Flutter 我怎样才能深入 json 文件

Question

我想更深入地了解 JSON 文件我需要如何更改代码。

因为我需要更深入地了解数据 -> 资源 -> 项目 -> 标题

My JSON:

{
   "status":"UPDATE",
   "data":{
  "version":"2",
  "modDate":"2021-12-22T17:33:59+0100",
  "languages":[
     "DE",
     "EN"
  ],
  "mapmarker":[
     
  ],
  "resources":[
     {
        "id":241,
        "type":"image",
        "items":[
           {
              "lang":"DE",
              "title":"Labor",
              "file":"uploads\/",
              "size":1923217,
              "modDate":"2019-02-28T18:07:46+0100"
           },
           {
              "lang":"EN",
              "title":"Faust Labor",
              "file":"uploads\/",
              "size":1923217,
              "modDate":"2019-02-28T18:07:46+0100"
           }
        ]
     },

我的不工作实际代码：

Future<void> getDaten() async {
final response =
      await http.get(Uri.parse("https://blabla"));

  final extractedData = json.decode(response.body) as Map<String, dynamic>;

  var deviceData = extractedData["data"] as Map<String, dynamic>;

  var deviceData2 = deviceData["resources"] as Map<String, dynamic>;

  deviceData["items"].forEach((e)=>print(e["text"]));


}

我现有的错误：

Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>' in type cast

我只能转到数据 -> 资源 -> 项目，然后我只能得到这样的字符串

[{lang: DE, title: Schmuck, Uhren und Spiele, file: uploads/Spiele.JPG, size: 774265, modDate: 2021-12-13T16:04:25+0100}]

Answer 1

如果您想提取资源中所有项目的所有 titles，您可以这样做。请注意，我们不需要强制转换我们使用的每个值，因为 dynamic 意味着 Dart 应该忽略我们对对象所做的事情，并期望对 dynamic 的任何调用也是 dynamic:

import 'dart:convert';

void main() {
  dynamic jsonObject = jsonDecode(jsonString);

  final titles = [
    for (Map<String, dynamic> resource in jsonObject['data']['resources'])
      for (Map<String, dynamic> item in resource['items'])
        item['title'] as String
  ];

  titles.forEach(print);
  // Labor
  // Faust Labor
}

const jsonString = '''{
  "status": "UPDATE",
  "data": {
    "version": "2",
    "modDate": "2021-12-22T17:33:59+0100",
    "languages": [
      "DE",
      "EN"
    ],
    "mapmarker": [
    ],
    "resources": [
      {
        "id": 241,
        "type": "image",
        "items": [
          {
            "lang": "DE",
            "title": "Labor",
            "file": "uploads\/",
            "size": 1923217,
            "modDate": "2019-02-28T18:07:46+0100"
          },
          {
            "lang": "EN",
            "title": "Faust Labor",
            "file": "uploads\/",
            "size": 1923217,
            "modDate": "2019-02-28T18:07:46+0100"
          }
        ]
      }
    ]
  }
}
''';

Answer 2

在你的函数下面的行中

  var deviceData = extractedData["data"] as Map<String, dynamic>;

  var deviceData2 = deviceData["resources"] as Map<String, dynamic>;

导致错误，因为在你的 API extractedData["data"] 中 returning 你是 List 但你将其转换为 Map<String, dynamic> 这就是它抛出的原因错误。要像这样解决这个问题：

  var deviceData = extractedData["data"];

  var deviceData2 = deviceData["resources"];

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