Sort dynamically ListView in Flutter

Question

I would like to sort a ListView based on a StreamController in a BottomNavigationBar. The problem is that the Listview doesn't refresh when I click the button on the app bar.

I would like to pass as parameter the function (Comparable of Company) which the user chooses.

Here's my code:

Home.dart

final CompanyService _companyService = CompanyService();
final AuthService _auth = AuthService();

class HomePage extends StatefulWidget {
  HomePage({Key key}) : super(key: key);
  Home createState() => Home();
}

class Home extends State<HomePage> {
  Comparator<Company> _sortFunction;
  int _currentIndex;
  var _tabs = [];

  @override
  void initState() {
    super.initState();
    _currentIndex = 0;

    _sortFunction = (a, b) => a.name.compareTo(b.name);
  }

  PreferredSize getDoubleHomeAppBar() {
    return PreferredSize(
        preferredSize: Size.fromHeight(55.0),
        child: Row(
          children: <Widget>[
            Expanded(
              child: Container(
                padding: EdgeInsets.only(left: 12.0),
                margin:
                    const EdgeInsets.only(left: 12.0, bottom: 8.0, right: 12.0),
                color: PRIMARY_COLOR,
              ),
            ),
            FlatButton.icon(
              icon: Icon(Icons.sort_by_alpha),
              label: Text(
                'Sort',
              ),
              onPressed: () {
                setState(() {
                  _sortFunction = (a, b) => b.city.compareTo(a.city);
                  _tabs[0] = CompanyTab(sortFunction: _sortFunction);
                });
              },
            ),
          ],
        ));
  }

  @override
  Widget build(BuildContext context) {

    _tabs = [
      CompanyTab(sortFunction: _sortFunction),
      MapTab(),
      Center(child: Text('Profile')),
      Center(child: Text('Settings')),
    ];

    return Scaffold(
      backgroundColor: BACKGROUND_COLOR,
      appBar: AppBar(
        elevation: 0.0,
        centerTitle: true,
        title: Text(
          'JobAdvisor',
          style: TextStyle(
            fontSize: MediaQuery.of(context).size.height / 24,
            fontWeight: FontWeight.bold,
            color: Colors.white,
          ),
        ),
        bottom: _currentIndex == 0 ? getDoubleHomeAppBar() : null,
        actions: <Widget>[...],
      ),
      body: _tabs[_currentIndex],
      bottomNavigationBar: BottomNavigationBar(
        currentIndex: _currentIndex,
        backgroundColor: BACKGROUND_COLOR,
        type: BottomNavigationBarType.fixed,
        items: [
          ...
        ],
        onTap: (index) {
          setState(() {
            _currentIndex = index;
            print('Index: $index');
            print('Current index: $_currentIndex');
          });
        },
      ),
    );
  }
}

CompanyTab.dart

@immutable
class CompanyTab extends StatefulWidget {
  final CompanyService _companyService = CompanyService();
  final Comparator<Company> sortFunction;

  CompanyTab({Key key, this.sortFunction}) : super(key: key);

  @override
  _CompanyTabState createState() =>
      _CompanyTabState(_companyService, sortFunction);
}

class _CompanyTabState extends State<CompanyTab> {
  StreamController<List<Company>> _streamController;
  final CompanyService _companyService;
  Comparator<Company> sortFunction;

  _CompanyTabState(this._companyService, this.sortFunction);

  @override
  void initState() {
    super.initState();
  }

  StreamBuilder companyList() {
    return StreamBuilder<List<Company>>(
        initialData: [],
        stream: _streamController.stream,
        builder: (BuildContext context, AsyncSnapshot<List<Company>> snapshot) {
          if (snapshot.hasError) {
            return Text("Something went wrong");
          }

          if (snapshot.connectionState == ConnectionState.waiting ||
              snapshot.connectionState == ConnectionState.none ||
              snapshot.data == null) {
            return LoadingWidget();
          } else {
            return ListView.builder(
                padding: const EdgeInsets.all(10),
                itemCount: snapshot.data.length,
                itemBuilder: (BuildContext context, int index) {
                  Company company = snapshot.data.elementAt(index);

                  ...
                }
          }
        });
  }

  @override
  void dispose() {
    _streamController.close();
    super.dispose();
  }

  void _getData() {
    _streamController = new StreamController<List<Company>>();
    _companyService.getCompanies().then((value) => {_elaborateList(value)});
  }

  void _elaborateList(List<Company> list) {
    List<Company> tmp = list;
    tmp.sort(sortFunction);
    print(tmp.toString());
    _streamController.sink.add(tmp);
  }

  @override
  Widget build(BuildContext context) {
    _getData();
    return Center(
      child: Container(
        child: companyList(),
      ),
    );
  }
}

Answer 1

I think the problem is in your sort method. It should be like this:

     _sortFunction.sort((a, b) => a.name.compareTo(b.name));

You can read from the official document.

EDIT:

And you need to use sortFunction of the widget in here:

     tmp.sort(widget.sortFunction);

You are not using the same sortFunction in CompanyTab. You should use the sortFunction which comes as a parameter. Here is a blog about it.