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Flutter网络请求：Retrofit使用指南

Retrofit是Android平台上广受欢迎的HTTP客户端库，在Flutter中可以通过retrofit包实现类似的网络请求功能。下面是完整的使用指南：

1. 添加依赖

首先在pubspec.yaml中添加所需依赖：

dependencies:retrofit: ^4.0.1dio: ^5.3.2json_annotation: ^4.8.1dev_dependencies:retrofit_generator: ^4.0.1build_runner: ^2.4.4

2. 创建API接口

定义一个抽象类来描述你的API接口：

import 'package:retrofit/retrofit.dart';
import 'package:dio/dio.dart';
import 'package:json_annotation/json_annotation.dart';part 'api_service.g.dart';@RestApi(baseUrl: "https://jsonplaceholder.typicode.com/")
abstract class ApiService {factory ApiService(Dio dio, {String baseUrl}) = _ApiService;@GET("/posts")Future<List<Post>> getPosts();@GET("/posts/{id}")Future<Post> getPost(@Path("id") int id);@POST("/posts")Future<Post> createPost(@Body() Post post);
}@JsonSerializable()
class Post {final int id;final String title;final String body;final int userId;Post({required this.id,required this.title,required this.body,required this.userId,});factory Post.fromJson(Map<String, dynamic> json) => _$PostFromJson(json);Map<String, dynamic> toJson() => _$PostToJson(this);
}

3. 生成代码

运行以下命令生成实现代码：

flutter pub run build_runner build

这会生成api_service.g.dart文件。

4. 使用API服务

void main() async {final dio = Dio();final apiService = ApiService(dio);try {// 获取所有帖子final posts = await apiService.getPosts();print(posts);// 获取单个帖子final post = await apiService.getPost(1);print(post);// 创建新帖子final newPost = await apiService.createPost(Post(id: 101, title: 'New Post', body: 'Content', userId: 1),);print(newPost);} catch (e) {print(e);}
}

5. 高级功能

添加请求头

@GET("/posts")
@Headers({'Content-Type': 'application/json'})
Future<List<Post>> getPosts();

查询参数

@GET("/posts")
Future<List<Post>> getPostsByUser(@Query("userId") int userId);

表单数据

@POST("/login")
@FormUrlEncoded()
Future<User> login(@Field("username") String username,@Field("password") String password,
);

拦截器

final dio = Dio()..interceptors.add(InterceptorsWrapper(onRequest: (options, handler) {// 添加认证tokenoptions.headers['Authorization'] = 'Bearer token';return handler.next(options);},onError: (DioError e, handler) {// 错误处理return handler.next(e);},),);

6. 完整配置示例

import 'package:dio/dio.dart';
import 'package:retrofit/retrofit.dart';part 'api_service.g.dart';@RestApi(baseUrl: "https://api.example.com/v1/")
abstract class ApiService {factory ApiService(Dio dio, {String baseUrl}) {dio.options = BaseOptions(receiveTimeout: const Duration(seconds: 30),connectTimeout: const Duration(seconds: 30),);return _ApiService(dio, baseUrl: baseUrl);}@GET("users")Future<List<User>> getUsers();@GET("users/{id}")Future<User> getUser(@Path("id") String id);@POST("users")Future<User> createUser(@Body() User user);@PUT("users/{id}")Future<User> updateUser(@Path("id") String id, @Body() User user);@DELETE("users/{id}")Future<void> deleteUser(@Path("id") String id);
}

7. 错误处理

try {final response = await apiService.getUser('123');
} on DioError catch (e) {if (e.response != null) {print(e.response?.statusCode);print(e.response?.data);} else {print(e.message);}
}

8. 测试API服务

test('getPosts returns List<Post>', () async {final dio = DioAdapterMock();final apiService = ApiService(dio);when(dio.get('/posts')).thenAnswer((_) async => Response(data: [{'id': 1, 'title': 'Test', 'body': 'Content', 'userId': 1}],statusCode: 200,requestOptions: RequestOptions(path: '/posts'),));final posts = await apiService.getPosts();expect(posts, isA<List<Post>>());expect(posts.first.title, 'Test');
});

Retrofit为Flutter提供了类型安全的HTTP客户端实现，通过代码生成简化了网络请求的编写，同时保持了Dio的强大功能。