c# - 是否可以将IHttpClientFactory注入(inject)强类型的客户端？

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>();

但是，正如评论中指出的那样，将引发异常。我会错过令人生厌的东西吗？或者这种安排不可能吗？

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

https://github.com/aspnet/Extensions/issues/924中也进行了描述和讨论，也许编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>();
    }
}
}

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

同样在异常堆栈中读取



哪个当然指向问题。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https://github.com/aspnet/Extensions/blob/11cf90103841c35cbefe9afb8e5bf9fee696dd17/src/HttpClientFactory/Http/src/DependencyInjection/HttpClientFactoryServiceCollectionExtensions.cs中通常可见。

现在可能有一些方法可以解决此问题。 :)


因此，似乎为一个类型为.AddHttpClient的客户端终止于“奇怪的地方”而调用IHttpClientFactory。实际上，不可能使用IHttpClientFactory创建自己类型的类型化客户端。

与命名客户端实现此目的的一种方法可能是:

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);
        }
    }
}

哪个模仿了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。

最佳答案

请阅读有关Typed clients的信息:



您的类应该在其构造函数中接受IHttpClientFactory而不是HttpClient，这将由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)

如果要覆盖AddHttpClient扩展方法的默认行为，则应直接注册您的实现:

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)强类型的客户端？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/56739903/