StructureMap IoC problem getting the instance in runtime

Question

i have 2 concrete types "CategoryFilter" & "StopWordsFilter" that implements "IWordTokensFilter".

Below is my setup:

ForRequestedType<IWordTokensFilter>().TheDefaultIsConcreteType<CategoryFilter>()
            .AddInstances(x =>
            {
                x.OfConcreteType<StopWordsFilter>();
            }
        );

The problem is the run-time when structure map auto inject it on my class, bec. i have arguments with same plugin-type:

public ClassA(IWordTokensFilter stopWordsFilter, IWordTokensFilter categoryFilter)

i'm always getting CategoryFilter in my first argument but it should be stopWordsFilter.

How can i setup this in a right way? thanks in advance

Answer 1

There are a number of possible solutions:

1) Does ClassA need to differentiate between the filters, or does it just need to run them both? If not, you can change the constructor to accept an array, which will cause all registered instances of IWordTokensFilter to be injected:

public ClassA(IWordTokensFilter[] filters)

You can then foreach over the filters to apply them.

2) If you do need to differentiate them, because they need to be used differently, you may consider having one implement a marker interface the better describes its purpose. ClassA could then be changed to take in an IWordTokensFilter and an ICategoryFilter (or whatever you name the marker interface). Register CategoryFilter with ICategoryFilter and then both will be injected properly.

public ClassA(IWordTokensFilter stopWordsFilter, ICategoryFilter categoryFilter)

3) You can tell StructureMap explicitly how to create ClassA:

ForRequestedType<ClassA>().TheDefault.Is.ConstructedBy(c => {
  return new ClassA(c.GetInstance<StopWordsFilter>(), c.GetInstance<CategoryFilter>());
});

4) You can tell StructureMap to override one of the dependencies for ClassA:

x.ForRequestedType<ClassA>().TheDefault.Is.OfConcreteType<ClassA>()
  .CtorDependency<IWordTokensFilter>("stopWordsFilter").Is<StopWordsFilter>();