在Dart中解析具有嵌套对象数组的JSON？

Question

我正在制作一个Flutter应用程序,我正在使用The MovieDB api来获取数据.当我打电话给api并要求一部特定的电影时,这是我得到的一般格式:

{
   "adult": false,
    "backdrop_path": "/wrqUiMXttHE4UBFMhLHlN601MZh.jpg",
    "belongs_to_collection": null,
    "budget": 120000000,
    "genres": [
        {
            "id": 28,
            "name": "Action"
        },
        {
            "id": 12,
            "name": "Adventure"
        },
        {
            "id": 878,
            "name": "Science Fiction"
        }
    ],
    "homepage": "http://www.rampagethemovie.com",
    "id": 427641,
    "imdb_id": "tt2231461",
    "original_language": "en",
    "original_title": "Rampage",
...
}

我已经设置了一个模型类来解析它,并且类定义如下:

import 'dart:async';

class MovieDetail {
  final String title;
  final double rating;
  final String posterArtUrl;
  final backgroundArtUrl;
  final List<Genre> genres;
  final String overview;
  final String tagline;
  final int id;

  const MovieDetail(
      {this.title, this.rating, this.posterArtUrl, this.backgroundArtUrl, this.genres, this.overview, this.tagline, this.id});

  MovieDetail.fromJson(Map jsonMap)
      : title = jsonMap['title'],
        rating = jsonMap['vote_average'].toDouble(),
        posterArtUrl = "http://image.tmdb.org/t/p/w342" + jsonMap['backdrop_path'],
        backgroundArtUrl = "http://image.tmdb.org/t/p/w500" + jsonMap['poster_path'],
        genres = (jsonMap['genres']).map((i) => Genre.fromJson(i)).toList(),
        overview = jsonMap['overview'],
        tagline = jsonMap['tagline'],
        id = jsonMap['id'];
}
class Genre {
  final int id;
  final String genre;

  const Genre(this.id, this.genre);

  Genre.fromJson(Map jsonMap)
    : id = jsonMap['id'],
      genre = jsonMap['name'];
}

我的问题是我无法从JSON中正确解析该类型.当我获得JSON并将其传递给我的模型类时,我收到以下错误:

I/flutter (10874): type 'List<dynamic>' is not a subtype of type 'List<Genre>' where
I/flutter (10874):   List is from dart:core
I/flutter (10874):   List is from dart:core
I/flutter (10874):   Genre is from package:flutter_app_first/models/movieDetail.dart

我认为这会有效,因为我为Genre对象创建了一个不同的类,并将JSON数组作为列表传递.我不明白怎么List<dynamic>不是孩子,List<Genre>因为关键词不是dynamic暗示任何对象？有谁知道如何将嵌套的JSON数组解析为自定义对象？

Answer 1

尝试 genres = (jsonMap['genres'] as List).map((i) => Genre.fromJson(i)).toList()

问题:map没有强制转换的调用使它成为动态调用,这意味着返回类型Genre.fromJson也是动态的(不是流派).

请查看https://flutter.io/json/以获取一些提示.

有一些解决方案,比如https://pub.dartlang.org/packages/json_serializable,这使得这更容易

Answer 2

我认为JSONtoDart 转换器非常有用，必须尝试...