UWP中DI结合Refit与Polly处理ApiException编译报错求助

我在UWP应用中通过依赖注入配置了Refit客户端与Polly策略，初始代码如下：

var serviceCollection = new ServiceCollection();

serviceCollection
    .AddRefitClient(typeof(IClassevivaAPI))
    .ConfigureHttpClient(
        (sp, client) =>
        {
            client.BaseAddress = new Uri(Endpoint.CurrentEndpoint);
        }
    )
    .AddPolicyHandler(
        Policy<HttpResponseMessage>
            .HandleResult(r => r.StatusCode == System.Net.HttpStatusCode.Unauthorized)
            .RetryAsync(1)
    );

发现当HTTP响应状态非OK时Refit会抛出ApiException，于是添加了如下Polly策略：

.AddPolicyHandler(Policy<IApiResponse>
.Handle<ApiException>()
.RetryAsync(2)

编译时出现错误：

error CS1503: Argument 2: cannot convert from 'Polly.Retry.AsyncRetryPolicy<Refit.IApiResponse>' to 'Polly.IAsyncPolicy<System.Net.Http.HttpResponseMessage>'

错误原因 #

你添加的第二个策略是针对IApiResponse类型的，但当前AddPolicyHandler在HttpClientBuilder链式调用中，要求传入的是处理HttpResponseMessage的策略。因为AddRefitClient之后的HttpClient管道默认基于HttpResponseMessage，而Refit的IApiResponse级别策略需要用特定方式注册，两者类型不匹配导致编译失败。

解决方案 #

针对这个问题，有两种可行的解决思路：

方案一：注册针对HttpRequestMessage的异常处理策略 #

要处理Refit抛出的ApiException，需要将策略改为针对HttpRequestMessage类型，适配HttpClientBuilder的要求：

var serviceCollection = new ServiceCollection();

serviceCollection
    .AddRefitClient<IClassevivaAPI>()
    .ConfigureHttpClient((sp, client) =>
    {
        client.BaseAddress = new Uri(Endpoint.CurrentEndpoint);
    })
    // 保留原有针对Unauthorized状态的HttpResponseMessage策略
    .AddPolicyHandler(Policy<HttpResponseMessage>
        .HandleResult(r => r.StatusCode == System.Net.HttpStatusCode.Unauthorized)
        .RetryAsync(1))
    // 添加针对ApiException的策略，改为处理HttpRequestMessage
    .AddPolicyHandler(Policy<HttpRequestMessage>
        .Handle<ApiException>()
        .RetryAsync(2));

方案二：禁用Refit自动抛异常，统一在HttpClient级别处理响应 #

配置Refit不自动抛出非OK状态的ApiException，这样所有响应状态都可以在HttpClient层面用Polly处理：

var serviceCollection = new ServiceCollection();

serviceCollection
    .AddRefitClient<IClassevivaAPI>(sp => new RefitSettings
    {
        // 关闭Refit自动抛异常，让响应直接进入Polly处理流程
        ThrowOnAnyError = false
    })
    .ConfigureHttpClient((sp, client) =>
    {
        client.BaseAddress = new Uri(Endpoint.CurrentEndpoint);
    })
    // 统一处理所有非成功响应
    .AddPolicyHandler(Policy<HttpResponseMessage>
        .HandleResult(r => !r.IsSuccessStatusCode)
        .RetryAsync(2))
    // 保留原有针对Unauthorized的重试策略
    .AddPolicyHandler(Policy<HttpResponseMessage>
        .HandleResult(r => r.StatusCode == System.Net.HttpStatusCode.Unauthorized)
        .RetryAsync(1));

内容的提问来源于stack exchange，提问作者Gabboxl