Autofac装饰器+代表工厂 [英] Autofac decorator + delegate factory

问题描述

我试图在Autofac中使用带有委托工厂的装饰器，但是我似乎无法通过它来解析参数.

I am trying to use a decorator in Autofac with a delegate factory but I can't seem to get it to resolve the parameters.

public interface IFoo
{ }

public class Foo : IFoo
{
    public Foo(string bar)
    { ... }
}

public class DecoratedFoo : IFoo
{
    public DecoratedFoo(IFoo decorated)
    { ... }
}

我想注入这样的服务:

public SomeService(Func<string, IFoo> factory)
{
    // I would expect IFoo to be a DecoratedFoo here
    IFoo foo = factory("hello");
}

我已经注册了以下组件:

I have registered components like so:

builder.RegisterType<Foo>()
    .Named<IFoo>("foo")
    .UsingConstructor(typeof(string));

builder.RegisterDecorator<IFoo>(
    (ctx, inner) => new DecoratedFoo(inner),
    fromKey: "foo");

我收到一条错误消息，提示它无法解析我的参数栏.这是一个简化的示例，但我不知道bar的值是什么(因此使用工厂).

I get an error saying it cannot resolve my parameter bar. This is a simplified example but I won't know what the value of bar is (hence using the factory).

有什么方法可以完成我的工作吗?

Is there any way to accomplish what I'm doing?

推荐答案

使用RegisterDecorator时-它不会传播字符串参数，您将传递给工厂的更深的Foo构造函数.这是有关此问题的公开问题.所以在这行上

When you use RegisterDecorator - it will not propagate string parameter you pass to your factory deeper to your Foo constructor. Here is an open issue about that. So on this line

IFoo foo = factory("hello");

它将抛出异常(如您所观察到的)，因为它将尝试查找Foo的无参数构造函数，并且没有.

It will throw exception (as you observe) because it will try to find parameterless constructor of Foo and there is none.

要解决此问题，您可以删除您的RegisterDecorator，而改为手动进行:

To fix, you can remove your RegisterDecorator and instead do that manually:

builder.RegisterType<Foo>()
    .Named<IFoo>("foo");            
builder.Register((cnt, parameters) => 
    new DecoratedFoo(cnt.ResolveNamed<IFoo>("foo", parameters))).As<IFoo>();  

几乎相同数量的代码，但是可以正常工作，因为您可以手动传播参数.

Almost the same amount of code, but works as expected, because you manually propagate parameters.

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