Question

如标题所示。

假设我注册了一个像这样的强类型客户端

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>();

但是，如注释中所述，将引发异常。我会错过令人讨厌的东西吗？还是这种安排是不可能的？

IHttpClientFactory，则在尝试解析NullReferenceException时会抛出client。奇怪，奇怪。

https://github.com/aspnet/Extensions/issues/924上也描述并讨论了我想避免的情况，也许那里写的方式是一种避免某些问题的方式，但可能不令人满意。

这发生在XUnit项目中，可能与问题无关，但谁知道。：）

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>();
    }
}
}

带有install-package Microsoft.Extensions.Http和install-package Microsoft.Extensions.DependencyInjection。

也在异常堆栈中读取

at System.Threading.LazyInitializer.EnsureInitializedCore [T]（T＆目标，布尔值和初始化，对象和同步锁，功能1 valueFactory) at Microsoft.Extensions.Http.DefaultTypedHttpClientFactory 1.Cache.get_Activator（）在** Microsoft.Extensions.Http.DefaultTypedHttpClientFactory 1.CreateClient(HttpClient httpClient) ** at System.Threading.LazyInitializer.EnsureInitializedCore[T](T& target, Boolean& initialized, Object& syncLock, Func 1 valueFactory）在Microsoft.Extensions.Http.DefaultTypedHttpClientFactory 1.Cache.get_Activator() at Microsoft.Extensions.Http.DefaultTypedHttpClientFactory 1.CreateClient（HttpClient httpClient）在Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitTransient（TransientCallSite transitionCallSite，ServiceProviderEngineScope范围）在Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService [T]（IServiceProvider提供程序）在C：\ projektit \ testit \ TypedClientTest \ TypedClientTest \ Program.cs：line 40中的TypedClientTest.Program.Main（String [] args）处

当然可以指出问题所在。但是可能需要进一步调试。

https://github.com/aspnet/Extensions/blob/557995ec322f1175d6d8a72a41713eec2d194871/src/HttpClientFactory/Http/src/DefaultTypedHttpClientFactory.cs#L47和总体上在https://github.com/aspnet/Extensions/blob/11cf90103841c35cbefe9afb8e5bf9fee696dd17/src/HttpClientFactory/Http/src/DependencyInjection/HttpClientFactoryServiceCollectionExtensions.cs上可见。

现在可能有一些方法可以解决此问题。：）

<编辑5：

因此，似乎呼叫.AddHttpClient的类型为IHttpClientFactory的客户端最终出现在“奇怪的地方”。实际上，不可能使用IHttpClientFactory创建自己类型的类型化客户端。

使用命名客户端进行此操作的一种方法可能是

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);
        }
    }
}

模仿扩展方法已经完成的工作。当然，现在也可以更好地公开终生服务。

Answer 1

请阅读有关Typed clients的信息：

类型化的客户端在其构造函数中接受HttpClient参数

您的类应该在其构造函数中接受IHttpClientFactory而不是HttpClient，该构造函数将由DI提供（使用AddHttpClient扩展名启用）。

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）

如果您想覆盖AddHttpClient扩展方法的默认行为，则应直接注册实现：

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);
        }
    }
}

是否可以将IHttpClientFactory注入强类型的客户端？

1 个答案:

编辑