如标题所示。
假设我注册了一个强类型的客户端,例如
var services = new ServiceCollection();
//A named client is another option that could be tried since MSDN documentation shows that being used when IHttpClientFactory is injected.
//However, it appears it gives the same exception.
//services.AddHttpClient("test", httpClient =>
services.AddHttpClient<TestClient>(httpClient =>
{
httpClient.BaseAddress = new Uri("");
});
.AddHttpMessageHandler(_ => new TestMessageHandler());
//Registering IHttpClientFactory isn't needed, hence commented.
//services.AddSingleton(sp => sp.GetRequiredService<IHttpClientFactory>());
var servicesProvider = services.BuildServiceProvider(validateScopes: true);
public class TestClient
{
private IHttpClientFactory ClientFactory { get; }
public TestClient(IHttpClientFactory clientFactory)
{
ClientFactory = clientFactory;
}
public async Task<HttpResponseMessage> CallAsync(CancellationToken cancellation = default)
{
//using(var client = ClientFactory.CreateClient("test"))
using(var client = ClientFactory.CreateClient())
{
return await client.GetAsync("/", cancellation);
}
}
}
// This throws with "Message: System.InvalidOperationException : A suitable constructor
// for type 'Test.TestClient' could not be located. Ensure the type is concrete and services
// are registered for all parameters of a public constructor.
var client = servicesProvider.GetService<TestClient>();
但如评论中所述,将抛出异常。我是否遗漏了一些显而易见的事情,或者这种安排是不可能的?
client
时会抛出 NullReferenceException
。奇怪,奇怪。
<编辑 2:我正在考虑避免的场景也在 https://github.com/aspnet/Extensions/issues/924 中进行了描述和讨论。也许那里的书写方式是一种避免某些问题的方式,也许不太令人满意。
这发生在 XUnit 项目中,可能与问题无关,但谁知道呢。 :)
<编辑 3:显示问题的控制台程序。
using Microsoft.Extensions.DependencyInjection;
using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
namespace TypedClientTest
{
public class TestClient
{
private IHttpClientFactory ClientFactory { get; }
public TestClient(IHttpClientFactory clientFactory)
{
ClientFactory = clientFactory;
}
public async Task<HttpResponseMessage> TestAsync(CancellationToken cancellation = default)
{
using (var client = ClientFactory.CreateClient())
{
return await client.GetAsync("/", cancellation);
}
}
}
class Program
{
static void Main(string[] args)
{
var services = new ServiceCollection();
services
.AddHttpClient<TestClient>(httpClient => httpClient.BaseAddress = new Uri("https://www.github.com/"));
var servicesProvider = services.BuildServiceProvider(validateScopes: true);
//This throws that there is not a suitable constructor. Should it?
var client = servicesProvider.GetService<TestClient>();
}
}
}
使用 install-package Microsoft.Extensions.Http
和 install-package Microsoft.Extensions.DependencyInjection
。
同样在异常堆栈中读取
at System.Threading.LazyInitializer.EnsureInitializedCore[T](T& target, Boolean& initialized, Object& syncLock, Func
1 valueFactory) at Microsoft.Extensions.Http.DefaultTypedHttpClientFactory
1.Cache.get_Activator() at ** Microsoft.Extensions.Http.DefaultTypedHttpClientFactory1.CreateClient(HttpClient httpClient) ** at System.Threading.LazyInitializer.EnsureInitializedCore[T](T& target, Boolean& initialized, Object& syncLock, Func
1 valueFactory) at Microsoft.Extensions.Http.DefaultTypedHttpClientFactory1.Cache.get_Activator() at Microsoft.Extensions.Http.DefaultTypedHttpClientFactory
1.CreateClient(HttpClient httpClient) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitTransient(TransientCallSite transientCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider) at TypedClientTest.Program.Main(String[] args) in C:\projektit\testit\TypedClientTest\TypedClientTest\Program.cs:line 40
这当然指向问题所在。但可能需要进一步调试。
现在可能有一些方法可以解决这个问题。 :)
<编辑 5:
因此,它似乎为具有 IHttpClientFactory
的类型化客户端调用 .AddHttpClient
,最终出现在“奇怪的地方”。事实上,不可能使用 IHttpClientFactory
来创建自己类型的类型化客户端。
使用命名客户端实现这一点的一种方法可能是这样的
public static class CustomServicesCollectionExtensions
{
public static IHttpClientBuilder AddTypedHttpClient<TClient>(this IServiceCollection serviceCollection, Action<HttpClient> configureClient) where TClient: class
{
//return serviceCollection.Add(new ServiceDescriptor(typeof(TClient).Name, f => new ...,*/ ServiceLifetime.Singleton));
servicesCollection.AddTransient<TClient>();
return serviceCollection.AddHttpClient(typeof(TType).Name, configureClient);
}
}
public static class HttpClientFactoryExtensions
{
public static HttpClient CreateClient<TClient>(this IHttpClientFactory clientFactory)
{
return clientFactory.CreateClient(typeof(TClient).Name);
}
}
public class TestClient
{
private IHttpClientFactory ClientFactory { get; }
public TestClient(IHttpClientFactory clientFactory)
{
ClientFactory = clientFactory;
}
public async Task<HttpResponseMessage> Test(CancellationToken cancellation = default)
{
using(var client = ClientFactory.CreateClient<TestClient>())
{
return await client.GetAsync("/", cancellation);
}
}
}
模仿扩展方法已经做的事情。当然,现在也可以更好地公开生命周期服务。
最佳答案
请阅读 Typed clients :
A typed client accepts a HttpClient parameter in its constructor
代替 IHttpClientFactory
,您的类应该在其构造函数中接受 HttpClient
,它将由 DI 提供(通过 AddHttpClient
扩展启用) .
public class TestClient
{
private HttpClient Client { get; }
public TestClient(HttpClient client)
{
Client = client;
}
public Task<HttpResponseMessage> CallAsync(CancellationToken cancellation = default)
{
return client.GetAsync("/", cancellation);
}
}
编辑
(基于以上修改)
如果你想覆盖 AddHttpClient
扩展方法的默认行为,那么你应该直接注册你的实现:
var services = new ServiceCollection();
services.AddHttpClient("test", httpClient =>
{
httpClient.BaseAddress = new Uri("https://localhost");
});
services.AddScoped<TestClient>();
var servicesProvider = services.BuildServiceProvider(validateScopes: true);
using (var scope = servicesProvider.CreateScope())
{
var client = scope.ServiceProvider.GetRequiredService<TestClient>();
}
public class TestClient
{
private IHttpClientFactory ClientFactory { get; }
public TestClient(IHttpClientFactory clientFactory)
{
ClientFactory = clientFactory;
}
public Task<HttpResponseMessage> CallAsync(CancellationToken cancellation = default)
{
using (var client = ClientFactory.CreateClient("test"))
{
return client.GetAsync("/", cancellation);
}
}
}
关于c# - 是否可以将 IHttpClientFactory 注入(inject)强类型客户端?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/56739903/