具有同一接口的多种实现的Autofac [英] Autofac with multiple implementations of the same interface

问题描述

我正在使用Autofac，并且希望有一个接口的多个实现.如何配置Autofac，以便根据当前类型解析依赖关系?

I'm using Autofac and would like to have multiple implementations of an interface. How can I configure Autofac so to resolve dependencies based on the current type?

更具体地说，我有一个接口和应该链接在一起的多个实现.

More specifically, I have one interface and multiple implementations that should be chained together.

让我解释一下(虚拟课):

Let me explain (fictitious classes):

public interface IMessageHandler
{
    void Handle(Message message);
}

public class LoggingMessageHandler : IMessageHandler
{
    private IMessageHandler _messageHandler;

    public LoggingMessageHandler(IMessageHandler messageHandler)
    {
        _messageHandler = messageHandler;
    }

    public void Handle(Message message) 
    {
        // log something
        _messageHandler.Handle(message);
    }
}

public class DoSomethingMessageHandler : IMessageHandler
{
    private IMessageHandler _messageHandler;

    public DoSomethingMessageHandler (IMessageHandler messageHandler)
    {
        _messageHandler = messageHandler;
    }

    public void Handle(Message message) 
    {
        // do something
        _messageHandler.Handle(message);
    }
}

在链的底部可能是一个IMessageHandler，它不会将消息传递给下一个消息.

At the bottom of the chain might be an IMessageHandler that doesn't pass the message on to the next one.

如果我想要以下链:

TopLevelClass -> LoggingMessageHandler -> DoSomethingMessageHandler -> FinalHandler

如何告诉Autofac

How can I tell Autofac to

• 将LoggingMessageHandler传递给TopLevelClass(以实现对IMessageHandler的依赖)
• 将DoSomethingMessageHandler传递给LoggingMessageHandler(以实现对IMessageHandler的依赖)
• 将LoggingMessageHandler传递给FinalHandler(以实现对IMessageHandler的依赖)

• pass LoggingMessageHandler to TopLevelClass (to fulfill its dependency on IMessageHandler)
• pass DoSomethingMessageHandler to LoggingMessageHandler (to fulfill its dependency on IMessageHandler)
• pass LoggingMessageHandler to FinalHandler (to fulfill its dependency on IMessageHandler)

是否有可能(我已经阅读了对IEnumerable的隐式支持) ?还是我必须在两者之间使用额外的类(工厂之类的东西)?

Is it even possible (I have read about the implicit support for IEnumerable)? Or will I have to use an extra class in between (a factory or something)?

推荐答案

此处有4个选项: https://autofaccn.readthedocs.io/en/latest/faq/select-by-context.html

选项1:重新设计界面

ILoggingMessageHandler , IDoSomethingMessageHandler 

选项2:更改注册

builder.Register(ctx => new FinalHandler(ctx.Resolve<LoggingMessageHandler >()));
or
builder.Register(ctx => new FinalHandler(ctx.Resolve<IDoSomethingMessageHandler >()));

选项3:使用键控服务

builder.RegisterType<FinalHandler>()
           .WithParameter(
             new ResolvedParameter(
               (pi, ctx) => pi.ParameterType == typeof(IMessageHandler),
               (pi, ctx) => ctx.ResolveKeyed<ISender>("something")));

选项4:使用元数据

public class FinalHandler
{
  public FinalHandler([WithMetadata("sendBy", "something")] IMessageHandler messageHandler) { ... }
}

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