Flutter完整的Dio网络框架null空安全二次封装。

所需依赖添加在项目中的pubspec.yaml中：

dio: ^4.0.6                                       #网络请求
connectivity_plus: ^2.3.6                         #网络监测
pretty_dio_logger: ^1.1.1                         #日志打印

class HttpRequest {
  // 单例模式使用Http类，
  static final HttpRequest _instance = HttpRequest._internal();

  factory HttpRequest() => _instance;

  static late final Dio dio;

  /// 内部构造方法
  HttpRequest._internal() {
    /// 初始化dio
    BaseOptions options = BaseOptions(
        connectTimeout: HttpOptions.connectTimeout,
        receiveTimeout: HttpOptions.receiveTimeout,
        sendTimeout: HttpOptions.sendTimeout,
        baseUrl: HttpOptions.baseUrl);
    dio = Dio(options);

    /// 添加各种拦截器
    dio.interceptors.add(ErrorInterceptor());
    dio.interceptors.add(PrettyDioLogger(
        requestHeader: true,
        requestBody: true,
        responseHeader: true,
        responseBody: true));
  }

  /// 封装request方法
  Future request({
    required String path,
    required HttpMethod method,
    dynamic data,
    Map? queryParameters,
    bool showLoading = true,
    bool showErrorMessage = true,
  }) async {
    const Map methodValues = {
      HttpMethod.get: 'get',
      HttpMethod.post: 'post',
      HttpMethod.put: 'put',
      HttpMethod.delete: 'delete',
      HttpMethod.patch: 'patch',
      HttpMethod.head: 'head'
    };

    //动态添加header头
    Map headers = Map();
    headers["version"] = "1.0.0";
 

    Options options = Options(
      method: methodValues[method],
      headers: headers,
    );

    try {
      if (showLoading) {
        EasyLoading.show(status: 'loading...');
      }
      Response response = await HttpRequest.dio.request(
        path,
        data: data,
        queryParameters: queryParameters,
        options: options,
      );
      return response.data;
    } on DioError catch (error) {
      HttpException httpException = error.error;
      if (showErrorMessage) {
        EasyLoading.showToast(httpException.msg);
      }
    } finally {
      if (showLoading) {
        EasyLoading.dismiss();
      }
    }
  }
}

enum HttpMethod {
  get,
  post,
  delete,
  put,
  patch,
  head,
}

class ErrorInterceptor extends Interceptor {
  @override
  void onError(DioError err, ErrorInterceptorHandler handler) async {
    /// 根据DioError创建HttpException
    HttpException httpException = HttpException.create(err);

    /// dio默认的错误实例，如果是没有网络，只能得到一个未知错误，无法精准的得知是否是无网络的情况
    /// 这里对于断网的情况，给一个特殊的code和msg
    if (err.type == DioErrorType.other) {
      var connectivityResult = await (Connectivity().checkConnectivity());
      if (connectivityResult == ConnectivityResult.none) {
        httpException = HttpException(code: -100, msg: 'None Network.');
      }
    }

    /// 将自定义的HttpException
    err.error = httpException;

    /// 调用父类，回到dio框架
    super.onError(err, handler);
  }
}

class HttpException implements Exception {
  final int code;
  final String msg;

  HttpException({
    this.code = -1,
    this.msg = 'unknow error',
  });

  @override
  String toString() {
    return 'Http Error [$code]: $msg';
  }

  factory HttpException.create(DioError error) {
    /// dio异常
    switch (error.type) {
      case DioErrorType.cancel:
        {
          return HttpException(code: -1, msg: 'request cancel');
        }
      case DioErrorType.connectTimeout:
        {
          return HttpException(code: -1, msg: 'connect timeout');
        }
      case DioErrorType.sendTimeout:
        {
          return HttpException(code: -1, msg: 'send timeout');
        }
      case DioErrorType.receiveTimeout:
        {
          return HttpException(code: -1, msg: 'receive timeout');
        }
      case DioErrorType.response:
        {
          try {
            int statusCode = error.response?.statusCode ?? 0;
            // String errMsg = error.response.statusMessage;
            // return ErrorEntity(code: errCode, message: errMsg);
            switch (statusCode) {
              case 400:
                {
                  return HttpException(code: statusCode, msg: 'Request syntax error');
                }
              case 401:
                {
                  return HttpException(code: statusCode, msg: 'Without permission');
                }
              case 403:
                {
                  return HttpException(code: statusCode, msg: 'Server rejects execution');
                }
              case 404:
                {
                  return HttpException(code: statusCode, msg: 'Unable to connect to server');
                }
              case 405:
                {
                  return HttpException(code: statusCode, msg: 'The request method is disabled');
                }
              case 500:
                {
                  return HttpException(code: statusCode, msg: 'Server internal error');
                }
              case 502:
                {
                  return HttpException(code: statusCode, msg: 'Invalid request');
                }
              case 503:
                {
                  return HttpException(code: statusCode, msg: 'The server is down.');
                }
              case 505:
                {
                  return HttpException(code: statusCode, msg: 'HTTP requests are not supported');
                }
              default:
                {
                  return HttpException(
                      code: statusCode, msg: error.response?.statusMessage ?? 'unknow error');
                }
            }
          } on Exception catch (_) {
            return HttpException(code: -1, msg: 'unknow error');
          }
        }
      default:
        {
          return HttpException(code: -1, msg: error.message);
        }
    }
  }
}

class HttpOptions {
  /// 超时时间；单位是ms
  static const int connectTimeout = 15000;
  static const int receiveTimeout = 15000;
  static const int sendTimeout = 15000;

  /// 地址域名前缀
  static const String baseUrl = '************';

}

/// 调用底层的request，重新提供get，post等方便方法
class HttpUtils {
  static HttpRequest httpRequest = HttpRequest();

  /// get
  static Future get({
    required String path,
    Map? queryParameters,
    bool showLoading = true,
    bool showErrorMessage = true,
  }) {
    return httpRequest.request(
      path: path,
      method: HttpMethod.get,
      queryParameters: queryParameters,
      showLoading: showLoading,
      showErrorMessage: showErrorMessage,
    );
  }

  /// post
  static Future post({
    required String path,
    required HttpMethod method,
    dynamic data,
    bool showLoading = true,
    bool showErrorMessage = true,
  }) {
    return httpRequest.request(
      path: path,
      method: HttpMethod.post,
      data: data,
      showLoading: showLoading,
      showErrorMessage: showErrorMessage,
    );
  }

}