如何在 C 语言中使用 HttpClientFactory 解决构造函数的

System.InvalidOperationException：找不到类型“X”的合适构造函数。确保类型是具体的，并且公共构造函数的所有参数都注册为服务或作为参数传递。还要确保没有提供无关的参数。

如何解决？这很容易。但首先，让我向您展示我在错误版本中做了什么。

设置错误的示例

对于此示例，我创建了一个基本项目。
这是一个 .NET 7 API 项目，只有一个控制器，它调用接口中定义的另一个服务。GenderControllerIGenderizeService

public interface IGenderizeService
{
    Task<GenderProbability> GetGenderProbabiliy(string name);
}

IGenderizeService由一个类实现，该类是加载失败的类，因此会导致引发异常。该类调用外部终结点，分析结果，然后将其返回给调用方：GenderizeService

public class GenderizeService : IGenderizeService
{
    private readonly IHttpClientFactory _httpClientFactory;

    public GenderizeService(IHttpClientFactory httpClientFactory)
    {
        _httpClientFactory = httpClientFactory;
    }

    public async Task<GenderProbability> GetGenderProbabiliy(string name)
    {
        var httpClient = _httpClientFactory.CreateClient();

        var response = await httpClient.GetAsync($"?name={name}");

        var result = await response.Content.ReadFromJsonAsync<GenderProbability>();

        return result;
    }
}

最后，我在 Program 类中定义了服务，然后指定了哪个是在类中生成的 HttpClient 实例的基本 URL：GenderizeService

// some code

builder.Services.AddScoped<IGenderizeService, GenderizeService>();

builder.Services.AddHttpClient<IGenderizeService, GenderizeService>(
    client => client.BaseAddress = new Uri("https://api.genderize.io/")
    );

var app = builder.Build();

// some more code

That's it! Can you spot the error?

2 ways to solve the error

The error was quite simple, but it took me a while to spot:

In the constructor I was injecting an :IHttpClientFactory

public GenderizeService(IHttpClientFactory httpClientFactory)

while in the host definition I was declaring an for a specific class:HttpClient

builder.Services.AddHttpClient<IGenderizeService, GenderizeService>

Apparently, even if we've specified how to create an instance for a specific class, we could not build it using an IHttpClientFactory.

So, here are 2 ways to solve it.

Use named HttpClient in HttpClientFactory

Named HttpClients are a helpful way to define a specific HttpClient and use it across different services.

It's as simple as assigning a name to an HttpClient instance and then using the same name when you need that specific client.

So, define it in the Startup method:

builder.Services.AddHttpClient("genderize",
            client => client.BaseAddress = new Uri("https://api.genderize.io/")
        );

and retrieve it using :CreateClient

public GenderizeService(IHttpClientFactory httpClientFactory)
{
    _httpClientFactory = httpClientFactory;
}

public async Task<GenderProbability> GetGenderProbabiliy(string name)
{
    var httpClient = _httpClientFactory.CreateClient("genderize");

    var response = await httpClient.GetAsync($"?name={name}");

    var result = await response.Content.ReadFromJsonAsync<GenderProbability>();

    return result;
}