flutter - Flutter StatefulWidget中的变量范围

我尝试访问moviesList中的build()并得到如下结果。如果有人能指出真正的问题是。事先谢谢。

flutter: ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
flutter: The following NoSuchMethodError was thrown building MyListScreen(dirty, state:
flutter: _MyListScreenState#21007):
flutter: The getter 'results' was called on null.
flutter: Receiver: null
flutter: Tried calling: results

代码段如下：

class _MyListScreenState extends State<MyListScreen> {

  MoviesList moviesList;

  _getLatestMovies() {
    APIService.getMoviesNowPlaying().then((response) {
      setState(() {
        final jsonData = json.decode(response.body);
        moviesList = new MoviesList.fromJson(jsonData);
        // moviesList(new MoviesList.fromJson(jsonData));

        for (var i = 0; i < moviesList.results.length; i++) {
        print(moviesList.results[i].title);
        }
      });
    });
  }

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

  @override
  Widget build(context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("View Title"),
        ),
        body: ListView.separated(
          padding: EdgeInsets.zero,
          itemCount: moviesList.results.length,
          itemBuilder: (context, index) {
            // return ListTile(title: Text(moviesList.results[index].title));
          },
          separatorBuilder: (context, index) {
            return Divider();
          },
        ));
  }
}

最佳答案

使用

itemCount: moviesList != null ? moviesList.results.length : 0,

在初始化build()之前调用了您的moviesList，因此我们首先检查一下null，如果null使用0作为itemCount否则使用它的长度。

关于flutter - Flutter StatefulWidget中的变量范围，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/56795355/