如何从列表映射Flutter JSON字符串?

问题描述

我已成功从YouTube JSON URL中将响应打印为String，但是当我尝试通过项目"进行序列化时，出现以下错误Unhandled exception: type 'List' is not a subtype of type 'Map' of 'json' where List is from dart:core Map is from dart:core

I'm successfully printing my response as String from my YouTube JSON url, but when I try to serialize through the "items" I get the following error Unhandled exception: type 'List' is not a subtype of type 'Map' of 'json' where List is from dart:core Map is from dart:core

这是我的代码...

class CardInfo {
  //Constructor
  String id;
  String description;
  String role;
  //int score;

  CardInfo.fromJson(Map json) {
    this.id = json['vieoId'];
    this.description = json['description'];
    this.role = json['title'];
    //this.score = json['score'];
  }
}

Future getData() async {
    String url = 'YouTube url';
    var httpClient  = createHttpClient();
    var response = await httpClient.get(url);
    Map data = JSON.decode(response.body);
    //String ip = data['items'];
    var ci = new CardInfo.fromJson(data['items']);

    //print(data['items']);
    print(ci.id);
    //print(ci.description);
    //print(ci.role);

    if (!mounted) return;


    setState(() {});

  }

print(data['items']正在打印，但是print(ci.id)或任何Card Info变量都会引发上述错误.

print(data['items'] is printing, but print(ci.id) or any Card Info variables throws the above error.

**** print(data)的日志；

**** Log of print(data);

{kind: youtube#searchListResponse, etag: "VPWTmrH7dFmi4s1RqrK4tLejnRI/P9wyOxsXEuXOCvj7znCun2-EykU", nextPageToken: CAMQAA, regionCode: US, pageInfo: {totalResults: 1000000, resultsPerPage: 3}, items: [{kind: youtube#searchResult, etag: "VPWTmrH7dFmi4s1RqrK4tLejnRI/Csl1kQhnOsbs0j4_336zJAN176k", id: {kind: youtube#video, videoId: e3pUxU_bE6w}, snippet: {publishedAt: 2017-09-14T09:43:17.000Z, channelId: UCbD8EppRX3ZwJSou-TVo90A, title: [PRISTIN - We Like] KPOP TV Show | M COUNTDOWN 170914 EP.541, description: KPOP Chart Show M COUNTDOWN | EP.541 - PRISTIN - We Like ▷Watch more video clips: http://MCOUNTDOWN-KPOP2017 [Kor Ver.] 프리티 ..., thumbnails: {default: {url: https://i.ytimg.com/vi/e3pUxU_bE6w/default.jpg, width: 120, height: 90}, medium: {url: https://i.ytimg.com/vi/e3pUxU_bE6w/mqdefault.jpg, width: 320, height: 180}, high: {url: https://i.ytimg.com/vi/e3pUxU_bE6w/hqdefault.jpg, width: 480, height: 360}}, channelTitle: Mnet K-POP, liveBroadcastContent: none}}, {kind: youtube#searchResult, etag: "VPWTmrH7dFmi4s1RqrK4tLejnRI/1JCCNBPNbFeusCp_9-pl4i8q5OU", id: {kind: youtube#video, videoId: Cc4hO9RLdl4}, snippet: {publishedAt: 2017-09-14T10:37:29.000Z, channelId: UCbD8EppRX3ZwJSou-TVo90A, title: [EXO - Power] KPOP TV Show | M COUNTDOWN 170914 EP.541, description: KPOP Chart Show M COUNTDOWN | EP.541 - EXO - Power ▷Watch more video clips: http://MCOUNTDOWN-KPOP2017 [Kor Ver.] Power Up! '#EXO' 여기 ..., thumbnails: {default: {url: https://i.ytimg.com/vi/Cc4hO9RLdl4/default.jpg, width: 120, height: 90}, medium: {url: https://i.ytimg.com/vi/Cc4hO9RLdl4/mqdefault.jpg, width: 320, height: 180}, high: {url: https://i.ytimg.com/vi/Cc4hO9RLdl4/hqdefault.jpg, width: 480, height: 360}}, channelTitle: Mnet K-POP, liveBroadcastContent: none}}, {kind: youtube#searchResult, etag: "VPWTmrH7dFmi4s1RqrK4tLejnRI/ZnYC4e5evyfldkM67HsDuV8Yh3E", id: {kind: youtube#video, videoId: BBcOM25wrVo}, snippet: {publishedAt: 2017-08-18T15:21:48.000Z, channelId: UCtFtO4By4czgkYGvEXvJu0A, title: Kpop Banned Dance: MV vs LIVE, description: Kpop Banned Dance: MV vs LIVE Koreas biggest broadcasting companies has strict rules and standards on what lyrics and dances moves can be performed., thumbnails: {default: {url: https://i.ytimg.com/vi/BBcOM25wrVo/default.jpg, width: 120, height: 90}, medium: {url: https://i.ytimg.com/vi/BBcOM25wrVo/mqdefault.jpg, width: 320, height: 180}, high: {url: https://i.ytimg.com/vi/BBcOM25wrVo/hqdefault.jpg, width: 480, height: 360}}, channelTitle: Kpop Corn, liveBroadcastContent: none}}]}

***使用循环声明更新

*** UPDATE WITH FOR LOOP STATEMENT

这是我的for loop的代码，返回了type 'String' is not a subtype of type 'int' of 'index'错误...

Here is code for my for loop that's returning a type 'String' is not a subtype of type 'int' of 'index' error...

Map data = JSON.decode(response);
var videos = data['items'];
for (var items in videos['snippet']){
      print(items);
    }

在items in videos中循环播放，可为我寻找的3个视频提供3个单独的条目-包括摘要.尝试获取各个片段失败.请指出正确的方向.

Running a loop through items in videos gives me 3 separate entries for the 3 videos I'm looking for - including snippets. Trying to get the individual snippets is failing. Please point me in the right direction.

推荐答案

看起来data['items']是List(即JSON数组)，而不是Map.

It looks like data['items'] is a List (i.e. a JSON Array), not a Map.

您可以在这里使用列表理解方法来提供帮助:

You can use list comprehension methods to help here:

final items = (data['items'] as List).map((i) => new CardInfo.fromJson(i));
for (final item in items) {
  print(item.id);
}

这篇关于如何从列表映射Flutter JSON字符串?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！