HttpClientFactory：带有附加构造函数参数的类型化 HttpClient

Question

使用HttpClientFactory，我们可以配置依赖注入来创建和管理HttpClients的生命周期：

public class GitHubService : IGitHubService
{
    public HttpClient Client { get; }

    public GitHubService(HttpClient client)
    {
        client.BaseAddress = new Uri("https://api.github.com/");
        // GitHub API versioning
        client.DefaultRequestHeaders.Add("Accept",
            "application/vnd.github.v3+json");
        // GitHub requires a user-agent
        client.DefaultRequestHeaders.Add("User-Agent",
            "HttpClientFactory-Sample");

        Client = client;
    }

    public async Task<IEnumerable<GitHubIssue>> GetAspNetDocsIssues()
    {
        var response = await Client.GetAsync(
            "/repos/aspnet/AspNetCore.Docs/issues?state=open&sort=created&direction=desc");

        response.EnsureSuccessStatusCode();

        using var responseStream = await response.Content.ReadAsStreamAsync();
        return await JsonSerializer.DeserializeAsync
            <IEnumerable<GitHubIssue>>(responseStream);
    }
}

然后我们在 Startup.cs 中配置 DI：

services.AddHttpClient<GitHubService>();

但是，如果类型化客户端有额外的构造函数参数，应该如何提供这些？ 例如，如果要传入存储库名称：

public class GitHubService : IGitHubService
{
    public HttpClient Client { get; }
    private readonly string _repositoryName;

    public GitHubService(HttpClient client, string repositoryName)
    {
        _repositoryName = repositoryName;

        client.BaseAddress = new Uri("https://api.github.com/");
        // GitHub API versioning
        client.DefaultRequestHeaders.Add("Accept",
            "application/vnd.github.v3+json");
        // GitHub requires a user-agent
        client.DefaultRequestHeaders.Add("User-Agent",
            "HttpClientFactory-Sample");

        Client = client;
    }

    public async Task<IEnumerable<GitHubIssue>> GetAspNetDocsIssues()
    {
        var response = await Client.GetAsync(
            $"/repos/aspnet/{_repositoryName}/issues?state=open&sort=created&direction=desc");

        response.EnsureSuccessStatusCode();

        using var responseStream = await response.Content.ReadAsStreamAsync();
        return await JsonSerializer.DeserializeAsync
            <IEnumerable<GitHubIssue>>(responseStream);
    }
}

也许这不是一个现实的例子，但是如何配置依赖注入来提供存储库名称？

Answer 1

我设法通过切换到命名客户端来完成这项工作：

//To start with, create a named client:
services.AddHttpClient("GitHubClient", ctx => { ctx.BaseAddress = new Uri("https://api.github.com/"); });

//Then set up DI for the TypedClient
services.AddTransient<IGitHubService>(ctx =>
{
    var clientFactory = ctx.GetRequiredService<IHttpClientFactory>();
    var httpClient = clientFactory.CreateClient("GitHubClient");
 
    return new GitHubService(httpClient, repositoryName);
});
  

Answer 2

如果您不想使用命名客户端，另一种方法是为额外参数创建自定义类。 因为问题是它不知道要为类型字符串解决什么问题，所以您可以做的是创建一个具有字符串属性的对象，该属性将包含您要传递的值，将其注册为单例并让容器解决它。

创建一个包含所有额外参数的类。在你的情况下“repositoryName”

public class RepositoryConfig
{
    public string RepositoryName {get; set;}
}

注册新班级

services.AddSingleton(new RepositoryConfig { RepositoryName = "MyRepo"});

然后注册HttpClient

services.AddHttpClient<IGitHubService, GitHubService>();

现在您的类将被正确实例化。

Answer 3

也许您可以通过HttpClients 属性传递参数。仓库名可以通过BaseAddress传递。

var repositoryName = // load from a config for example

services.AddHttpClient<GitHubService>(c =>
{
    c.BaseAddress = new Uri($"https://api.github.com/repos/aspnet/{repositoryName}");
    c.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json");
    c.DefaultRequestHeaders.Add("User-Agent", "HttpClientFactory-Sample");
});

Answer 4

如果您使用Autofac 作为依赖解析器，您可以使用Delegate Factories 实现此目的。

它看起来像这样

public delegate GitHubService GitHubServiceFactory(string repositoryName);

public class AnotherService
{
    private GitHubService gitHubService;
    public AnotherService(GitHubServiceFactory gitHubServiceFactory)
    {
        this.gitHubService = gitHubServiceFactory("myRepositoryName");
    }
}

据我所知，使用内置依赖解析器是不可能的。

Answer 5

正确的做法是使用AddHttpClient<TClient,TImplementation>(Func<HttpClient, IServiceProvider, TImplementation>)extension method:

services.AddHttpClient<IGitHubService, GitHubService>((client, sp) =>
    // any other constructor dependencies in GitHubService will be filled in
    // by ActivatorUtilities from the provided IServiceProvider
    ActivatorUtilities.CreateInstance<GitHubService>(sp, client, repositoryName)
);