.toString());
            print("Distance is " + distance.toString());
            AllShefz myShef =
                new AllShefz(key, position, distance, gender, name, status);
            setState(() {
              allShefz.add(myShef);
            });
          }
        }
        return allShefz;
      });
    } else {
      print("Null value found");
    }

    return allShefz;
  }