给定一个ContainerBuilder，我可以注册一个缺少的依赖处理程序吗? [英] Given a ContainerBuilder, can I register a missing dependency handler?

问题描述

我正在尝试制作一种具有以下签名的方法:

I am trying to make a method with the following signature:

void Chain(ContainerBuilder builder, IServiceProvider fallbackServiceProvider)
{
   // ...
}

想法是 Chain 可以按以下方式使用:

The idea is that Chain can be used as follows:

IServiceProvider fallbackProvider = someExternalProvider;
var builder = new ContainerBuilder();

// Custom registration might happen before and/or after the call to Chain
builder.Register<MyCustomService>().As<IMyCustomService>();
builder.Register<MyExternalServiceReplacement>.As<IExternalService>();

Chain(builder, someExternalProvider);

IContainer container = builder.Build();

// customService should be a MyCustomService
var customService = container.Resolve<IMyCustomService>();

// replacedService should be overridden by MyExternalServiceReplacement
// even though an IExternalService also exists in someExternalProvider
var replacedService = container.Resolve<IExternalService>();

// nonReplacedService should come from someExternalProvider since
// no IExternalService2 was registered with the ContainerBuilder
var nonReplacedService = container.Resolve<IExternalService2>();

理想情况下，我可以向ContainerBuilder注册某种缺少的依赖处理程序.

Ideally there would be some type of missing dependency handler that I could register with the ContainerBuilder.

或者，我可能可以通过某种方式来注册一个组件，该组件可以拦截对 Resolve * ， TryResolve * 等的每次调用.需要拦截依赖项解析以进行构造函数注入.

Alternatively, I could probably get by with some way to register a component that could intercept every call to Resolve*, TryResolve*, etc... This would also need to intercept the dependency resolution for constructor injection.

不幸的是，无法查询IServiceProvider来获取它提供的每个服务.我只能调用 fallbackServicProvider 的 object IServiceProvider.GetService(Type serviceType)方法.

Unfortunately, there is no way to query the IServiceProvider to get every service it provides. I can only call into the object IServiceProvider.GetService(Type serviceType) method of the fallbackServicProvider.

推荐答案

您需要一个自定义的 IRegistrationSource 实现:当容器需要提供服务时，它将查询已注册的注册源以获取任何可用的实现.

You need a custom IRegistrationSource implementation: when the container needs to provide a service, it queries the registered registration sources to get any available implementations.

因此，在注册源中，您可以要求您的 IServiceProvider 为给定类型提供后备实现.

So inside the registeration source you can ask your IServiceProvider to give you a fallback implementation for a given type.

这是一篇很好的文章，介绍了Autofac中的整个注册来源:声明性Autofac 2中的上下文适配器

Here is a good article intoroducing the whole registration source in Autofac: Declarative Context Adapters in Autofac 2

基于这一点，我整理了一个原型 IRegistrationSource 实现(因此尚未经过全面测试，也没有生产准备就绪，但它已与您的示例场景一起使用)，这是什么?您可以基于:

Based on that I've knocked together a prototype IRegistrationSource implementation (so it is not fully tested nor production ready, but it was working with your sample scenario) what you can build on:

public class MyRegistrationSource : IRegistrationSource
{
    private readonly IServiceProvider serviceProvider;

    public MyRegistrationSource(IServiceProvider serviceProvider)
    {
        this.serviceProvider = serviceProvider;
    }

    public IEnumerable<IComponentRegistration> RegistrationsFor(Service service,
        Func<Service, IEnumerable<IComponentRegistration>> registrationAccessor)
    {
        // there are other registration exists in the container
        if (registrationAccessor(service).Any())
            return Enumerable.Empty<IComponentRegistration>();

        var swt = service as IServiceWithType;
        if (swt == null)
            return Enumerable.Empty<IComponentRegistration>();

        // try to get an instance from the IServiceProvider
        var instance = serviceProvider.GetService(swt.ServiceType);
        if (instance == null)
            return Enumerable.Empty<IComponentRegistration>();

        // register the instance in the container
        return new[]
            {
                RegistrationBuilder.ForDelegate(swt.ServiceType, 
                    (c, p) => instance)
                    .CreateRegistration()
            };
    }
    public bool IsAdapterForIndividualComponents { get { return false; } }
}

您可以像这样使用它:

 var builder = new ContainerBuilder();

 // Custom registration might happen before and/or after the call to Chain
 builder.RegisterType<MyCustomService>().As<IMyCustomService>();
 builder.RegisterType<MyExternalServiceReplacement>().As<IExternalService>();

 //Chain(builder, someExternalProvider);
 builder.RegisterSource(new MyRegistrationSource(new ServiceProvider()));

 IContainer container = builder.Build();

这篇关于给定一个ContainerBuilder，我可以注册一个缺少的依赖处理程序吗?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！