我正在处理项目，并且在发布请求时遇到错误，当我使用邮递员时，它工作正常，但是当我使用Flutter时，它给了我type 'List<Map<String, String>>' is not a subtype of type 'String' in type cast异常提示
邮递员的身体和反应： （https://i.imgur.com/HS5Y6CA.png）
Flutter代码：
try {
http.Response response = await http.post(Uri.parse(url),
headers: {
"Accept": "application/json",
'authorization' : 'Bearer ${tokenValue}',
},
body: {
"date": "2019-12-30",
"studentId": "1",
"amount": "10",
"numberOfItems": "2",
"mqsfId": "1",
"items": [{
"itemCount": "1",
"productId": "1",
"productName": "Apple juice",
"productPrice": "8"
}, {
"itemCount": "1",
"productId": "2",
"productName": "Sandwish",
"productPrice": "2"
}]
});
resBody = json.decode(response.body);
if (response.statusCode == 201) {
// Some Actions
} else {
// Some Actions
}
} catch(e) {
print(e);
}
此代码返回我异常消息：type 'List<Map<String, String>>' is not a sub type of type 'String' in type cast
当我将嵌套列表转换为String时：
"items":[{
"itemCount": "1",
"productId": "1",
"productName": "Apple juice",
"productPrice": "8"
}, {
"itemCount": "1",
"productId": "2",
"productName": "Sandwish",
"productPrice": "2"
}].toString()
它发送请求并以StatusCode 500返回服务器错误，但是当我检查数据库时记录了订单，但是nested array is empty !!
记录的数据示例（服务器错误请求的输出）：
date: 2019-12-30,
studentId: 1,
amount: 10,
numberOfItems: 2,
mqsfId: 1,
items:[]
// item shouldn't be empty
答案 0 :(得分：0)
您可以使用以下
var response = await http.post(url, body: payload);
代码片段以使用json字符串或对象创建有效负载
payload = payloadFromJson(jsonString);
print('item 0 product name ${payload.items[0].productName}');
Item item1 = Item(itemCount: "1", productName: "abc");
Item item2 = Item(itemCount: "2", productName: "def");
List<Item> itemList = [];
itemList.add(item1);
itemList.add(item2);
Payload payload1 = Payload(date: DateTime.parse("2019-12-30"), items: itemList );
print('item 0 product name ${payload1.items[0].productName}');
相关课程
// To parse this JSON data, do
//
// final payload = payloadFromJson(jsonString);
import 'dart:convert';
Payload payloadFromJson(String str) => Payload.fromJson(json.decode(str));
String payloadToJson(Payload data) => json.encode(data.toJson());
class Payload {
DateTime date;
String studentId;
String amount;
String numberOfItems;
String mqsfId;
List<Item> items;
Payload({
this.date,
this.studentId,
this.amount,
this.numberOfItems,
this.mqsfId,
this.items,
});
factory Payload.fromJson(Map<String, dynamic> json) => Payload(
date: DateTime.parse(json["date"]),
studentId: json["studentId"],
amount: json["amount"],
numberOfItems: json["numberOfItems"],
mqsfId: json["mqsfId"],
items: List<Item>.from(json["items"].map((x) => Item.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"date": "${date.year.toString().padLeft(4, '0')}-${date.month.toString().padLeft(2, '0')}-${date.day.toString().padLeft(2, '0')}",
"studentId": studentId,
"amount": amount,
"numberOfItems": numberOfItems,
"mqsfId": mqsfId,
"items": List<dynamic>.from(items.map((x) => x.toJson())),
};
}
class Item {
String itemCount;
String productId;
String productName;
String productPrice;
Item({
this.itemCount,
this.productId,
this.productName,
this.productPrice,
});
factory Item.fromJson(Map<String, dynamic> json) => Item(
itemCount: json["itemCount"],
productId: json["productId"],
productName: json["productName"],
productPrice: json["productPrice"],
);
Map<String, dynamic> toJson() => {
"itemCount": itemCount,
"productId": productId,
"productName": productName,
"productPrice": productPrice,
};
}
完整代码
import 'package:flutter/material.dart';
// To parse this JSON data, do
//
// final payload = payloadFromJson(jsonString);
import 'dart:convert';
Payload payloadFromJson(String str) => Payload.fromJson(json.decode(str));
String payloadToJson(Payload data) => json.encode(data.toJson());
class Payload {
DateTime date;
String studentId;
String amount;
String numberOfItems;
String mqsfId;
List<Item> items;
Payload({
this.date,
this.studentId,
this.amount,
this.numberOfItems,
this.mqsfId,
this.items,
});
factory Payload.fromJson(Map<String, dynamic> json) => Payload(
date: DateTime.parse(json["date"]),
studentId: json["studentId"],
amount: json["amount"],
numberOfItems: json["numberOfItems"],
mqsfId: json["mqsfId"],
items: List<Item>.from(json["items"].map((x) => Item.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"date": "${date.year.toString().padLeft(4, '0')}-${date.month.toString().padLeft(2, '0')}-${date.day.toString().padLeft(2, '0')}",
"studentId": studentId,
"amount": amount,
"numberOfItems": numberOfItems,
"mqsfId": mqsfId,
"items": List<dynamic>.from(items.map((x) => x.toJson())),
};
}
class Item {
String itemCount;
String productId;
String productName;
String productPrice;
Item({
this.itemCount,
this.productId,
this.productName,
this.productPrice,
});
factory Item.fromJson(Map<String, dynamic> json) => Item(
itemCount: json["itemCount"],
productId: json["productId"],
productName: json["productName"],
productPrice: json["productPrice"],
);
Map<String, dynamic> toJson() => {
"itemCount": itemCount,
"productId": productId,
"productName": productName,
"productPrice": productPrice,
};
}
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
// This is the theme of your application.
//
// Try running your application with "flutter run". You'll see the
// application has a blue toolbar. Then, without quitting the app, try
// changing the primarySwatch below to Colors.green and then invoke
// "hot reload" (press "r" in the console where you ran "flutter run",
// or simply save your changes to "hot reload" in a Flutter IDE).
// Notice that the counter didn't reset back to zero; the application
// is not restarted.
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
// This widget is the home page of your application. It is stateful, meaning
// that it has a State object (defined below) that contains fields that affect
// how it looks.
// This class is the configuration for the state. It holds the values (in this
// case the title) provided by the parent (in this case the App widget) and
// used by the build method of the State. Fields in a Widget subclass are
// always marked "final".
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
String jsonString = '''
{
"date": "2019-12-30",
"studentId": "1",
"amount": "10",
"numberOfItems": "2",
"mqsfId": "1",
"items":[
{
"itemCount": "1",
"productId": "1",
"productName": "Apple juice",
"productPrice": "8"
},
{
"itemCount": "1",
"productId": "2",
"productName": "Sandwish",
"productPrice": "2"
}
]
}
''';
Payload payload;
void _incrementCounter() {
payload = payloadFromJson(jsonString);
print('item 0 product name ${payload.items[0].productName}');
Item item1 = Item(itemCount: "1", productName: "abc");
Item item2 = Item(itemCount: "2", productName: "def");
List<Item> itemList = [];
itemList.add(item1);
itemList.add(item2);
Payload payload1 = Payload(date: DateTime.parse("2019-12-30"), items: itemList );
print('item 0 product name ${payload1.items[0].productName}');
setState(() {
// This call to setState tells the Flutter framework that something has
// changed in this State, which causes it to rerun the build method below
// so that the display can reflect the updated values. If we changed
// _counter without calling setState(), then the build method would not be
// called again, and so nothing would appear to happen.
_counter++;
});
}
@override
Widget build(BuildContext context) {
// This method is rerun every time setState is called, for instance as done
// by the _incrementCounter method above.
//
// The Flutter framework has been optimized to make rerunning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
return Scaffold(
appBar: AppBar(
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: Text(widget.title),
),
body: Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(
// Column is also a layout widget. It takes a list of children and
// arranges them vertically. By default, it sizes itself to fit its
// children horizontally, and tries to be as tall as its parent.
//
// Invoke "debug painting" (press "p" in the console, choose the
// "Toggle Debug Paint" action from the Flutter Inspector in Android
// Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
// to see the wireframe for each widget.
//
// Column has various properties to control how it sizes itself and
// how it positions its children. Here we use mainAxisAlignment to
// center the children vertically; the main axis here is the vertical
// axis because Columns are vertical (the cross axis would be
// horizontal).
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
输出
I/flutter (32293): item 0 product name Apple juice
I/flutter (32293): item 0 product name abc
答案 1 :(得分：0)
直到我发现这个from the docs为止，这令人困惑：
body sets the body of the request. It can be a String, a List<int> or a Map<String, String>.
仅将字段的值转换为String显然会阻止其解析。
好，让我们尝试一下（基于here）：
http.Response response = await http.post(Uri.parse(url),
headers: {
'Content-type' : 'application/json',
"Accept": "application/json",
'authorization' : 'Bearer ${tokenValue}',
},
body: json.encode({
"date": "2019-12-30",
"studentId": "1",
"amount": "10",
"numberOfItems": "2",
"mqsfId": "1",
"items":[
{
"itemCount": "1",
"productId": "1",
"productName": "Apple juice",
"productPrice": "8"
},
{
"itemCount": "1",
"productId": "2",
"productName": "Sandwish",
"productPrice": "2"
}
]
})
);