为什么我在尝试创建列表时收到 _TypeError？

Question

I have the following JSON that is getting returned from an API call:

{
    "categories": {
       "mortgage": "Mortgage",
       "haircutsClothing": "Haircuts & Clothing",
       "homeRepairMaintenance": "Home Repair & Maintenance"
    },
    "other": {...}
}

And then I have this class acting as a model for the JSON data:

class APIData {
  final Map<String, dynamic> parsedJson;

  APIData({required this.parsedJson});

  factory APIData.fromJson(Map<String, dynamic> parsedJson) {
    List<Category> categories = parsedJson['categories']
        .map((i) => Category.fromJson(i))
        .toList();
    return APIData(parsedJson: parsedJson);
  }
}

class Category {
  final String key;
  final String category;

  Category({required this.key, required this.category});

  factory Category.fromJson(Map<String, dynamic> parsedJson) {
    return Category(key: parsedJson['key'], category: parsedJson['value']);
  }
}

When I run that, I get this error:

_TypeError (type '(dynamic) => Category' is not a subtype of type '(String, dynamic) => MapEntry<dynamic, dynamic>' of 'transform')

What am I doing wrong that is causing this error?

Answer 1

method.map on Map object has to return Map object too.

try this

final categoriesMap = parsedJson['categories'] as Map;

final List<Category> categories =
        categoriesMap.entries
        .map((e) => Category(key: e.key, category: e.value))
        .toList();

entries from a Map returns an Iterable of Map Entry. then you can iterate through it and use key and value properties.