在 IServiceCollection 扩展中获取服务 [英] Get a service in a IServiceCollection extension

问题描述

我有这个扩展

public static class ServiceCollectionExtensions
{
    public static IServiceCollection MyExtension(this IServiceCollection serviceCollection)
    {
      ...
    }
}

我需要从这样的服务中获取信息:

and I need to get information from a service like this:

services.AddAuthentication(options =>
    {
        options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
        options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
    })
    .AddJwtBearer(JwtBearerDefaults.AuthenticationScheme, options =>
    {
        var myService = <<HERE>>();
        options.TokenValidationParameters = this.GetTokenValidationParameters(myService);
    });

我该怎么做?

我试图在 var serviceProvider = services.BuildServiceProvider(); 之后获取 ServiceProvider 然后我发送了 serviceProvider，但这并没有不行..

I tried to get the ServiceProvider after var serviceProvider = services.BuildServiceProvider(); and then I send the serviceProvider, but this doesn't work..

推荐答案

在您调用 services.AddSomething() 时，服务 provider 尚未构建从服务集合呢.所以你不能在那个时候实例化一个服务.幸运的是，有一种方法可以在使用依赖注入的同时配置服务.

At the time you are calling services.AddSomething(), the service provider has not been built from the service collection yet. So you cannot instantiate a service at that time. Fortunately, there is a way to configure services while using dependency injection.

当你执行 services.AddSomething(options => ...) 时，通常会发生一定数量的服务将注册到服务集合中.然后传入的配置action也会以一种特殊的方式注册，这样当服务稍后被实例化时，它就能够执行那个配置操作以应用配置.

When you do services.AddSomething(options => …) what usually happens is that a certain amount of services will be registered with the service collection. And then the passed configuration action will also be registered in a special way, so that when the service is later instantiated, it will be able to execute that configuration action in order to apply the configuration.

为此，您需要实现 IConfigureOptions(或实际上 IConfigureNamedOptions 用于身份验证选项)并将其注册为单例.出于您的目的，这可能如下所示:

For that, you need to implement IConfigureOptions<TOptions> (or actually IConfigureNamedOptions<TOptions> for authentication options) and register it as a singleton. For your purpose, this could look like this:

public class ConfigureJwtBearerOptions : IConfigureNamedOptions<JwtBearerOptions>
{
    private readonly IMyService _myService;

    public ConfigureJwtBearerOptions(IMyService myService)
    {
        // ConfigureJwtBearerOptionsis constructed from DI, so we can inject anything here
        _myService = myService;
    }

    public void Configure(string name, JwtBearerOptions options)
    {
        // check that we are currently configuring the options for the correct scheme
        if (name == JwtBearerDefaults.AuthenticationScheme)
        {
            options.TokenValidationParameters = myService.GetTokenValidationParameters();
        }
    }

    public void Configure(JwtBearerOptions options)
    {
        // default case: no scheme name was specified
        Configure(string.Empty, options);
    }
}

然后您在 Startup 中注册该类型:

You then register that type in your Startup:

services.AddAuthentication(options =>
    {
        options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
        options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
    })
    // add JwtBearer but no need to pass options here
    .AddJwtBearer(JwtBearerDefaults.AuthenticationScheme, configureOptions: null);

// instead we are registering our configuration type to configure it later
services.AddSingleton<IConfigureOptions<JwtBearerOptions>, ConfigureJwtBearerOptions>();

这实际上和你只做 services.AddJwtBearer(scheme, options => { ... }) 时发生的完全一样，只是抽象出来的，所以你不需要关心关于它.但是通过手动操作，您现在可以拥有更多权力并访问完整的依赖注入服务提供者.

This is actually the exact same thing that happens when you just do services.AddJwtBearer(scheme, options => { … }), just abstracted away, so you don’t need to care about it. But by doing it manually, you now have more power and access to the full dependency injection service provider.

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