Autofac Scanning Assemblies for certain class type

Question

I've started using Autofac and want to scan some DLL's and get Autofac to register some of the classes within them.

The classes that I'm interested in all inherit from a PluginBase class but the below code doesn't seem to be registering them. Can anyone help?

        var assemblies = AppDomain.CurrentDomain.GetAssemblies();


        var builder = new ContainerBuilder();
        builder.RegisterAssemblyTypes(assemblies)
            .Where(t => t.BaseType == typeof(PluginBase))
            .AsImplementedInterfaces()
            .AsSelf();

        var container = builder.Build();
        var pluginClasses = container.Resolve<IEnumerable<PluginBase>>();

        //pluginClasses is empty!!!!

Solution 1

I think you need to specify the base class of your Plugins on registration. The call AsImplementedInterfaces registers the type with its implemented interfaces and not by its base type. You should update your registration to register your plugins as PluginBase.

Here´s the code:

var assemblies = AppDomain.CurrentDomain.GetAssemblies();


    var builder = new ContainerBuilder();
    builder.RegisterAssemblyTypes(assemblies)
        .Where(t => t.BaseType == typeof(PluginBase))
        .As<PluginBase>();

    var container = builder.Build();
    var pluginClasses = container.Resolve<IEnumerable<PluginBase>>();

Solution 2

Maybe do is this way:

builder
    .RegisterAssemblyTypes(AppDomain.CurrentDomain.GetAssemblies())
    .Where(t => t.GetInterfaces()
        .Any(i => i.IsAssignableFrom(typeof (IDependency))))
    .AsImplementedInterfaces()
    .InstancePerDependency();

In this code I use IDependency as a marker interface. You may replace it with your PluginBase class and remove Where method.

The point is to use IsAssignableFrom method.

Comments

[Jon]

Will that allow for classes that don't implement interfaces and those that do? I'm working with legacy code so old stuff wont have interfaces but new stuff will

[Wojteq]

It should work with Where(t => t.IsAssignableFrom(typeof(PluginBase)). If not, I'll try to help you.

[Wojteq]

Of course remove .AsImplementedInterfaces(). I didn't notice this line.

[Jon]

That doesn't work either. PluginBase is abstract if that helps

[Jon]

If I put my original code back and just take out the where clause it works

[Jon]

That works! Could I add the AsImplementedInterfaces for newer classes that do implement interfaces?

[Wojteq]

Are the classes that extends PluginBase in your current AppDomain?

[Jehof]

I think these two calls should work together. Then the type gets registered with by its base type and all interfaces it implements.

[Jon]

Oops, just re-read what I wrote and doesn't make sense. If I have a class that inherits from PluginBase and has a constructor argument of an interface this won't work even with AsImplementedInterfaces. Do I do a new builder registration or can I amend the current code?

[Jon]

Yes they are. Jehof's seems to be getting somewhere but I still stuck

[Jon]

I just got it working by calling RegisterAssemblyTypes again. Thanks for your help.

[Nicholas Blumhardt]

Just a note, you don't need the Where call if you use As.

[Omer Faruk Zorlu]

That does not works when assembly are not loaded. AppDomain.CurrentDomain.GetAssemblies is only returns loaded assemblies.