Flutter开发-网络请求与JSON转换

码客说

发布于 2020-05-14 16:49:06

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发布于 2020-05-14 16:49:06

文章被收录于专栏：码客

网络请求

添加依赖

dependencies:
  dio: ^3.0.9

导入并创建dio实例：

import 'package:dio/dio.dart';
Dio dio =  Dio();

示例

发起 GET 请求 :

Response response;
response=await dio.get("/test?id=12&name=wendu")
print(response.data.toString());

对于GET请求我们可以将query参数通过对象来传递，上面的代码等同于：

response=await dio.get("/test",queryParameters:{"id":12,"name":"wendu"})
print(response);

发起一个 POST 请求:

response=await dio.post("/test",data:{"id":12,"name":"wendu"})

发起多个并发请求:

response= await Future.wait([dio.post("/info"),dio.get("/token")]);

下载文件:

response=await dio.download("https://www.google.com/",_savePath);

发送 FormData:

FormData formData = new FormData.from({
   "name": "wendux",
   "age": 25,
});
response = await dio.post("/info", data: formData)

如果发送的数据是FormData，则dio会将请求header的contentType设为“multipart/form-data”。

通过FormData上传多个文件:

FormData formData = new FormData.from({
   "name": "wendux",
   "age": 25,
   "file1": new UploadFileInfo(new File("./upload.txt"), "upload1.txt"),
   "file2": new UploadFileInfo(new File("./upload.txt"), "upload2.txt"),
     // 支持文件数组上传
   "files": [
      new UploadFileInfo(new File("./example/upload.txt"), "upload.txt"),
      new UploadFileInfo(new File("./example/upload.txt"), "upload.txt")
    ]
});
response = await dio.post("/info", data: formData)

值得一提的是，dio内部仍然使用HttpClient发起的请求，所以代理、请求认证、证书校验等和HttpClient是相同的，我们可以在onHttpClientCreate回调中设置，例如：

(dio.httpClientAdapter as DefaultHttpClientAdapter).onHttpClientCreate = (client) {
    //设置代理 
    client.findProxy = (uri) {
      return "PROXY 192.168.1.2:8888";
    };
    //校验证书
    httpClient.badCertificateCallback=(X509Certificate cert, String host, int port){
      if(cert.pem==PEM){
      return true; //证书一致，则允许发送数据
     }
     return false;
    };   
  };

注意，onHttpClientCreate会在当前dio实例内部需要创建HttpClient时调用，所以通过此回调配置HttpClient会对整个dio实例生效，如果你想针对某个应用请求单独的代理或证书校验策略，可以创建一个新的dio实例即可。

JSON解析

读取本地JSON文件

比如要读取项目根目录下的assets/person.json

首先要在 pubspec.yaml 中做如下配置：

flutter:
    uses-material-design:  true
    # 资源文件配置
    assets:
        -  assets/person.json

导入如下几个依赖库：

// 使用该库中的 rootBundle 对象来读取 perosn.json 文件
import 'package:flutter/services.dart';  
// json
import 'dart:convert';  
// 异步 Future
import 'dart:async';

实体类

class Person {
  String name;
  int age;
  double height;

  Person({this.name, this.age, this.height});

  factory Person.fromJson(Map<String, dynamic> json) {
    return Person(name: json['name'], age: json['age'], height: json['height']);
  }
}

读取转换

import 'package:flutter/services.dart';
import 'dart:convert';
import 'dart:async';
import '../models/person.dart';

// 读取 assets 文件夹中的 person.json 文件
Future<String> _loadPersonJson() async {
  return await rootBundle.loadString('assets/person.json');
}

// 将 json 字符串解析为 Person 对象
Future<Person> decodePerson() async {
  // 获取本地的 json 字符串
  String personJson = await _loadPersonJson();

  // 解析 json 字符串，返回的是 Map<String, dynamic> 类型
  final jsonMap = json.decode(personJson);

  print('jsonMap runType is ${jsonMap.runtimeType}');

  Person person = Person.fromJson(jsonMap);

  print(
      'person name is ${person.name}, age is ${person.age}, height is ${person.height}');

  return person;
}

JSON和Map互转

添加引用

import 'dart:convert';

JSON字符串转Map

Map<String, dynamic> user = JSON.decode(json);

print('Howdy, ${user['name']}!');
print('We sent the verification link to ${user['email']}.');

对象转JSON字符串

String json = JSON.encode(user);

JSON字符串转Model类

简单对象转换

json

{
    "name":  "jack",
    "age":  18,
    "height":  175.0
}

实体类

class Person {
  String name;
  int age;
  double height;

  Person({this.name, this.age, this.height});

  factory Person.fromJson(Map<String, dynamic> json) {
    return Person(name: json['name'], age: json['age'], height: json['height']);
  }
}

调用

final jsonMap = json.decode(personJson);
print('jsonMap runType is ${jsonMap.runtimeType}');
Person person = Person.fromJson(jsonMap);

输出如下

jsonMap runType is _InternalLinkedHashMap<String, dynamic>

可以看出 json.decode(personJson) 方法返回的类型为 _InternalLinkedHashMap ,意思就是这个 Map 的 key 为 String 类型，而 value 的类型为 dynamic 的，也就是动态的

数组的转换

[
  {
    "id": 1,
    "name": "Jack"
  },
  {
    "id": 2,
    "name": "Rose"
  }
]

实体类

class MemberList {  
  List<Member> memberList;  
  
  MemberList({this.memberList});  
  
  factory MemberList.fromJson(List<dynamic> listJson) {  
  
  List<Member> memberList =  
        listJson.map((value) => Member.fromJson(value)).toList();  
  
  return MemberList(memberList: memberList);  
  }  
}  
  
class Member {  
  int id;  
  String name;  
  
  Member({this.id, this.name});  
  
  factory Member.fromJson(Map<String, dynamic> json) {  
  return Member(id: json['id'], name: json['name']);  
  }  
}

调用

List<dynamic> list = json.decode(memberListJson);
MemberList memberList = MemberList.fromJson(list);
memberList.memberList
    .forEach((member) => print('member name is ${member.name}'));

带有数组的对象转换

{
    "name": "China",
    "cities": [
        "Beijing",
        "Shanghai"
    ]
}

实体类

class Country {  
  String name;  
  List<String> cities;  
  
  Country({this.name, this.cities});  
  
  factory Country.fromJson(Map<String, dynamic> json) {
    var originList = json['cities'];
    List<String> cityList = new List<String>.from(originList);
    return Country(name: json['name'], cities: cityList);
  } 
}

调用

Map<String, dynamic> jsonMap = json.decode(countryJson);
Country country = Country.fromJson(jsonMap);

复杂的对象数组嵌套

json

{
  "id": "0302",
  "class_name": "三年二班",
  "students": [
    {
      "name": "叶湘伦",
      "sex": "男"
    },
    {
      "name": "路小雨",
      "sex": "女"
    }
  ]
}

实体

class ClassInfo {
  String id;
  String name;
  List<Student> studentList;

  ClassInfo({this.id, this.name, this.studentList});

  factory ClassInfo.fromJson(Map<String, dynamic> json) {  
      final originList = json['students'] as List;  
      List<Student> studentList =  
          originList.map((value) => Student.fromJson(value)).toList();  
      return ClassInfo(id: json['id'], name: json['class_name'], studentList: studentList);  
  }
}

class Student {
  String name;
  String sex;

  Student({this.name, this.sex});

  factory Student.fromJson(Map<String, dynamic> json) {
    return Student(name: json['name'], sex: json['sex']);
  }
}

调用

Map<String, dynamic> jsonMap = json.decode(classInfoJson);

ClassInfo classInfo = ClassInfo.fromJson(jsonMap);
classInfo.studentList
    .forEach((student) => print('student name is ${student.name}'));

使用插件生成实体类

FlutterJsonBeanFactory插件

除了上面的方式外，我们还可以使用FlutterJsonBeanFactory插件来辅助生成Bean类。安装FlutterJsonBeanFactory插件很简单，

以Android Studio为例，

依次选择【Android Studio】->【Settings】->【Plugins】，然后搜索FlutterJsonBeanFactory插件安装即可

使用方式

在要生成文件的文件夹上右键New -> dart bean class File from JSON

该插件转换要求JSON的最外层为对象，不能为数组，为数组时无法转换。

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原始发表：2020-05-09，如有侵权请联系 cloudcommunity@tencent.com 删除

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