Блог

Я создаю приложение для фильмов, в котором у меня есть список плакатов, загруженных с помощью TMDB, с использованием библиотеки infinite_scroll_pagination 3.0.1 1. Первый набор данных загружается хорошо, но после прокрутки и перед загрузкой второго набора данных я получаю следующее исключение.

 "Invalid argument(s) (input): Must not be null"
 

Во время ручной отладки я обнаружил, что исключение возникает в results = Movie.fromJson(jsonMap).results; in services.dart (файл модели фильма). Любая помощь будет признательна.

movie_page.дарт

 import 'dart:async';

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:infinite_scroll_pagination/infinite_scroll_pagination.dart';
import 'package:zlikx/services.dart';

import 'movies.dart';

class MoviesPage extends StatefulWidget {
  @override
  State<MoviesPage> createState() => _MoviesPageState();
}

class _MoviesPageState extends State<MoviesPage> {
  static const _pageSize = 20;
  final PagingController<int, Result> _pagingController = PagingController(firstPageKey: 1);

  @override
  void initState() {
    print('insideinit');
    _pagingController.addPageRequestListener((pageKey) {
      _fetchPage(pageKey);
    });
    super.initState();
  }

  Future<void> _fetchPage(int pageKey) async {
    try {
      final newItems = await Services().fetchmovies(pageKey);
      print('newItems.length'   newItems.length.toString());
      final isLastPage = newItems.length < _pageSize;
      if (isLastPage) {
        print('inside is last page');
        _pagingController.appendLastPage(newItems);
      } else {
        print('pageKey'   pageKey.toString());
        final nextPageKey = pageKey   1;
        print('nextPageKey :'   nextPageKey.toString());
        _pagingController.appendPage(newItems, nextPageKey);
      }
    } catch (error) {
      _pagingController.error = error;
      print('Paging Error: '   error.toString());
    }
  }

  @override
  Widget build(BuildContext context) => RefreshIndicator(
        onRefresh: () => Future.sync(
          () => _pagingController.refresh(),
        ),
        child: PagedGridView(
          gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 2, childAspectRatio: 1 / 1.5),
          pagingController: _pagingController,
          builderDelegate: PagedChildBuilderDelegate<Result>(
            itemBuilder: (context, result, index) {
              return Image.network(
                'https://image.tmdb.org/t/p/w500'   result.posterPath,
                fit: BoxFit.fill,
              );
            },
          ),
          padding: const EdgeInsets.all(16),
        ),
      );

  @override
  void dispose() {
    _pagingController.dispose();
    super.dispose();
  }
}


 

услуги.дротик

 import 'dart:convert';

import 'package:http/http.dart' as http;
import 'movies.dart';

class Services {
  static const String movie_url = "https://api.themoviedb.org/3/movie/popular?api_key=[KEY_HIDDEN]amp;language=en-USamp;page=1";
  static const String popular_movies = "https://api.themoviedb.org/3/movie/popular?api_key=[KEY_HIDDEN]bamp;language=en-USamp;page=";

  Future<Movie> getMovies() async {
    var client = http.Client();
    var moviesModel;

    try {
      var response = await client.get(Uri.parse(movie_url));
      if (response.statusCode == 200) {
        var jsonString = response.body;
        var jsonMap = json.decode(jsonString);

        moviesModel = Movie.fromJson(jsonMap);
      }
      // ignore: non_constant_identifier_names
    } catch (Exception) {
      print(Exception.toString());
      return moviesModel;
    }

    return moviesModel;
  }

  Future<List<Result>> fetchmovies(int pageKey) async {
    var client = http.Client();
    var results;
    print('Inside fetchmovies');
    try {
      print('pageKey: '   pageKey.toString());
      var urlToHit = Uri.parse(popular_movies   pageKey.toString());
      print(urlToHit);
      var response = await client.get(urlToHit);
      print('response.body: '   response.body.toString());
      if (response.statusCode == 200) {
        var jsonString = response.body;
        var jsonMap = json.decode(jsonString);
        print('jsonMap: '   jsonMap.toString());
        results = Movie.fromJson(jsonMap).results;
        print('results'   results.toString());
      } else {
        print('response.statusCode: '   response.statusCode.toString());
      }
      // ignore: non_constant_identifier_names
    } catch (Exception) {
      print('fetch movies Exception '   Exception.toString());
      return results;
    }

    return results;
  }
}

 

My model class movies.dart

 // To parse this JSON data, do
//
//     final movie = movieFromJson(jsonString);

import 'dart:convert';

Movie movieFromJson(String str) => Movie.fromJson(json.decode(str));

String movieToJson(Movie data) => json.encode(data.toJson());

class Movie {
    Movie({
        this.page,
        this.results,
        this.totalPages,
        this.totalResults,
    });

    int page;
    List<Result> results;
    int totalPages;
    int totalResults;

    factory Movie.fromJson(Map<String, dynamic> json) => Movie(
        page: json["page"],
        results: List<Result>.from(json["results"].map((x) => Result.fromJson(x))),
        totalPages: json["total_pages"],
        totalResults: json["total_results"],
    );

    Map<String, dynamic> toJson() => {
        "page": page,
        "results": List<dynamic>.from(results.map((x) => x.toJson())),
        "total_pages": totalPages,
        "total_results": totalResults,
    };
}

class Result {
    Result({
        this.adult,
        this.backdropPath,
        this.genreIds,
        this.id,
        this.originalLanguage,
        this.originalTitle,
        this.overview,
        this.popularity,
        this.posterPath,
        this.releaseDate,
        this.title,
        this.video,
        this.voteAverage,
        this.voteCount,
    });

    bool adu<
    String backdropPath;
    List<int> genreIds;
    int id;
    String originalLanguage;
    String originalTitle;
    String overview;
    double popularity;
    String posterPath;
    DateTime releaseDate;
    String title;
    bool video;
    double voteAverage;
    int voteCount;

    factory Result.fromJson(Map<String, dynamic> json) => Result(
        adult: json["adult"],
        backdropPath: json["backdrop_path"],
        genreIds: List<int>.from(json["genre_ids"].map((x) => x)),
        id: json["id"],
        originalLanguage: json["original_language"],
        originalTitle: json["original_title"],
        overview: json["overview"],
        popularity: json["popularity"].toDouble(),
        posterPath: json["poster_path"],
        releaseDate: DateTime.parse(json["release_date"]),
        title: json["title"],
        video: json["video"],
        voteAverage: json["vote_average"].toDouble(),
        voteCount: json["vote_count"],
    );

    Map<String, dynamic> toJson() => {
        "adult": adult,
        "backdrop_path": backdropPath,
        "genre_ids": List<dynamic>.from(genreIds.map((x) => x)),
        "id": id,
        "original_language": originalLanguage,
        "original_title": originalTitle,
        "overview": overview,
        "popularity": popularity,
        "poster_path": posterPath,
        "release_date": "${releaseDate.year.toString().padLeft(4, '0')}-${releaseDate.month.toString().padLeft(2, '0')}-${releaseDate.day.toString().padLeft(2, '0')}",
        "title": title,
        "video": video,
        "vote_average": voteAverage,
        "vote_count": voteCount,
    };
}

 

Console output

 I/flutter (14202): pageKey: 2
I/flutter (14202): https://api.themoviedb.org/3/movie/popular?api_key=9b31264aec7cd32ff6ff94ebceecb01bamp;language=en-USamp;page=2
I/flutter (14202): response.body: {"page":2,"results":[{"adult":false,"backdrop_path":"/70AV2Xx5FQYj20labp0EGdbjI6E.jpg","genre_ids":[28,80],"id":637649,"original_language":"en","original_title":"Wrath of Man","overview":"A cold and mysterious new security guard for a Los Angeles cash truck company surprises his co-workers when he unleashes precision skills during a heist. The crew is left wondering who he is and where he came from. Soon, the marksman's ultimate motive becomes clear as he takes dramatic and irrevocable steps to settle a score.","popularity":642.634,"poster_path":"/YxopfHpsCV1oF8CZaL4M3Eodqa.jpg","release_date":"2021-04-22","title":"Wrath of Man","video":false,"vote_average":8,"vote_count":308},{"adult":false,"backdrop_path":"/7HtvmsLrDeiAgDGa1W3m6senpfE.jpg","genre_ids":[12,16,10751],"id":681260,"original_language":"en","original_title":"Maya the Bee: The Golden Orb","overview":"When Maya, a headstrong little bee, and her best friend Willi, rescue an ant princess they find themselves in the middle of an epic b
I/flutter (14202): jsonMap: {page: 2, results: [{adult: false, backdrop_path: /70AV2Xx5FQYj20labp0EGdbjI6E.jpg, genre_ids: [28, 80], id: 637649, original_language: en, original_title: Wrath of Man, overview: A cold and mysterious new security guard for a Los Angeles cash truck company surprises his co-workers when he unleashes precision skills during a heist. The crew is left wondering who he is and where he came from. Soon, the marksman's ultimate motive becomes clear as he takes dramatic and irrevocable steps to settle a score., popularity: 642.634, poster_path: /YxopfHpsCV1oF8CZaL4M3Eodqa.jpg, release_date: 2021-04-22, title: Wrath of Man, video: false, vote_average: 8, vote_count: 308}, {adult: false, backdrop_path: /7HtvmsLrDeiAgDGa1W3m6senpfE.jpg, genre_ids: [12, 16, 10751], id: 681260, original_language: en, original_title: Maya the Bee: The Golden Orb, overview: When Maya, a headstrong little bee, and her best friend Willi, rescue an ant princess they find themselves in the middle of an epic bug battle that will take t
I/flutter (14202): fetch movies Exception Invalid argument(s) (input): Must not be null
I/flutter (14202): Paging Error: NoSuchMethodError: The getter 'length' was called on null.
I/flutter (14202): Receiver: null
I/flutter (14202): Tried calling: length
D/ViewRootImpl[MainActivity](14202): windowFocusChanged hasFocus=false inTouchMode=true

 

Response Sample

 {
  "page": 2,
  "results": [
    {
      "adult": false,
      "backdrop_path": "/z2UtGA1WggESspi6KOXeo66lvLx.jpg",
      "genre_ids": [
        18,
        878,
        53
      ],
      "id": 520763,
      "original_language": "en",
      "original_title": "A Quiet Place Part II",
      "overview": "Following the events at home, the Abbott family now face the terrors of the outside world. Forced to venture into the unknown, they realize that the creatures that hunt by sound are not the only threats that lurk beyond the sand path.",
      "popularity": 690.813,
      "poster_path": "/4q2hz2m8hubgvijz8Ez0T2Os2Yv.jpg",
      "release_date": "2021-05-21",
      "title": "A Quiet Place Part II",
      "video": false,
      "vote_average": 7.5,
      "vote_count": 58
    },
    {
      "adult": false,
      "backdrop_path": "/70AV2Xx5FQYj20labp0EGdbjI6E.jpg",
      "genre_ids": [
        28,
        80
      ],
      "id": 637649,
      "original_language": "en",
      "original_title": "Wrath of Man",
      "overview": "A cold and mysterious new security guard for a Los Angeles cash truck company surprises his co-workers when he unleashes precision skills during a heist. The crew is left wondering who he is and where he came from. Soon, the marksman's ultimate motive becomes clear as he takes dramatic and irrevocable steps to settle a score.",
      "popularity": 899.688,
      "poster_path": "/YxopfHpsCV1oF8CZaL4M3Eodqa.jpg",
      "release_date": "2021-04-22",
      "title": "Wrath of Man",
      "video": false,
      "vote_average": 8,
      "vote_count": 367
    },
    {
      "adult": false,
      "backdrop_path": "/7HtvmsLrDeiAgDGa1W3m6senpfE.jpg",
      "genre_ids": [
        12,
        16,
        10751
      ],
      "id": 681260,
      "original_language": "en",
      "original_title": "Maya the Bee: The Golden Orb",
      "overview": "When Maya, a headstrong little bee, and her best friend Willi, rescue an ant princess they find themselves in the middle of an epic bug battle that will take them to strange new worlds and test their friendship to its limits.",
      "popularity": 890.077,
      "poster_path": "/tMS2qcbhbkFpcwLnbUE9o9IK4HH.jpg",
      "release_date": "2021-01-07",
      "title": "Maya the Bee: The Golden Orb",
      "video": false,
      "vote_average": 6.6,
      "vote_count": 32
    },
    {
      "adult": false,
      "backdrop_path": "/5Zv5KmgZzdIvXz2KC3n0MyecSNL.jpg",
      "genre_ids": [
        28,
        53,
        80
      ],
      "id": 634528,
      "original_language": "en",
      "original_title": "The Marksman",
      "overview": "Jim Hanson’s quiet life is suddenly disturbed by two people crossing the US/Mexico border – a woman and her young son – desperate to flee a Mexican cartel. After a shootout leaves the mother dead, Jim becomes the boy’s reluctant defender. He embraces his role as Miguel’s protector and will stop at nothing to get him to safety, as they go on the run from the relentless assassins.",
      "popularity": 739.328,
      "poster_path": "/6vcDalR50RWa309vBH1NLmG2rjQ.jpg",
      "release_date": "2021-01-15",
      "title": "The Marksman",
      "video": false,
      "vote_average": 7.4,
      "vote_count": 505
    },
    {
      "adult": false,
      "backdrop_path": "/jFINtstDUh0vHOGImpMAmLrPcXy.jpg",
      "genre_ids": [
        28,
        27,
        35
      ],
      "id": 643586,
      "original_language": "en",
      "original_title": "Willy's Wonderland",
      "overview": "When his car breaks down, a quiet loner agrees to clean an abandoned family fun center in exchange for repairs. He soon finds himself waging war against possessed animatronic mascots while trapped inside Willy's Wonderland.",
      "popularity": 700.784,
      "poster_path": "/keEnkeAvifw8NSEC4f6WsqeLJgF.jpg",
      "release_date": "2021-02-12",
      "title": "Willy's Wonderland",
      "video": false,
      "vote_average": 6.7,
      "vote_count": 227
    },
    {
      "adult": false,
      "backdrop_path": "/sPeqIdCYvcmeZe5fCu7JgMnf1HL.jpg",
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        35,
        878
      ],
      "id": 825597,
      "original_language": "en",
      "original_title": "Maggie Simpson in The Force Awakens from Its Nap",
      "overview": "In a daycare far, far away… but still in Springfield, Maggie is on an epic quest for her stolen pacifier. Her adventure brings her face-to-face with young Padawans, Sith Lords, familiar droids, Rebel scum, and an ultimate battle against the dark side, in this original short celebrating the Star Wars galaxy.",
      "popularity": 792.587,
      "poster_path": "/2xnf2ZaGXudvgBKPtVXMkNeooh1.jpg",
      "release_date": "2021-05-04",
      "title": "Maggie Simpson in The Force Awakens from Its Nap",
      "video": false,
      "vote_average": 6.8,
      "vote_count": 49
    },
    {
      "adult": false,
      "backdrop_path": "/xXHZeb1yhJvnSHPzZDqee0zfMb6.jpg",
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        80
      ],
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      "poster_path": "/bOFaAXmWWXC3Rbv4u4uM9ZSzRXP.jpg",
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      "title": "F9",
      "video": false,
      "vote_average": 8.3,
      "vote_count": 66
    },
    {
      "adult": false,
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        27,
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      ],
      "id": 647302,
      "original_language": "en",
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      ],
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      "title": "Monster Hunter",
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    },
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      ],
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      "poster_path": "/8XZI9QZ7Pm3fVkigWJPbrXCMzjq.jpg",
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    },
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      "adult": false,
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    },
    {
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      ],
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      "original_language": "en",
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      "popularity": 577.181,
      "poster_path": "/vX1XLbrHxpryX9EOWI3akbasz6c.jpg",
      "release_date": "2021-04-08",
      "title": "Instructions for Su",
      "video": false,
      "vote_average": 7.8,
      "vote_count": 45
    },
    {
      "adult": false,
      "backdrop_path": "/kf456ZqeC45XTvo6W9pW5clYKfQ.jpg",
      "genre_ids": [
        10751,
        16,
        35,
        18,
        10402,
        14
      ],
      "id": 508442,
      "original_language": "en",
      "original_title": "Soul",
      "overview": "Joe Gardner is a middle school teacher with a love for jazz music. After a successful gig at the Half Note Club, he suddenly gets into an accident that separates his soul from his body and is transported to the You Seminar, a center in which souls develop and gain passions before being transported to a newborn child. Joe must enlist help from the other souls-in-training, like 22, a soul who has spent eons in the You Seminar, in order to get back to Earth.",
      "popularity": 503.845,
      "poster_path": "/hm58Jw4Lw8OIeECIq5qyPYhAeRJ.jpg",
      "release_date": "2020-12-25",
      "title": "Soul",
      "video": false,
      "vote_average": 8.3,
      "vote_count": 6110
    },
    {
      "adult": false,
      "backdrop_path": "/aMFl4wOPhJ7NVua6SgU9zIJvFSx.jpg",
      "genre_ids": [
        16,
        10751,
        35,
        12,
        10770
      ],
      "id": 755812,
      "original_language": "fr",
      "original_title": "Miraculous World : New York, les héros unis",
      "overview": "During a school field trip, Ladybug and Cat Noir meet the American superheroes, whom they have to save from an akumatised super-villain. They discover that Miraculous exist in the United States too.",
      "popularity": 469.299,
      "poster_path": "/19kfvGktytDZInUmpv3WlaHoTxP.jpg",
      "release_date": "2020-09-26",
      "title": "Miraculous World: New York, United HeroeZ",
      "video": false,
      "vote_average": 8.3,
      "vote_count": 707
    }
  ],
  "total_pages": 500,
  "total_results": 10000
}
 

обновленная модель

 // To parse this JSON data, do
//
//     final movie = movieFromJson(jsonString);

import 'dart:convert';

Movie movieFromJson(String str) => Movie.fromJson(json.decode(str));

String movieToJson(Movie data) => json.encode(data.toJson());

class Movie {
  Movie({
    required this.page,
    required this.results,
    required this.totalPages,
    required this.totalResults,
  });

  int page;
  List<Result> results;
  int totalPages;
  int totalResults;

  factory Movie.fromJson(Map<String, dynamic> json) => Movie(
        page: json["page"],
        results: List<Result>.from(json["results"].map((x) => Result.fromJson(x))),
        totalPages: json["total_pages"],
        totalResults: json["total_results"],
      );

  Map<String, dynamic> toJson() => {
        "page": page,
        "results": List<dynamic>.from(results.map((x) => x.toJson())),
        "total_pages": totalPages,
        "total_results": totalResults,
      };
}

class Result {
  Result({
    required this.adult,
    this.backdropPath,
    this.genreIds,
    this.id,
    this.originalLanguage,
    this.originalTitle,
    this.overview,
    this.popularity,
    this.posterPath,
    this.releaseDate,
    this.title,
    this.video,
    this.voteAverage,
    this.voteCount,
  });

  bool adu<
  String? backdropPath;
  List<int>? genreIds;
  int? id;
  String? originalLanguage;
  String? originalTitle;
  String? overview;
  double? popularity;
  String? posterPath;
  DateTime? releaseDate;
  String? title;
  bool? video;
  double? voteAverage;
  int? voteCount;

  factory Result.fromJson(Map<String, dynamic> json) => Result(
        adult: json["adult"],
        backdropPath: json["backdrop_path"],
        genreIds: List<int>.from(json["genre_ids"].map((x) => x)),
        id: json["id"],
        originalLanguage: json["original_language"],
        originalTitle: json["original_title"],
        overview: json["overview"],
        popularity: json["popularity"].toDouble(),
        posterPath: json["poster_path"],
        releaseDate: DateTime.parse(json["release_date"]),
        title: json["title"],
        video: json["video"],
        voteAverage: json["vote_average"].toDouble(),
        voteCount: json["vote_count"],
      );

  Map<String, dynamic> toJson() => {
        "adult": adult,
        "backdrop_path": backdropPath,
        "genre_ids": List<dynamic>.from(genreIds!.map((x) => x)),
        "id": id,
        "original_language": originalLanguage,
        "original_title": originalTitle,
        "overview": overview,
        "popularity": popularity,
        "poster_path": posterPath,
        "release_date": "${releaseDate!.year.toString().padLeft(4, '0')}-${releaseDate!.month.toString().padLeft(2, '0')}-${releaseDate!.day.toString().padLeft(2, '0')}",
        "title": title,
        "video": video,
        "vote_average": voteAverage,
        "vote_count": voteCount,
      };
}

 

Добавлена ссылка на github для справки https://github.com/nizamudeenms/ZlikxFlutter/

В Result объекте с идентификатором 385687 у вас есть свойство backdrop_path , равное нулю. Настройте свой Result объект и сделайте свойство недействительным:

String? backdropPath;