IAutofacActionFilter injecting a logger

问题

I'm using NLog with this module:

public class LoggingModule : Autofac.Module
{
    protected override void AttachToComponentRegistration(IComponentRegistry componentRegistry, IComponentRegistration registration)
    {
        registration.Preparing += OnComponentPreparing;
        registration.Activated += (sender, e) => InjectLoggerProperties(e.Instance);
    }

    private static void OnComponentPreparing(object sender, PreparingEventArgs e)
    {
        var t = e.Component.Activator.LimitType;
        e.Parameters = e.Parameters.Union(
            new[]
            {
                new ResolvedParameter((p, i) => IsLogger(p), (p, i) => GetLogger(t.FullName))
            });
    }

    private static void InjectLoggerProperties(object instance)
    {
        var instanceType = instance.GetType();

        var properties = instanceType
            .GetProperties(BindingFlags.Public | BindingFlags.Instance)
            .Where(p => IsLogger(p) && p.CanWrite && p.GetIndexParameters().Length == 0);

        foreach (var propToSet in properties)
        {
            propToSet.SetValue(instance, GetLogger(instanceType.FullName), null);
        }
    }

    private static ILogger GetLogger(string name)
    {
        return LogManager.GetLogger(name);
    }

    private static bool IsLogger(ParameterInfo p)
    {
        return p.ParameterType == typeof (ILogger);
    }

    private static bool IsLogger(PropertyInfo p)
    {
        return p.PropertyType == typeof(ILogger);
    }
}

Everything seems to work fine, except the logger's name is empty/wrong. On the first line of OnComponentPreparing, the LimitType is a Meta<Lazy<IAutofacActionFilter>>[] instead of the expected LogControllerActionFilterAttribute. How do I get the correct type name for the logger? In my logs, this is given as the logger name:

0, Culture=neutral, PublicKeyToken=b77a5c561934e089]][]

Edit:

This is a short and complete program demonstrating this issue. You'll need the module implementation above as well.

internal class Program
{
    private static void Main(string[] args)
    {
        var builder = new ContainerBuilder();
        builder.RegisterModule<LoggingModule>();
        builder.RegisterType<Foo>().As<IFoo>();

        var container = builder.Build();

        // This prints out "0, Culture=neutral, PublicKeyToken=b77a5c561934e089]][]" for the logger name
        foreach (var metalazyfoo in container.Resolve<Meta<Lazy<IFoo>>[]>())
            metalazyfoo.Value.Value.Work(5);

        // This prints out "Foo" for the logger name
        container.Resolve<Meta<Lazy<IFoo>>>().Value.Value.Work(6);

        Console.WriteLine("=== Done ===");
        Console.ReadLine();
    }
}


public class Foo : IFoo
{
    private readonly Logger _logger;

    public Foo(Logger logger)
    {
        _logger = logger;
    }

    public void Work(int x)
    {
        _logger.Debug(x);
    }
}

public interface IFoo
{
    void Work(int x);
}

回答1:

Here LimitType should be

var t = e.Component.Target.Activator.LimitType;

Instead of

var t = e.Component.Activator.LimitType;

This is to avoid creating loggers with the type of the activator, not the type of the underlying component being activated. Which is why you're getting the Meta>[] instead of LogControllerActionFilterAttribute.

来源：https://stackoverflow.com/questions/30086194/iautofacactionfilter-injecting-a-logger