c# - DelegateHandler 的 DI 无法正常工作

Question

刚开始使用 HttpFactory，并且非常困惑它的 DI 是如何工作的，例如这一行工作

services.AddHttpClient<IMyClient, MyClient>()
   .AddHttpMessageHandler(s => new UserAgentDelegatingHandler());

这不是

services.AddHttpClient<IMyClient, MyClient>()
  .AddHttpMessageHandler<UserAgentDelegatingHandler>();

返回

"Message: System.InvalidOperationException : No service for type 'UserAgentDelegatingHandler' has been registered."

同样的情况，下面的代码工作正常

services.AddHttpContextAccessor();
services.AddHttpClient<IMyClient, MyClient>()
   .AddHttpMessageHandler(s => new CookieDelegateHandler(s.GetRequiredService<IHttpContextAccessor>()));

但这不是

services.AddHttpContextAccessor();
services.AddHttpClient<IMyClient, MyClient>()
   .AddHttpMessageHandler<CookieDelegateHandler>();

我阅读了很多 HttpClientFactory 用法示例，我的 DelegateHandlers 来自这些示例。

我做错了什么？

Answer 1

return "Message: System.InvalidOperationException : No service for type 'UserAgentDelegatingHandler' has been registered."

如该错误所示，您需要注册 UserAgentDelegatingHandler当你使用 .AddHttpMessageHandler<UserAgentDelegatingHandler>() .

检查 AddHttpMessageHandler ，你会发现

The type of the DelegatingHandler. The handler type must be registered as a transient service.

试着改变你的代码

services.AddTransient<UserAgentDelegatingHandler>();
services.AddHttpClient<IMyClient, MyClient>()
        .AddHttpMessageHandler<UserAgentDelegatingHandler>();