autofac registration issue in release v2.4.5.724

问题

I have the following registration

builder.Register<Func<Type, IRequestHandler>>(
          c => request => (IRequestHandler)c.Resolve(request));

Basically I am trying to register a factory method that resolves an instance of IRequestHandler from a given type.

This works fine until the version 2.4.3.700. But now I am getting a the following error..

Cannot access a disposed object. Object name: 'This resolve operation has already ended. When registering components using lambdas, the IComponentContext 'c' parameter to the lambda cannot be stored. Instead, either resolve IComponentContext again from 'c', or resolve a Func<> based factory to create subsequent components from.'.

UPDATE

I was trying to limit autofac's exposure to the rest of the projects in the solution. Nick, thanks for the hint, now my registration looks like this...

 builder.Register<Func<Type,IRequestHandler>>(c =>  
         { 
           var handlers = c.Resolve<IIndex<Type,RequestHandler>>(); 
           return  request => handlers[request];  
         });

回答1:

The c in this expression is a temporary, so this code while previously functional, is broken. Autofac 2.4.5 detects this problem while earlier versions silently ignored it.

To fix the issue, explicitly resolve IComponentContext:

builder.Register<Func<Type, IRequestHandler>>(c => {
    var ctx = c.Resolve<IComponentContext>();
    return request => (IRequestHandler)ctx.Resolve(request));
});

The functionality you're emulating here might be better represented using keys and indexes, e.g. see Interrupted chain of IoC or http://code.google.com/p/autofac/wiki/TypedNamedAndKeyedServices.

回答2:

I had a similar problem as the user6130. I wanted to avoid using IIndex in my class implementation and pass in a service resolver into my constructor instead.

So now I have my service implementation with the following constructor:

public MvcMailer(Converter<string, MailerBase> mailerResolver)
{
     _resolver = mailerResolver;
}

I wanted to used keyed services without directly relying on the Autofac namespace. I was getting the same error until I restructured the configuration as such.

1) Scan for all my mailer implementations and index via class name (could be improved)

builder.RegisterAssemblyTypes(System.Reflection.Assembly.GetExecutingAssembly())
       .Where(t => t.Name.EndsWith("Mailer")).Keyed<Mvc.Mailer.MailerBase>(t => t.Name.Replace("Mailer", "").ToLower());

2) Register the converter in Autofac config

builder.Register<System.Converter<string,Mvc.Mailer.MailerBase>>(c =>  {
    var all = c.Resolve<Autofac.Features.Indexed.IIndex<string,Mvc.Mailer.MailerBase>>();
         return delegate(string key)
         {
              return all[key];
         };
     });

3) Register like other types of components and let Autofac handle the Converter injection

builder.RegisterType<Mailers.MvcMailer>().As<Mailers.IMailer>();

来源：https://stackoverflow.com/questions/5383888/autofac-registration-issue-in-release-v2-4-5-724

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autofac