Question

我正在使用此应用程序，需要从API获取信息。我需要接收数据以在用户向下滚动时显示它。问题在于Stream Builder快照不接收任何数据。我有这个课程：

页面

class BotonesPage extends StatelessWidget {
  BotonesPage({Key key}) : super(key: key);

  final caracteresProvider = new Provider();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children: <Widget>[
          _fondoApp(),
          SingleChildScrollView(
            child: Column(
              children: <Widget>[
                _titulos(),
                StreamBuilder(
                  stream: caracteresProvider.popularesStream,
                  builder: (BuildContext context, AsyncSnapshot<List> snapshot) {

                    if ( snapshot.hasData ) {
                      return CharactersVertical(
                        caracter: snapshot.data,
                        siguientePagina: caracteresProvider.getCaracteres,
                      );
                    } else {
                      return Center(child: CircularProgressIndicator());
                    }
                  },
                ),
              ],
            ),
          )
        ],
      ),
    );
  }

我从API获取信息的提供者。

class Provider {

  final String _baseUrl = 'rickandmortyapi.com';
  final String _charactersPath = '/api/character/';

  bool _cargando     = false;

  List<Caracter> _populares = new List();

  final _popularesStreamController = StreamController<List<Caracter>>.broadcast();

  Function(List<Caracter>) get popularesSink => _popularesStreamController.sink.add;

  Stream<List<Caracter>> get popularesStream => _popularesStreamController.stream;

  void disposeStreams() {
    _popularesStreamController?.close();
  }

  Future<List<Caracter>> _procesarRespuesta(Uri url) async {

    log(url.toString());
    final resp = await http.get( url );
    final decodedData = json.decode(resp.body);

    final caracteres = new Caracteres.fromJsonList(decodedData['results']);

    return caracteres.items;
  }

  int _pages = 1;

  Future<List<Caracter>> getCaracteres() async {

    if ( _cargando ) return [];

    _cargando = true;

    final url = Uri.https(_baseUrl, _charactersPath, { 'page' : _pages.toString() });
    _pages++;
    final resp = await _procesarRespuesta(url);

    _populares.addAll(resp);
    popularesSink( _populares );

    _cargando = false;
    return resp;
  }

}

小部件

class CharactersVertical extends StatelessWidget {

  final List<Caracter> caracter;
  final Function siguientePagina;

  CharactersVertical({ @required this.caracter, @required this.siguientePagina });

  final _pageController = new PageController(
      initialPage: 1,
      viewportFraction: 0.3
  );

  @override
  Widget build(BuildContext context) {
    final _screenSize = MediaQuery.of(context).size;

    _pageController.addListener( () {

      if ( _pageController.position.pixels >= _pageController.position.maxScrollExtent - 200 ){
        siguientePagina();
      }
    });

    return Container(
      height: _screenSize.height * 0.2,
      child: PageView.builder(
        pageSnapping: false,
        controller: _pageController,
        itemCount: caracter.length,
        itemBuilder: ( context, i ) => _crearBotonRedondeado(context, caracter[i] ),
      ),
    );
  }

  ...
}

Stream Builder无法接收数据Flutter

0 个答案: