Using unity xml config to register an interface with nested generics

Question

If I have a class that implements a generic interface it works fine to configure it using the unity xml config.

public interface IReader<T> { }

public class Fund { }

public class FundReader : IReader<Fund> { }

and the unity xml:

<unity xmlns="http://schemas.microsoft.com/practices/2010/unity">
  <namespace name="System.ComponentModel" />
  <namespace name="TestUnityIssue" />
  <assembly name="TestUnityIssue" />
  <container>
    <register type="IReader[Fund]" mapTo="FundReader" />
  </container>
</unity>

And this works just using the following code:

var container = new UnityContainer().LoadConfiguration();
var fundReader = container.Resolve<IReader<Fund>>();

However, in some cases there is a wrapper around the type used in the reader. For example, adding the following two classes:

public class Wrapper<T> { }

public class WrappedFundReader : IReader<Wrapper<Fund>> { }

and if I add the following to the unity config:

<register type="IReader[Wrapper[Fund]]" mapTo="WrappedFundReader" />

and then try to resolve it using:

var wrappedReader = container.Resolve<IReader<Wrapper<Fund>>>();

I get the following exception:

InvalidOperationException - The current type,
TestUnityIssue.IReader`1[TestUnityIssue.Wrapper`1[TestUnityIssue.Fund]],
is an interface and cannot be constructed. Are you missing a type
mapping?

I can get around this by configuring it using code instead of xml:

container.RegisterType<IReader<Wrapper<Fund>>, WrappedFundReader>();

or I can create an interface that goes between and use that instead:

public interface IWrappedReader<T> : IReader<Wrapper<T>> { }

public class WrappedFundReader : IWrappedReader<Fund>

and the config would change to:

<register type="IWrappedReader[Fund]" mapTo="WrappedFundReader" />

It will still give me an instance that I can cast to IReader<Wrapper<Fund>>, but it seems like I should be able to make this work with the unity config.

What am I missing to make this work?

(If also tried creating specific aliases and wasn't able to get that to work either)

Answer 1

Aliasing worked for me...

<unity xmlns="http://schemas.microsoft.com/practices/2010/unity">
    <alias alias="WrappedFund" type="TestUnityIssue.Wrapper`1[[TestUnityIssue.Fund, TestUnityIssue, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]], TestUnityIssue, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
    <namespace name="TestUnityIssue" />
    <assembly name="TestUnityIssue" />
    <container>
        <register type="IReader[Fund]" mapTo="FundReader" />
        <register type="IReader[WrappedFund]" mapTo="WrappedFundReader" />
    </container>
</unity>

these both resolved...

var fundReader = container.Resolve<IReader<Fund>>();
var wrappedReader = container.Resolve<IReader<Wrapper<Fund>>>();

and depending on your situation, you may be able to get away with less than the full AssemblyQualifiedName...

<alias alias="WrappedFund" type="TestUnityIssue.Wrapper`1[[TestUnityIssue.Fund, TestUnityIssue]], TestUnityIssue" />