如何正确使用ICachedServiceProvider注入Typed HttpClient？

使用Typed HttpClient时，尝试通过ICachedServiceProvider直接获取HttpClient实例：

var httpClient = _cachedServiceProvider.GetRequiredService<HttpClient>();

执行时抛出以下异常：

System.InvalidOperationException
An invalid request URI was provided. Either the request URI must be an absolute URI or BaseAddress must be set.
at System.Net.Http.HttpClient.PrepareRequestMessage(HttpRequestMessage request)

但通过构造函数注入Typed HttpClient却能正常运行：

private readonly HttpClient _httpClient;

public TestService(HttpClient httpClient)
{
    _httpClient = httpClient;
}

ConfigureServices中的配置如下：

private void ConfigureHttpClient(ServiceConfigurationContext context)
{
    var options = context.Services.ExecutePreConfiguredActions<TestOptions>();
    context.Services.AddHttpClient<ITestService, TestService>(httpClient =>
    {
        httpClient.BaseAddress = options.BaseAddress;
    });
}

请问如何正确通过ICachedServiceProvider获取配置好的Typed HttpClient？

你已经找到的通过IHttpClientFactory获取命名HttpClient的方案是正确的，代码如下：

var httpClientFactory = _cachedServiceProvider.GetRequiredService<IHttpClientFactory>();
var httpClient = httpClientFactory.CreateClient(nameof(ITestService));
// ...
var response = await httpClient.PostAsJsonAsync("oauth/token", testRequest);

原因说明 #

直接调用GetRequiredService<HttpClient>()获取到的是默认的无配置HttpClient实例，并没有绑定你通过AddHttpClient<ITestService, TestService>配置的BaseAddress等参数。

当你使用AddHttpClient<TInterface, TImplementation>注册Typed Client时，ASP.NET Core会做两件事：

1. 为TImplementation类型注入一个已配置好的HttpClient实例
2. 同时以TInterface的类型名称（即nameof(ITestService)）作为客户端名称，将配置好的HttpClient注册到IHttpClientFactory中

因此通过IHttpClientFactory.CreateClient(nameof(ITestService))，就能拿到和构造函数注入时完全一致的、已配置BaseAddress的HttpClient实例。

内容的提问来源于stack exchange，提问作者Jakeuj