This is the error I get when request data from api - Performing hot restart... Syncing files to device sdk gphone x86 64 arm64... Restarted application in 777ms. E/flutter (21101): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: NoSuchMethodError: The method '[]' was called on null. E/flutter (21101): Receiver: null E/flutter (21101): Tried calling: E/flutter (21101): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:38:5) E/flutter (21101): #1 new Recipe.fromJson (package:food_recipe_app_1/models/recipe.dart:16:19) E/flutter (21101): #2 Recipe.recipesFromSnapshot. (package:food_recipe_app_1/models/recipe.dart:25:21) E/flutter (21101): #3 MappedListIterable.elementAt (dart:_internal/iterable.dart:413:31) E/flutter (21101): #4 ListIterator.moveNext (dart:_internal/iterable.dart:342:26) E/flutter (21101): #5 new _GrowableList._ofEfficientLengthIterable (dart:core-patch/growable_array.dart:189:27) E/flutter (21101): #6 new _GrowableList.of (dart:core-patch/growable_array.dart:150:28) E/flutter (21101): #7 new List.of (dart:core-patch/array_patch.dart:51:28) E/flutter (21101): #8 ListIterable.toList (dart:_internal/iterable.dart:213:44) E/flutter (21101): #9 Recipe.recipesFromSnapshot (package:food_recipe_app_1/models/recipe.dart:26:8) E/flutter (21101): #10 RecipeApi.getRecipe (package:food_recipe_app_1/models/recipe.api.dart:26:19) E/flutter (21101): E/flutter (21101): #11 _HomePageState.getRecipes (package:food_recipe_app_1/views/home.dart:25:16) E/flutter (21101): E/flutter (21101):

class Recipe {
  final String name;
  final String images;
  final double rating;
  final String totalTime;

  Recipe({
    this.name,
    this.images,
    this.rating,
    this.totalTime,
  });

  factory Recipe.fromJson(dynamic json) {
    return Recipe(
        name: json['name'] as String,
        images: json['images'][0]['hostedLargeUrl'] as String,
        rating: json['rating'] as double,
        totalTime: json['totalTime'] as String
    );
  }

  static List<Recipe> recipesFromSnapshot(List snapshot) {
    return snapshot.map((data) {
      return Recipe.fromJson(data);
    }).toList();
  }
  @override
  String toString() {
    return 'Recipe {name: $name, image: $images, rating: $rating, totalTime: $totalTime}';
  }
}

CodePudding user response：

Either json is null, or json['images'] returns null. There are other ways to do it, here is one option if you don't want to allow null values:

factory Recipe.fromJson(dynamic json) {
  if (json == null) return Recipe.empty();
  return Recipe(
      name: json['name'] ?? '',
      images: json['images']?[0]['hostedLargeUrl'] ?? '',
      rating: json['rating'] ?? 0,
      totalTime: json['totalTime'] ?? ''
  );
}

factory Recipe.empty() => Recipe(name: '', images: '', rating: '', totalTime: '');

CodePudding user response：

You haven't included enough code to be sure of where your error is exactly, but here is an example of what is happening so you can find it:

List<String>? _list;

right now _list is null.

If I call String _string = _list[0];

I will get the error you are experiencing. So your list is null somewhere.