颤振：将 json 实现为列表返回一个空列表
Posted
技术标签:
【中文标题】颤振：将 json 实现为列表返回一个空列表【英文标题】：flutter : implementing json as list returns a null list 【发布时间】：2021-01-24 03:13:13 【问题描述】：你好，我正在制作一个新的颤振应用程序，我是颤振新手，我使用的是 mysql 数据库，我得到的响应是 json 。 这是我格式化的 json 响应：
JsonResponse
"folders":[
"id":2107,
"name":"Labs ",
"img":null,
"haschild":1,
"parentid":1955,
"createdate":"2019-09-30 03:00:39",
"inarchive":0,
"active":1
,
"id":2108,
"name":"L1",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-09-30 03:00:45",
"inarchive":0,
"active":1
,
"id":2130,
"name":"L2",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-10-02
02:39:11",
"inarchive":0,
"active":1
,
"id":2175,
"name":"L3",
"img":null,
"haschild":1,
"parentid":1955,
"createdate":"2019-10-07 03:43:15",
"inarchive":0,
"active":1
,
"id":2202,
"name":"L4",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-10-09 02:08:10",
"inarchive":0,
"active":1
,
"id":2227,
"name":"\u0645\u0631\u0627\u062c\u0639\u0627\u062a
",
"img":null,
"haschild":1,
"parentid":1955,
"createdate":"2019-10-11 05:15:43",
"inarchive":0,
"active":1
,
"id":2242,
"name":"L5",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-10-14 03:45:24",
"inarchive":0,
"active":1
,
"id":2257,
"name":"L6",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-10-16
06:23:41",
"inarchive":0,
"active":1
,
"id":2269,
"name":"L7",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-10-21 03:39:12",
"inarchive":0,
"active":1
,
"id":2309,
"name":"L8",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-10-23 05:14:48",
"inarchive":0,
"active":1
,
"id":2310,
"name":"L8",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-10-23
05:14:51",
"inarchive":0,
"active":1
,
"id":2346,
"name":"L9",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-10-28 04:22:24",
"inarchive":0,
"active":1
,
"id":2370,
"name":"L10",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-10-30 03:02:00",
"inarchive":0,
"active":1
,
"id":2446,
"name":"L11",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-11-12
06:28:13",
"inarchive":0,
"active":1
,
"id":2462,
"name":"\u062a\u0628\u064a\u0636\u0627\u062a",
"img":null,
"haschild":1,
"parentid":1955,
"createdate":"2019-11-13 08:39:00",
"inarchive":0,
"active":1
,
"id":2464,
"name":"L12",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-11-13
08:40:55",
"inarchive":0,
"active":1
,
"id":2488,
"name":"L13",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-11-18 06:09:11",
"inarchive":0,
"active":1
,
"id":2490,
"name":"L14",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-11-18 06:38:59",
"inarchive":0,
"active":1
,
"id":2491,
"name":"L15",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-11-18
06:45:57",
"inarchive":0,
"active":1
,
"id":2497,
"name":"\u062a\u0644\u062e\u064a\u0635\u0627\u062a",
"img":null,
"haschild":1,
"parentid":1955,
"createdate":"2019-11-19 04:24:49",
"inarchive":0,
"active":1
,
"id":2509,
"name":"L16",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-11-20
09:56:04",
"inarchive":0,
"active":1
,
"id":2522,
"name":"L17",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-11-25 06:38:27",
"inarchive":0,
"active":1
,
"id":2542,
"name":"L18",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-11-27 12:19:12",
"inarchive":0,
"active":1
,
"id":2552,
"name":"Protein
Lab",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-11-27 16:32:27",
"inarchive":0,
"active":1
,
"id":2562,
"name":"Chromatography ",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-11-30 15:24:24",
"inarchive":0,
"active":1
,
"id":2576,
"name":"L19",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-12-02
02:05:29",
"inarchive":0,
"active":1
,
"id":2580,
"name":"L20",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-12-02 08:23:48",
"inarchive":0,
"active":1
,
"id":2592,
"name":"21",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-12-03 06:27:24",
"inarchive":0,
"active":1
,
"id":2600,
"name":"L22",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-12-04
06:22:46",
"inarchive":0,
"active":1
,
"id":2614,
"name":"L23",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-12-04 10:03:00",
"inarchive":0,
"active":1
,
"id":2640,
"name":"L24",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-12-08 06:53:11",
"inarchive":0,
"active":1
,
"id":2644,
"name":"L25",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-12-09
05:33:07",
"inarchive":0,
"active":1
,
"id":2649,
"name":"L26",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-12-09 07:58:42",
"inarchive":0,
"active":1
,
"id":2711,
"name":"\u0623\u0633\u0626\u0644\u0629",
"img":null,
"haschild":0,
"parentid":1955,
"createdate":"2019-12-19
05:18:11",
"inarchive":0,
"active":1
],
"files":[
"id":4542,
"name":"Ch2-part1.m4a 27.52MB",
"img":null,
"uploader":"Aws",
"url":"http:\/\/msc-mu.com\/..\/uploaded\/031020190Ch2-part1.m4a",
"createdate":"2019-10-03 09:53:39",
"approved":1,
"active":1
]
每当我尝试实现文件夹和文件列表时，它都会说列表中没有任何内容，并且它为空 这是我的代码： fellow.dart
class SecondScreen extends StatefulWidget
final YearsMain value;
SecondScreen(Key key, this.value) : super(key: key);
@override
_SecondScreenState createState() => _SecondScreenState();
class _SecondScreenState extends State<SecondScreen>
Future<List<Folders>> getData() async
List<Folders> list;
String link =
"http://msc-mu.com/api_verfication.php";
var res = await http.post(link,body:
'flag':'selectfellowsubjects',
'year':widget.value.id
);
print(res.body);
if (res.statusCode == 200)
var data = json.decode(res.body);
var rest = data["folders"] as List;
print(rest);
list = rest.map<Folders>((json) => Folders.fromJson(json)).toList();
print("List Size: $list.length");
return list;
Widget listViewWidget(List<Folders> article)
return Container(
child: ListView.builder(
itemCount: 20,
padding: const EdgeInsets.all(2.0),
itemBuilder: (context, position)
return Card(
child: ListTile(
title: Text(
'$article[position].name',
style: TextStyle(
fontSize: 18.0,
color: Colors.black,
fontWeight: FontWeight.bold),
),
onTap: () => _onTapItem(context, article[position]),
),
);
),
);
void _onTapItem(BuildContext context, Folders folders)
Navigator.of(context).push(MaterialPageRoute(
builder: (BuildContext context) => DownloadPage()));
@override
void initState()
// TODO: implement initState
super.initState();
print(widget.value.id);
@override
Widget build(BuildContext context)
return Scaffold(
body: Center(
child: new FutureBuilder<List<Folders>>(
future: getData(),
builder: (context, snapshot)
if (snapshot.hasData)
List fellow = snapshot.data;
return listViewWidget(fellow);
else if (snapshot.hasError)
return Text('$snapshot.error');
return CircularProgressIndicator();
,
),
),
);
这是输出：
I/flutter (21630): "folders":[],"files":[]
I/flutter (21630): []
I/flutter (21630): List Size: 0
有什么帮助吗？
【问题讨论】：
嗨！你可以试试 data["folders"].forEach((v) list .add(Folders.fromJson(v)); ); ` Future> getData() async ListFuture<List<Folders>> getData() async
List<Folders> list= <Folders>[];
String link = "msc-mu.com/api_verfication.php";
try
var res = await http.post(link,
body: 'flag': 'selectfellowsubjects', 'year': widget.value.id);
print(res.body);
if (res.statusCode == 200)
var data = json.decode(res.body);
var rest = data["folders"].forEach((v)
list.add(Folders.fromJson(v));
);
print(rest);
return list;
catch (e)
debugPrint('$e');
【讨论】：
type 不是 type class FilesAndFoldersModel
List<Folders> folders;
List<Files> files;
FilesAndFoldersModel(this.folders, this.files);
FilesAndFoldersModel.fromJson(Map<String, dynamic> json)
if (json['folders'] != null)
folders = new List<Folders>();
json['folders'].forEach((v)
folders.add(new Folders.fromJson(v));
);
if (json['files'] != null)
files = new List<Files>();
json['files'].forEach((v)
files.add(new Files.fromJson(v));
);
Map<String, dynamic> toJson()
final Map<String, dynamic> data = new Map<String, dynamic>();
if (this.folders != null)
data['folders'] = this.folders.map((v) => v.toJson()).toList();
if (this.files != null)
data['files'] = this.files.map((v) => v.toJson()).toList();
return data;
class Folders
int id;
String name;
Null img;
int haschild;
int parentid;
String createdate;
int inarchive;
int active;
Folders(
this.id,
this.name,
this.img,
this.haschild,
this.parentid,
this.createdate,
this.inarchive,
this.active);
Folders.fromJson(Map<String, dynamic> json)
id = json['id'];
name = json['name'];
img = json['img'];
haschild = json['haschild'];
parentid = json['parentid'];
createdate = json['createdate'];
inarchive = json['inarchive'];
active = json['active'];
Map<String, dynamic> toJson()
final Map<String, dynamic> data = new Map<String, dynamic>();
data['id'] = this.id;
data['name'] = this.name;
data['img'] = this.img;
data['haschild'] = this.haschild;
data['parentid'] = this.parentid;
data['createdate'] = this.createdate;
data['inarchive'] = this.inarchive;
data['active'] = this.active;
return data;
class Files
int id;
String name;
Null img;
String uploader;
String url;
String createdate;
int approved;
int active;
Files(
this.id,
this.name,
this.img,
this.uploader,
this.url,
this.createdate,
this.approved,
this.active);
Files.fromJson(Map<String, dynamic> json)
id = json['id'];
name = json['name'];
img = json['img'];
uploader = json['uploader'];
url = json['url'];
createdate = json['createdate'];
approved = json['approved'];
active = json['active'];
Map<String, dynamic> toJson()
final Map<String, dynamic> data = new Map<String, dynamic>();
data['id'] = this.id;
data['name'] = this.name;
data['img'] = this.img;
data['uploader'] = this.uploader;
data['url'] = this.url;
data['createdate'] = this.createdate;
data['approved'] = this.approved;
data['active'] = this.active;
return data;
在制作完这样的模型后，你应该做空检查来检查每个值是否有一个值。
【讨论】：
你能告诉我下一步该怎么做吗？或更新您的答案以在 ui 及其功能中实现它？ 您现在可以通过创建模型的实例来访问模型。模型制作完成后，我建议您调用模型并对其进行空检查。以上是关于颤振：将 json 实现为列表返回一个空列表的主要内容，如果未能解决你的问题，请参考以下文章
Flutter / Dart / Firebase - 流返回空列表