具有WebForms公共属性的Autofac引发构造函数异常

Question

I am trying to modify an existing WebForms application and would like to use Autofac. As far as I can tell, I've set up the application according to the documentation ( http://autofac.readthedocs.org/en/latest/integration/webforms.html#structuring-pages-and-user-controls-for-di ).

Web page code with a public property

public partial class MyTestPage : Page
{
    public ILogger Logger { get; set; }

    protected void Page_Load(object sender, EventArgs e)
    {
        //page load code here

web.config

<modules>
<add name="ContainerDisposal" type="Autofac.Integration.Web.ContainerDisposalModule, Autofac.Integration.Web" preCondition="managedHandler" />
  <add name="PropertyInjection" type="Autofac.Integration.Web.Forms.PropertyInjectionModule, Autofac.Integration.Web" preCondition="managedHandler" />
</modules>          

Global.asax.cs

public class Global : HttpApplication, IContainerProviderAccessor
{
        static IContainerProvider _containerProvider;

        public IContainerProvider ContainerProvider
        {
            get { return _containerProvider; }
        }


    void Application_Start(object sender, EventArgs e)
    {
        var builder = new ContainerBuilder();
        builder.RegisterType<Logger>().As<ILogger>().InstancePerRequest();
        _containerProvider = new ContainerProvider(builder.Build());

    }

When I try to load the page, Autofac throws this exception.

No constructors on type 'NLog.Logger' can be found with the constructor finder 'Autofac.Core.Activators.Reflection.DefaultConstructorFinder'.

What am I missing here? Why is Autofac looking for a constructor instead of picking up the public property?

Answer 1

The problem here is that Autofac is trying to create an instance of Logger class to inject it to your MyTestPage . It tries using default, parameter-less constructor, which is unavailable. So the problem is not with your page, but with your logger registration.

I am not familiar to NLog , but according to tutorial, you are suppose to use LogManager to create instances of Logger , eg

Logger logger = LogManager.GetCurrentClassLogger();

or

Logger logger = LogManager.GetLogger("MyClassName");

So you should change your registration to something like this (not tested):

builder.Register(c => LogManager.GetCurrentClassLogger()).As<ILogger>().InstancePerRequest();

As I mentioned above, I am not familiar with NLog, but I assume NLog Logger class implements ILogger interface.

EDIT:

This module should handle what you are trying to achieve.