Swift 联合处理 HTTP 状态码错误

Question

我正在阅读这篇文章:https://www.raywenderlich.com/4161005-mvvm-with-combine-tutorial-for-ios关于如何使用 combine 的 Ray Wenderlich。他们有一个示例，它从 API 获取数据但不处理 HTTP 状态代码。我想添加它，但到目前为止我还做不到。

根据这个答案，您可以添加一个 tryMap，但随后 XCode 开始显示如下错误:无法推断通用参数“T”。

代码下方:

extension WeatherFetcher: WeatherFetchable {
  func weeklyWeatherForecast(
    forCity city: String
  ) -> AnyPublisher<WeeklyForecastResponse, WeatherError> {
    return forecast(with: makeWeeklyForecastComponents(withCity: city))
  }

  private func forecast<T>(
    with components: URLComponents
  ) -> AnyPublisher<T, WeatherError> where T: Decodable {
    guard let url = components.url else {
      let error = WeatherError.network(description: "Couldn't create URL")
      return Fail(error: error).eraseToAnyPublisher()
    }
    return session.dataTaskPublisher(for: URLRequest(url: url))
      .mapError { error in
        .network(description: error.localizedDescription)
    }
    .flatMap(maxPublishers: .max(1)) { pair in
      decode(pair.data)
    }
    .eraseToAnyPublisher()
  }
}

我想添加

.tryMap { data, response in
    guard let httpResponse = response as? HTTPURLResponse,
        200..<300 ~= httpResponse.statusCode else {
            switch (response as! HTTPURLResponse).statusCode {
            case (400...499):
                throw ServiceErrors.internalError((response as! HTTPURLResponse).statusCode)
            default:
                throw ServiceErrors.serverError((response as! HTTPURLResponse).statusCode)
            }
    }
    return data
}

Answer 1

我认为您可以简单地将 flatMap block 替换为 tryMap。而不是从 tryMap 返回数据，它应该解码为 T。所以 return data 行应该是 return try JSONDecoder().decode(T.self, from : 数据)

private func forecast<T>(with components: URLComponents) -> AnyPublisher<T, WeatherError> where T: Decodable {
guard let url = components.url else {
    let error = WeatherError.network(description: "Couldn't create URL")
    return Fail(error: error).eraseToAnyPublisher()
}
return session.dataTaskPublisher(for: URLRequest(url: url))
    .tryMap { data, response in
        guard let httpResponse = response as? HTTPURLResponse,
            200..<300 ~= httpResponse.statusCode else {
                switch (response as! HTTPURLResponse).statusCode {
                case (400...499):
            throw ServiceErrors.internalError((response as! HTTPURLResponse).statusCode)
                default:
                    throw ServiceErrors.serverError((response as! HTTPURLResponse).statusCode)
                }
        }
        return try JSONDecoder().decode(T.self, from: data)
}
.mapError { error in
    WeatherError() // some kind of error
}
.eraseToAnyPublisher()