flutter - NoSuchMethodError JSON

Question

运行以下代码时出现 NoSuchMethodError - 我想从 JSON url 打印出轨道标题 - 我错过了什么吗？

import 'dart:async';
import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

Future<Track> fetchPost() async {
  final response =
  await http.get('http://139.59.108.222:2199/rpc/drn1/streaminfo.get');

  if (response.statusCode == 200) {
    // If the call to the server was successful, parse the JSON.
    return Track.fromJson(json.decode(response.body));
  } else {
    // If that call was not successful, throw an error.
    throw Exception('Failed to load post');
  }
}

class Track {
  String artist;
  String title;
  String album;
  int royaltytrackid;
  dynamic started;
  int id;
  int length;
  Playlist playlist;
  String buyurl;
  String imageurl;

  Track({
    this.artist,
    this.title,
    this.album,
    this.royaltytrackid,
    this.started,
    this.id,
    this.length,
    this.playlist,
    this.buyurl,
    this.imageurl,
  });

  factory Track.fromJson(Map<String, dynamic> json) => Track(
    artist: json["artist"],
    title: json["title"],
    album: json["album"],
    royaltytrackid: json["royaltytrackid"],
    started: json["started"],
    id: json["id"],
    length: json["length"],
    playlist: Playlist.fromJson(json["playlist"]),
    buyurl: json["buyurl"],
    imageurl: json["imageurl"],
  );

  Map<String, dynamic> toJson() => {
    "artist": artist,
    "title": title,
    "album": album,
    "royaltytrackid": royaltytrackid,
    "started": started,
    "id": id,
    "length": length,
    "playlist": playlist.toJson(),
    "buyurl": buyurl,
    "imageurl": imageurl,
  };
}


class Playlist {
  int id;
  String title;

  Playlist({
    this.id,
    this.title,
  });

  factory Playlist.fromJson(Map<String, dynamic> json) => Playlist(
    id: json["id"],
    title: json["title"],
  );

  Map<String, dynamic> toJson() => {
    "id": id,
    "title": title,
  };
}



void main() => runApp(MyPosts(track: fetchPost()));

class MyPosts extends StatelessWidget {
  final Future<Track> track;

  MyPosts({Key key, this.track}) : super(key: key);


  @override
  Widget build(BuildContext context) {
    double c_width = MediaQuery.of(context).size.width;
    return Container(
      padding: const EdgeInsets.all(16.0),
      width: c_width,
      child: FutureBuilder<Track>(
            future: track,
            builder: (context, snapshot) {
              if (snapshot.hasData) {
               return Column(
                    children: <Widget>[
                      new Text(snapshot.data.title),
                      //new Text(snapshot.data.body)
                    ]
              );

              } else if (snapshot.hasError) {
                return Text("${snapshot.error}");
              }
              //By default, show a loading spinner.
              return CircularProgressIndicator();
            },
          ),
        );

  }
}

Answer 1

您的问题没有具体的 Dart 或 flutter - 我检查了您的端点返回的数据(在下面粘贴和格式化)，它的结构与您的预期不符。

尤其:

数据中没有顶级Track

有一个顶级字段data包含音乐文件条目列表

每个音乐文件条目包含 track field 。这是您尝试解析的字段。

获取所有轨道数据的示例代码

var responseJson = json.decode(response.body);
var tracks = responseJson['data']
    .map((musicFileJson) => Track.fromJson(musicFileJson['track']))
    .toList()
    .cast<Track>();

源文件(供引用)

{
  "type": "result",
  "data": [
    {
      "title": "DRN1",
      "song": "JAHBOY - Karma of the Butterfly Effect",
      "track": {
        "artist": "JAHBOY",
        "title": "Karma of the Butterfly Effect",
        "album": "The Green Project",
        "royaltytrackid": 94.0000,
        "started": null,
        "id": 94,
        "length": 0,
        "playlist": {
          "id": 2,
          "title": "Standard Rotation"
        },
        "buyurl": "",
        "imageurl": "http:\/\/139.59.108.222:2197\/static\/drn1\/covers\/rsz_emb_jahboy_dreamz_f1aca1a5.jpg"
      },
      "bitrate": "128 Kbps",
      "server": "Online",
      "autodj": "Online",
      "source": "Yes",
      "offline": false,
      "summary": "<a href=\"http:\/\/139.59.108.222:2199\/tunein\/-stream\/drn1.pls\">DRN1 - JAHBOY - Karma of the Butterfly Effect<\/a>",
      "listeners": 1,
      "maxlisteners": 100,
      "reseller": 0,
      "serverstate": true,
      "sourcestate": true,
      "sourceconn": true,
      "date": "Sep 10, 2019",
      "time": "12:53 PM",
      "rawmeta": "JAHBOY - Karma of the Butterfly Effect ",
      "mountpoint": "\/stream",
      "tuneinurl": "http:\/\/139.59.108.222:8003\/stream",
      "directtuneinurl": "",
      "proxytuneinurl": "",
      "tuneinformat": "mp3",
      "webplayer": "muses",
      "servertype": "IceCast",
      "listenertotal": 1,
      "url": "http:\/\/139.59.108.222:2199\/rpc"
    }
  ]
}