ASP.NET 核心类型客户端中的 IHttpClientFactory

Question

当我尝试使用 HttpClient 的类型化客户端时收到错误消息，如下所述： https://docs.microsoft.com/en-us/aspnet/core/fundamentals/http-requests?view=aspnetcore-2.2

这是我的设置：

Startup.cs:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

    services.AddDefaultAWSOptions(Configuration.GetAWSOptions());

    services.AddHttpClient<IPStackService>(c =>
    {
        c.BaseAddress = new Uri(Configuration["IPStackURL"]);
    });

    services.AddHttpContextAccessor();

    services.AddTransient<IIPStackService, IPStackService>();
}

控制器：

[Route("api/[controller]")]
    [ApiController]
    public class RenderController : ControllerBase
    {
        private IConfiguration _configuration;
        private readonly ILogger _logger;
        private IIPStackService _ipMetaDataService;

        public RenderController(IConfiguration configuration,
                                ILogger<RenderController> logger,
                                IIPStackService ipStackService)
        {
            _configuration = configuration;
            _ipStackService = ipStackService;
            _logger = logger;
        }

        [HttpGet]
        [ProducesResponseType(StatusCodes.Status200OK)]
        [Produces("text/plain")]
        public async Task<ActionResult> GetAsync(string hostId, string clientUtc)
        {
            var ip = Common.ResolveIPAddress(HttpContext);

            var ipMetaData = await _ipStackService.GetByIPAsync(ip, _configuration["AccessKey"]);

            // removed for clarity

            return allowed ? Ok(true) : Ok(null);
        }
    }

服务：

public class IPStackService : IIPStackService
{
    private readonly ILogger _logger;
    private readonly HttpClient _httpClient;

    public IPStackService(ILogger<IPStackService> logger, HttpClient client)
    {
        _logger = logger;
        _httpClient = client;
    }

    public async Task<IPMetaDataModel> GetByIPAsync(string ip, string accessKey)
    {
        var ipMetaData = new IPMetaDataModel();

        var response = await _httpClient.GetAsync($"/{ip}?access_key={accessKey}");
        response.EnsureSuccessStatusCode();

        // removed for clarity

        return ipMetaData;
    }
}

收到错误：

An unhandled exception occurred while processing the request. InvalidOperationException: Unable to resolve service for type 'System.Net.Http.HttpClient' while attempting to activate 'WebScreen.Gate.Services.IPStackService'. Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateArgumentCallSites(Type serviceType, Type implementationType, CallSiteChain callSiteChain, ParameterInfo[] parameters, bool throwIfCallSiteNotFound)

如何为 HttpClient 正确设置类型化客户端？

Answer 1

IPStackService 的 Activator（代码反射）无法在 DI 集合中找到 HttpClient，这就是您遇到异常的原因（特别针对 services.AddTransient<IIPStackService, IPStackService>()）。

顺便说一句，您在 DI 集合中添加了两次服务 IPStackService：

services.AddHttpClient<IPStackService>(...);.
services.AddTransient<IIPStackService, IPStackService>();

你只需要一个，因为你使用的是类型化客户端，你可以通过删除第二个并保留第一个来解决你的问题，并通过将合同添加到实现中来稍微改变第一个，如下所示:

services.AddHttpClient<IIPStackService, IPStackService>(c =>
{
     c.BaseAddress = new Uri(Configuration["IPStackURL"]);
});

AddHttpClient 将负责将 HttpClient 绑定到您的服务。

如果您想使用 services.AddTransient<IIPStackService, IPStackService>(); 而不是 services.AddHttpClient，那么您需要将 HttpClient 添加到您的 DI 集合中：

services.AddTransient<HttpClient>();

ASP.NET 核心类型客户端中的 IHttpClientFactory

IHttpClientFactory in ASP.NET Core Typed Clients

c#

dependency-injection

dotnet-httpclient

asp.net-core

asp.net-core-2.1