farmer_client/lib/utils/Request.dart

import 'dart:convert';

import 'package:dio/dio.dart';

class Response {
  late int code;
  String? message;
  dynamic data;

  Response({
    required this.code,
    this.message,
    this.data,
  });

  factory Response.fromJson(dynamic str) => Response.fromMap(jsonDecode(str) as Map<String, dynamic>);

  factory Response.fromMap(Map<String, dynamic> resp) => Response(
    code: resp['code'],
    message: resp['message'],
    data: resp['data'],
  );
}

Dio createRequest() {
  var options = BaseOptions(
    baseUrl: 'https://www.xx.com/api',
    connectTimeout: 5000,
    receiveTimeout: 3000,
  );

  var dio = Dio(options);
  dio.interceptors.add(InterceptorsWrapper(
      onRequest:(options, handler){
        // Do something before request is sent
        return handler.next(options); //continue
        // If you want to resolve the request with some custom data，
        // you can resolve a `Response` object eg: `handler.resolve(response)`.
        // If you want to reject the request with a error message,
        // you can reject a `DioError` object eg: `handler.reject(dioError)`
      },
      onResponse:(response,handler) {
        Response resp = Response.fromJson(response.data['data']);
        if (resp.code == 1000) {
          response.data = resp.data;
          return handler.next(response);
        } else {
          return handler.reject(response.data);
        }
      },
      onError: (DioError e, handler) {
        // Do something with response error
        return  handler.next(e);//continue
        // If you want to resolve the request with some custom data，
        // you can resolve a `Response` object eg: `handler.resolve(response)`.
      }
  ));

  return dio;
}

var instance = createRequest();

Future request (RequestOptions options) async {
  var resp = await instance.fetch(options);

  if (resp.data.runtimeType == String) {
    String dt = resp.data as String;
    dt.trim();
    if (dt.startsWith('{') && dt.endsWith('}')) {
      return jsonDecode(dt);
    }
    return dt;
  }

  return resp.data;
}