未处理的异常:类型'(dynamic) => Welcome‘不是'transform’的类型'(String，dynamic) => MapEntry<dynamic，dynamic>‘的子类型
未处理的异常:类型'(dynamic) => Welcome‘不是'transform’的类型'(String，dynamic) => MapEntry<dynamic，dynamic>‘的子类型
提问于 2020-08-10 05:12:17
我正在尝试从json到dart的数据序列化。
但我没想到这个错误是无法克服的。
未处理的异常:类型'(dynamic) => Welcome‘不是'transform’的类型'(String，dynamic) => MapEntry‘的子类型
我会展示我的代码和帮助，有人可以给我答案。
这是Android Studio的错误代码源。我在这里得到了错误：
void getTracksFromApi() {
PlayListApi.getTracks().then((response) {
setState(() {
var list = json.decode(response.body);
this.trackList = list.map((track) => Welcome.fromJson(track)).toList();
var sa = list["tracks"];
print('$sa');
});
});
}也许问题出在我的模型上。我在这里使用这两个工具构建了https://app.quicktype.io和https://javiercbk.github.io/json_to_dart/模型：
import 'dart:convert';
Welcome welcomeFromJson(String str) => Welcome.fromJson(json.decode(str));
String welcomeToJson(Welcome data) => json.encode(data.toJson());
class Welcome {
Welcome({
this.tracks,
});
final Tracks tracks;
factory Welcome.fromJson(Map<String, dynamic> json) => Welcome(
tracks: json["tracks"] == null ? null : Tracks.fromJson(json["tracks"]),
);
Map<String, dynamic> toJson() => {
"tracks": tracks == null ? null : tracks.toJson(),
};
}
class Tracks {
Tracks({
this.items,
});
final List<Item> items;
factory Tracks.fromJson(Map<String, dynamic> json) => Tracks(
items: json["items"] == null
? null
: List<Item>.from(json["items"].map((x) => Item.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"items": items == null
? null
: List<dynamic>.from(items.map((x) => x.toJson())),
};
}
class Item {
Item({
this.track,
});
final Track track;
factory Item.fromJson(Map<String, dynamic> json) => Item(
track: json["track"] == null ? null : Track.fromJson(json["track"]),
);
Map<String, dynamic> toJson() => {
"track": track == null ? null : track.toJson(),
};
}
class Track {
Track({
this.album,
this.name,
this.uri,
});
final Album album;
final String name;
final String uri;
factory Track.fromJson(Map<String, dynamic> json) => Track(
album: json["album"] == null ? null : Album.fromJson(json["album"]),
name: json["name"] == null ? null : json["name"],
uri: json["uri"] == null ? null : json["uri"],
);
Map<String, dynamic> toJson() => {
"album": album == null ? null : album.toJson(),
"name": name == null ? null : name,
"uri": uri == null ? null : uri,
};
}
class Album {
Album({
this.artists,
this.images,
});
final List<Artist> artists;
final List<Image> images;
factory Album.fromJson(Map<String, dynamic> json) => Album(
artists: json["artists"] == null
? null
: List<Artist>.from(json["artists"].map((x) => Artist.fromJson(x))),
images: json["images"] == null
? null
: List<Image>.from(json["images"].map((x) => Image.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"artists": artists == null
? null
: List<dynamic>.from(artists.map((x) => x.toJson())),
"images": images == null
? null
: List<dynamic>.from(images.map((x) => x.toJson())),
};
}
class Artist {
Artist({
this.externalUrls,
this.href,
this.id,
this.name,
this.type,
this.uri,
});
final ExternalUrls externalUrls;
final String href;
final String id;
final String name;
final String type;
final String uri;
factory Artist.fromJson(Map<String, dynamic> json) => Artist(
externalUrls: json["external_urls"] == null
? null
: ExternalUrls.fromJson(json["external_urls"]),
href: json["href"] == null ? null : json["href"],
id: json["id"] == null ? null : json["id"],
name: json["name"] == null ? null : json["name"],
type: json["type"] == null ? null : json["type"],
uri: json["uri"] == null ? null : json["uri"],
);
Map<String, dynamic> toJson() => {
"external_urls": externalUrls == null ? null : externalUrls.toJson(),
"href": href == null ? null : href,
"id": id == null ? null : id,
"name": name == null ? null : name,
"type": type == null ? null : type,
"uri": uri == null ? null : uri,
};
}
class ExternalUrls {
ExternalUrls({
this.spotify,
});
final String spotify;
factory ExternalUrls.fromJson(Map<String, dynamic> json) => ExternalUrls(
spotify: json["spotify"] == null ? null : json["spotify"],
);
Map<String, dynamic> toJson() => {
"spotify": spotify == null ? null : spotify,
};
}
class Image {
Image({
this.height,
this.url,
this.width,
});
final int height;
final String url;
final int width;
factory Image.fromJson(Map<String, dynamic> json) => Image(
height: json["height"] == null ? null : json["height"],
url: json["url"] == null ? null : json["url"],
width: json["width"] == null ? null : json["width"],
);
Map<String, dynamic> toJson() => {
"height": height == null ? null : height,
"url": url == null ? null : url,
"width": width == null ? null : width,
};
}我还添加了json数据，以查看错误所在：
{
"tracks": {
"items": [
{
"track": {
"album": {
"artists": [
{
"external_urls": {
"spotify": "https://open.spotify.com/artist/3vJJGsSAF5zQegZo5sJEh6"
},
"href": "https://api.spotify.com/v1/artists/3vJJGsSAF5zQegZo5sJEh6",
"id": "3vJJGsSAF5zQegZo5sJEh6",
"name": "Can Bonomo",
"type": "artist",
"uri": "spotify:artist:3vJJGsSAF5zQegZo5sJEh6"
}
],
"images": [
{
"height": 640,
"url": "https://i.scdn.co/image/ab67616d0000b273438198f2165a7954bcfd9b81",
"width": 640
},
{
"height": 300,
"url": "https://i.scdn.co/image/ab67616d00001e02438198f2165a7954bcfd9b81",
"width": 300
},
{
"height": 64,
"url": "https://i.scdn.co/image/ab67616d00004851438198f2165a7954bcfd9b81",
"width": 64
}
]
},
"name": "Güneş",
"uri": "spotify:track:4LmA7eKmD04MBZ4kHWXbLz"
}
},
{
"track": {
"album": {
"artists": [
{
"external_urls": {
"spotify": "https://open.spotify.com/artist/3vJJGsSAF5zQegZo5sJEh6"
},
"href": "https://api.spotify.com/v1/artists/3vJJGsSAF5zQegZo5sJEh6",
"id": "3vJJGsSAF5zQegZo5sJEh6",
"name": "Can Bonomo",
"type": "artist",
"uri": "spotify:artist:3vJJGsSAF5zQegZo5sJEh6"
}
],
"images": [
{
"height": 640,
"url": "https://i.scdn.co/image/ab67616d0000b27380cb1ec0ca1c857dfccecfde",
"width": 640
},
{
"height": 300,
"url": "https://i.scdn.co/image/ab67616d00001e0280cb1ec0ca1c857dfccecfde",
"width": 300
},
{
"height": 64,
"url": "https://i.scdn.co/image/ab67616d0000485180cb1ec0ca1c857dfccecfde",
"width": 64
}
]
},
"name": "Dem",
"uri": "spotify:track:2aUycmP66tY4wr3zt1sGc0"
}
},
{
"track": {
"album": {
"artists": [
{
"external_urls": {
"spotify": "https://open.spotify.com/artist/3vJJGsSAF5zQegZo5sJEh6"
},
"href": "https://api.spotify.com/v1/artists/3vJJGsSAF5zQegZo5sJEh6",
"id": "3vJJGsSAF5zQegZo5sJEh6",
"name": "Can Bonomo",
"type": "artist",
"uri": "spotify:artist:3vJJGsSAF5zQegZo5sJEh6"
}
],
"images": [
{
"height": 640,
"url": "https://i.scdn.co/image/ab67616d0000b27380cb1ec0ca1c857dfccecfde",
"width": 640
},
{
"height": 300,
"url": "https://i.scdn.co/image/ab67616d00001e0280cb1ec0ca1c857dfccecfde",
"width": 300
},
{
"height": 64,
"url": "https://i.scdn.co/image/ab67616d0000485180cb1ec0ca1c857dfccecfde",
"width": 64
}
]
},
"name": "Tastamam",
"uri": "spotify:track:3L8SvgfqK9Xb26rV4kq5Xt"
}
},
{
"track": {
"album": {
"artists": [
{
"external_urls": {
"spotify": "https://open.spotify.com/artist/3vJJGsSAF5zQegZo5sJEh6"
},
"href": "https://api.spotify.com/v1/artists/3vJJGsSAF5zQegZo5sJEh6",
"id": "3vJJGsSAF5zQegZo5sJEh6",
"name": "Can Bonomo",
"type": "artist",
"uri": "spotify:artist:3vJJGsSAF5zQegZo5sJEh6"
}
],
"images": [
{
"height": 640,
"url": "https://i.scdn.co/image/ab67616d0000b27380cb1ec0ca1c857dfccecfde",
"width": 640
},
{
"height": 300,
"url": "https://i.scdn.co/image/ab67616d00001e0280cb1ec0ca1c857dfccecfde",
"width": 300
},
{
"height": 64,
"url": "https://i.scdn.co/image/ab67616d0000485180cb1ec0ca1c857dfccecfde",
"width": 64
}
]
},
"name": "Hikayem Bitmedi",
"uri": "spotify:track:5YUjVwnxQeYJAxq6bElGWU"
}
},
{
"track": {
"album": {
"artists": [
{
"external_urls": {
"spotify": "https://open.spotify.com/artist/3vJJGsSAF5zQegZo5sJEh6"
},
"href": "https://api.spotify.com/v1/artists/3vJJGsSAF5zQegZo5sJEh6",
"id": "3vJJGsSAF5zQegZo5sJEh6",
"name": "Can Bonomo",
"type": "artist",
"uri": "spotify:artist:3vJJGsSAF5zQegZo5sJEh6"
}
],
"images": [
{
"height": 640,
"url": "https://i.scdn.co/image/ab67616d0000b27380cb1ec0ca1c857dfccecfde",
"width": 640
},
{
"height": 300,
"url": "https://i.scdn.co/image/ab67616d00001e0280cb1ec0ca1c857dfccecfde",
"width": 300
},
{
"height": 64,
"url": "https://i.scdn.co/image/ab67616d0000485180cb1ec0ca1c857dfccecfde",
"width": 64
}
]
},
"name": "Her Kız Başka",
"uri": "spotify:track:1kbHEESbmALWauoUtYPNAr"
}
},
{
"track": {
"album": {
"artists": [
{
"external_urls": {
"spotify": "https://open.spotify.com/artist/3vJJGsSAF5zQegZo5sJEh6"
},
"href": "https://api.spotify.com/v1/artists/3vJJGsSAF5zQegZo5sJEh6",
"id": "3vJJGsSAF5zQegZo5sJEh6",
"name": "Can Bonomo",
"type": "artist",
"uri": "spotify:artist:3vJJGsSAF5zQegZo5sJEh6"
}
],
"images": [
{
"height": 640,
"url": "https://i.scdn.co/image/ab67616d0000b27380cb1ec0ca1c857dfccecfde",
"width": 640
},
{
"height": 300,
"url": "https://i.scdn.co/image/ab67616d00001e0280cb1ec0ca1c857dfccecfde",
"width": 300
},
{
"height": 64,
"url": "https://i.scdn.co/image/ab67616d0000485180cb1ec0ca1c857dfccecfde",
"width": 64
}
]
},
"name": "Senin Olmadan Ölemem",
"uri": "spotify:track:5z1bH63TwXLslyDcDZKmqR"
}
},
{
"track": {
"album": {
"artists": [
{
"external_urls": {
"spotify": "https://open.spotify.com/artist/3vJJGsSAF5zQegZo5sJEh6"
},
"href": "https://api.spotify.com/v1/artists/3vJJGsSAF5zQegZo5sJEh6",
"id": "3vJJGsSAF5zQegZo5sJEh6",
"name": "Can Bonomo",
"type": "artist",
"uri": "spotify:artist:3vJJGsSAF5zQegZo5sJEh6"
}
],
"images": [
{
"height": 640,
"url": "https://i.scdn.co/image/ab67616d0000b27380cb1ec0ca1c857dfccecfde",
"width": 640
},
{
"height": 300,
"url": "https://i.scdn.co/image/ab67616d00001e0280cb1ec0ca1c857dfccecfde",
"width": 300
},
{
"height": 64,
"url": "https://i.scdn.co/image/ab67616d0000485180cb1ec0ca1c857dfccecfde",
"width": 64
}
]
},
"name": "Bir Çocuk Yaralı",
"uri": "spotify:track:6Czfr9RR7OpklOBHHcu658"
}
},
{
"track": {
"album": {
"artists": [
{
"external_urls": {
"spotify": "https://open.spotify.com/artist/3vJJGsSAF5zQegZo5sJEh6"
},
"href": "https://api.spotify.com/v1/artists/3vJJGsSAF5zQegZo5sJEh6",
"id": "3vJJGsSAF5zQegZo5sJEh6",
"name": "Can Bonomo",
"type": "artist",
"uri": "spotify:artist:3vJJGsSAF5zQegZo5sJEh6"
}
],
"images": [
{
"height": 640,
"url": "https://i.scdn.co/image/ab67616d0000b27380cb1ec0ca1c857dfccecfde",
"width": 640
},
{
"height": 300,
"url": "https://i.scdn.co/image/ab67616d00001e0280cb1ec0ca1c857dfccecfde",
"width": 300
},
{
"height": 64,
"url": "https://i.scdn.co/image/ab67616d0000485180cb1ec0ca1c857dfccecfde",
"width": 64
}
]
},
"name": "Kaçak",
"uri": "spotify:track:2R7w5iT5H43KmANEryoAn8"
}
},
{
"track": {
"album": {
"artists": [
{
"external_urls": {
"spotify": "https://open.spotify.com/artist/3vJJGsSAF5zQegZo5sJEh6"
},
"href": "https://api.spotify.com/v1/artists/3vJJGsSAF5zQegZo5sJEh6",
"id": "3vJJGsSAF5zQegZo5sJEh6",
"name": "Can Bonomo",
"type": "artist",
"uri": "spotify:artist:3vJJGsSAF5zQegZo5sJEh6"
}
],
"images": [
{
"height": 640,
"url": "https://i.scdn.co/image/ab67616d0000b27380cb1ec0ca1c857dfccecfde",
"width": 640
},
{
"height": 300,
"url": "https://i.scdn.co/image/ab67616d00001e0280cb1ec0ca1c857dfccecfde",
"width": 300
},
{
"height": 64,
"url": "https://i.scdn.co/image/ab67616d0000485180cb1ec0ca1c857dfccecfde",
"width": 64
}
]
},
"name": "Resmini Görünce",
"uri": "spotify:track:3lBfCNZ72P6ruxCkqV9lEu"
}
},
{
"track": {
"album": {
"artists": [
{
"external_urls": {
"spotify": "https://open.spotify.com/artist/3vJJGsSAF5zQegZo5sJEh6"
},
"href": "https://api.spotify.com/v1/artists/3vJJGsSAF5zQegZo5sJEh6",
"id": "3vJJGsSAF5zQegZo5sJEh6",
"name": "Can Bonomo",
"type": "artist",
"uri": "spotify:artist:3vJJGsSAF5zQegZo5sJEh6"
}
],
"images": [
{
"height": 640,
"url": "https://i.scdn.co/image/ab67616d0000b27380cb1ec0ca1c857dfccecfde",
"width": 640
},
{
"height": 300,
"url": "https://i.scdn.co/image/ab67616d00001e0280cb1ec0ca1c857dfccecfde",
"width": 300
},
{
"height": 64,
"url": "https://i.scdn.co/image/ab67616d0000485180cb1ec0ca1c857dfccecfde",
"width": 64
}
]
},
"name": "Bulunmam Gerek",
"uri": "spotify:track:6lTu9NoZWUqgh7ZxiAkU1O"
}
},
{
"track": {
"album": {
"artists": [
{
"external_urls": {
"spotify": "https://open.spotify.com/artist/3vJJGsSAF5zQegZo5sJEh6"
},
"href": "https://api.spotify.com/v1/artists/3vJJGsSAF5zQegZo5sJEh6",
"id": "3vJJGsSAF5zQegZo5sJEh6",
"name": "Can Bonomo",
"type": "artist",
"uri": "spotify:artist:3vJJGsSAF5zQegZo5sJEh6"
}
],
"images": [
{
"height": 640,
"url": "https://i.scdn.co/image/ab67616d0000b27380cb1ec0ca1c857dfccecfde",
"width": 640
},
{
"height": 300,
"url": "https://i.scdn.co/image/ab67616d00001e0280cb1ec0ca1c857dfccecfde",
"width": 300
},
{
"height": 64,
"url": "https://i.scdn.co/image/ab67616d0000485180cb1ec0ca1c857dfccecfde",
"width": 64
}
]
},
"name": "Bahr-i Hazer",
"uri": "spotify:track:0vxMon7God4sDfGZS4ImmC"
}
}
]
}
}最后是我的api请求。我检查了一下答案是否正确。
static Future getTracks() async {
var res = await http.get(
"https://api.spotify.com/v1/playlists/6f3gB3WYLwTzAzUX3PdOmr?fields=tracks.items(track(name%2Curi%2Calbum(images%2Cartists)))",
headers: headers);
if (res.statusCode == 200) {
return res;
} else {
throw Exception(res.statusCode);
}
}回答 1
Stack Overflow用户
回答已采纳
发布于 2020-08-10 10:43:55
var list并不像您的代码所显示的那样是一个List。
该错误和您的示例JSON表明它是一个Map。Map类的map方法采用与Lists的map方法不同的函数参数。
已经创建了JSON模型，以便直接处理解析后的JSON，而无需进行任何映射，然后再将其传递给fromJson构造函数。
只需删除map函数调用：
void getTracksFromApi() {
PlayListApi.getTracks().then((response) {
setState(() {
var map = json.decode(response.body);
Welcome modelObject = Welcome.fromJson(map);
//this.trackList = ;This has to be modified to suit your particular needs
});
});
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/63331381
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