面试题：Flutter dio插件复杂网络请求的异常处理与重试机制

Question

在Flutter应用里，使用dio插件进行复杂网络请求时，可能会遇到网络波动、服务器响应超时等异常情况。请描述如何优雅地处理这些异常，并实现一个简单的重试机制，当请求失败时能自动重试一定次数，详细说明设计思路和实现代码。

Answer 1

设计思路

1. 异常捕获：使用try-catch块捕获Dio请求过程中可能抛出的异常，如网络波动导致的DioErrorType.connectionError、服务器响应超时导致的DioErrorType.connectTimeout和DioErrorType.receiveTimeout等。
2. 重试机制：设定最大重试次数，当捕获到异常时，判断是否达到最大重试次数，如果未达到则进行重试，达到则抛出最终异常。

实现代码

import 'package:dio/dio.dart';

class RetryDio {
  final Dio dio;
  final int maxRetries;

  RetryDio({required this.dio, required this.maxRetries});

  Future<Response> retryRequest(RequestOptions options) async {
    int retryCount = 0;
    while (retryCount < maxRetries) {
      try {
        return await dio.request(options.path,
            data: options.data,
            queryParameters: options.queryParameters,
            options: options);
      } on DioError catch (e) {
        if (e.type == DioErrorType.connectionError ||
            e.type == DioErrorType.connectTimeout ||
            e.type == DioErrorType.receiveTimeout) {
          retryCount++;
          if (retryCount >= maxRetries) {
            throw e;
          }
          print('Retry attempt $retryCount due to: ${e.message}');
        } else {
          throw e;
        }
      }
    }
    throw Exception('Max retry attempts reached');
  }
}

使用示例：

void main() async {
  Dio dio = Dio();
  RetryDio retryDio = RetryDio(dio: dio, maxRetries: 3);
  try {
    Response response = await retryDio.retryRequest(RequestOptions(path: 'your_api_url'));
    print(response.data);
  } catch (e) {
    print('Final error: $e');
  }
}