transformer.dart

import 'dart:async';

import 'package:diox/diox.dart';

/// If the request data is a `List` type, the [DefaultTransformer] will send data
/// by calling its `toString()` method. However, normally the List object is
/// not expected for request data( mostly need Map ). So we provide a custom
/// [Transformer] that will throw error when request data is a `List` type.

class MyTransformer extends DefaultTransformer {
  @override
  Future<String> transformRequest(RequestOptions options) async {
    if (options.data is List<String>) {
      throw DioError(
        error: "Can't send List to sever directly",
        requestOptions: options,
      );
    } else {
      return super.transformRequest(options);
    }
  }

  /// The [Options] doesn't contain the cookie info. we add the cookie
  /// info to [Options.extra], and you can retrieve it in [ResponseInterceptor]
  /// and [Response] with `response.request.extra["cookies"]`.
  @override
  Future transformResponse(
    RequestOptions options,
    ResponseBody response,
  ) async {
    options.extra['self'] = 'XX';
    return super.transformResponse(options, response);
  }
}

void main() async {
  final dio = Dio();
  // Use custom Transformer
  dio.transformer = MyTransformer();

  final response = await dio.get('https://www.baidu.com');
  print(response.requestOptions.extra['self']);

  try {
    await dio.post('https://www.baidu.com', data: ['1', '2']);
  } catch (e) {
    print(e);
  }
}