Dart 2和解析json [英] Dart 2 and parsing json

问题描述

我正在尝试使用Dart 2 for web将json解析为产品列表.

Im trying to parse json into a list of Products using Dart 2 for web.

我有以下课程:

class Product {

  final String Problem;

  final String Owner;

  final String Description;

  const Product({
    this.Problem, 
    this.Owner,
    this.Description,
  });


  factory Product.parse(Map<String, dynamic> json) {
    print(json);
    return new Product(
      Problem: json["Problem"],
      Owner: json["Owner"],
      Description: json["Description"]
    );
  }
}

我正在尝试使用以下方法来解析它:

And I am trying to parse this using:

Stream<Product> getProducts() async* {
    final payload = await HttpRequest.getString("products.json");
    print(payload);
    //var _json = (json.decode(payload));
    print("break");
    var list = json.decode(payload);
    print(list);
    //print(list);
    final productList = (json.decode(payload) as List).cast<Map<String, dynamic>>();

  }

但是此操作因以下错误而失败:

However this fails with this error:

例外:类型"_JsonMap"不是预期类型的​​子类型列表".

EXCEPTION: Type '_JsonMap' is not a subtype of expected type 'List'.

在调试时，我看到我有一个 list [Symbol(_original)] ，但是当我尝试对此求值时，我返回的是未定义的.

I can see that I have a list[Symbol(_original)] when I debug, but when I try to evaluate this, I returns as undefined.

我也尝试过

• 列表列表= json.decode(有效载荷)作为列表;
• List< dynamic>list = json.decode(payload);
• List< dynamic>list = json.decode(payload)as List< dynamic> ;;
• var list =(json.decode(payload)).cast< Map< String，dynamic>>>>>>();
• var list =(json.decode(payload)).cast< Map<动态，动态>>>>();

但出现相同的错误.

{
    "Product_One": {
        "Owner": "test",
        "Description": "test description",
        "Theme_Objective": "test objective",
        "Technical_details": "test technical details",
        "Problem": "test",
        "Solution": "test"
    }
}

推荐答案

您的JSON不包含任何列表，而是所有地图.当您尝试将 Map 强制转换为 List 时，由于映射不是列表，因此它必须失败.

Your JSON does not contain any list, it's all maps. When you try to cast a Map to List, it has to fail since maps are not lists.

也许您想做:

final productList = (jsonDecode(payload) as Map).values.toList();

这为您提供了产品地图列表，但没有您似乎从未使用过的名称.

This gives you a list of the product maps, without the names that you don't appear to be using anyway.

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