如何从列表映射Flutter JSON字符串?
问题内容:
我已成功从YouTube JSON URL中将响应打印为字符串,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
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)
任何Card Info变量都会抛出上述错误。
****的日志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}}]}
***使用循环语句更新
这是我for loop
的代码,返回type 'String' is not a subtype of type 'int' of 'index'
错误…
Map data = JSON.decode(response);
var videos = data['items'];
for (var items in videos['snippet']){
print(items);
}
遍历循环可以items in videos
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。
问题答案:
它看起来像data['items']
一个List
(即JSON阵列),而不是一个Map
。
您可以使用列表推导方法为您提供帮助:
final items = (data['items'] as List).map((i) => new CardInfo.fromJson(i));
for (final item in items) {
print(item.id);
}