Find implementation of generic interface

Question

I am registering classes dynamically from an assembly, a bunch of command handlers:

class class DummyCommand : ICommand {}

class GetAgeCommandHandler : ICommandHandler<DummyCommand>
{
    public void Handle(DummyCommand command) { }
}

I have code which lists all types that implement the generic interface, in this case i am interested in ICommandHandler<> interfaces with the below helper method:

public static IEnumerable<Type> GetAllTypesImplementingOpenGenericType(this Assembly assembly, Type openGenericType)
{
    return from x in assembly.GetTypes()
            from z in x.GetInterfaces()
            let y = x.BaseType
            where
            (y != null && y.IsGenericType &&
            openGenericType.IsAssignableFrom(y.GetGenericTypeDefinition())) ||
            (z.IsGenericType &&
            openGenericType.IsAssignableFrom(z.GetGenericTypeDefinition()))
            select x;
}

With the below registration code:

var assemblies = AppDomain.CurrentDomain.GetAssemblies();
foreach (var implementation in assembly.GetAllTypesImplementingOpenGenericType(typeof(ICommandHandler<>)))
{
    // below is wrong, i cannot get the generic type it is empty
    // var commandType = implementation.UnderlyingSystemType.GenericTypeArguments[0];
    // what should i put to find the type `DummyCommand`

    // registeration would be below
    var handlerType = (typeof(ICommandHandler<>)).MakeGenericType(commandType);
    container.Register(handlerType, implementation);
}

Basically i am trying to register with the SimpleInjector container (but could be any ioc container) the type container.Register(typeof(ICommandHandler<DummyCommand>), typeof(GetAgeCommandHandler)) but with generics at runtime, i need to also be careful to handle cases where a class implements multiple ICommandHandler interfaces (of different command types).

Pointers much appreciated.

Answer 1

您可能有兴趣阅读Simple Injector的有关进行自动注册的精美手册 ，因为发布的代码块可以简化为简单的单行代码：

container.Register(typeof(ICommandHandler<>), AppDomain.CurrentDomain.GetAssemblies());