dart - Flutter List View 构建 ListView 报错

Question

我在构建 ListView 时遇到错误，起初我以为 API 没有返回任何内容，但我在 flutter 中打印了 movies 变量，它控制台记录了这些值。顺便说一句，我正在尝试重新创建这个项目:

https://github.com/mlabouardy/flutter-watchnow

我得到的错误是:

RangeError (index): Invalid value: Valid value range is empty: 0

这是 ListView 生成器:

class TopMoviesState extends State<TopMovies> {
  List<Movie> _movies = new List();
  final _apiGatewayURL = "https://gfioehu47k.execute-api.us-west-1.amazonaws.com/staging/main";

  Widget _fetchMovies() {
    return new ListView.builder(
        padding: const EdgeInsets.all(16.0),
        itemBuilder: (context, i){
          return new Card(
              child: new Container(
                  height: 250.0,
                  child: new Padding(
                      padding: new EdgeInsets.all(2.0),
                      child: new Row(
                          children: <Widget>[
                            new Align(
                              child: new Hero(
                                  child: new Image.network("https://image.tmdb.org/t/p/w500"+this._movies[i].getPoster()),
                                  tag: this._movies[i].getTitle()
                              ),
                              alignment: Alignment.center,
                            ),
                            new Expanded(
                                child: new Stack(
                                    children: <Widget>[
                                      new Align(
                                        child: new Text(
                                          this._movies[i].getTitle(),
                                          style: new TextStyle(fontSize: 11.0, fontWeight: FontWeight.bold),
                                        ),
                                        alignment: Alignment.topCenter,
                                      ),
                                      new Align(
                                        child: new Padding(
                                            padding: new EdgeInsets.all(4.0),
                                            child: new Text(
                                                this._movies[i].getOverview(),
                                                maxLines: 8,
                                                overflow: TextOverflow.ellipsis,
                                                style: new TextStyle(fontSize: 12.0, fontStyle: FontStyle.italic)
                                            )
                                        ),
                                        alignment: Alignment.centerRight,
                                      ),
                                      new Align(
                                        child: new Text(
                                          this._movies[i].getReleaseDate(),
                                          style: new TextStyle(fontSize: 11.0, fontWeight: FontWeight.bold),
                                        ),
                                        alignment: Alignment.bottomRight,
                                      ),
                                    ]
                                )
                            )
                          ]
                      )
                  )
              )
          );
        }
    );
  }

这就是我运行从 API 获取的每个值的方式:

void _addMovie(dynamic movie){
this._movies.add(new Movie(
    title: movie["title"],
    overview: movie["overview"],
    poster: movie["poster_path"],
    releaseDate: movie["release_date"]
));
  }
  @override
  void initState() {
    super.initState();
    http.get(this._apiGatewayURL)
        .then((response) => response.body)
        .then(json.decode)
        .then((movies) {
      movies.forEach(_addMovie);
    });
  }

Answer 1

您没有为 ListView 指定 itemCount。因此，如果您有足够的空间来显示比可用项目数量更多的内容，您将尝试在无效索引处访问 _movies。导致这个错误。

尝试添加

new ListView(
   ...
   itemCount: _movie.length