Checking for IEnumerable<T> with reflection

Question

EDIT

The bare-bones version of this question is, if I have some object o, how would I check to see if o is of some type that implements IEnumerable<string> with reflection? The original question is much more specific, but an answer to the above would be just as good. Sorry if I gave too much detail on this question

END EDIT

The following is a contrived ValueInjecter POC. Everything works well except for the isCollectionMapping method at the very bottom. I'm trying to get it to return true if and only if both the source and target property are any object that implement IEnumerable<respectiveTypes>.

I've tried IsAssignableFrom and also IsInstanceOfType, but neither seems to work.

Everything else works since when I uncomment the second line of the method to check explicitly for properties of name "Children", it works fine.

Note - I do know there are issues with this example. Namely, I'm trying to check for any old IEnumerable<> but yet always knowing enough to return List<>; it's just a silly proof of concept at this point.

[TestClass]
public class UnitTest1 {

    [TestMethod]
    public void TestMethod1() {
        List<string> strings = new List<string>();

        Subject S = new Subject() {
            id = 1,
            SubjectName = "S1",
            Children = { new Subject() { id = 2, SubjectName = "S1a" },
                         new Subject() { id = 3, SubjectName = "S1b", Children = { new Subject() { id = 4} } } }
        };

        SubjectViewModel VM = (SubjectViewModel)new SubjectViewModel().InjectFrom<CollectionToCollection>(S); ;


        Assert.AreEqual(2, VM.Children.Count);
        Assert.AreEqual(1, VM.Children.Single(s => s.id == 3).Children.Count);
    }
}


public class Subject {
    public Subject() {
        Children = new List<Subject>();
    }

    public string SubjectName { get; set; }
    public int id { get; set; }

    public List<Subject> Children { get; set; }
}

public class SubjectViewModel {
    public SubjectViewModel() {
        Children = new List<SubjectViewModel>();
    }

    public string SubjectName { get; set; }
    public int id { get; set; }

    public List<SubjectViewModel> Children { get; set; }
}

public class CollectionToCollection : Omu.ValueInjecter.ConventionInjection {
    protected override bool Match(ConventionInfo c) {
        return c.TargetProp.Name == c.SourceProp.Name;
    }

    protected override object SetValue(ConventionInfo c) {
        if (isCollectionMapping(c))
            return (c.SourceProp.Value as IEnumerable<Subject>).Select(s => (SubjectViewModel)(new SubjectViewModel().InjectFrom<CollectionToCollection>(s))).ToList();
        else
            return c.SourceProp.Value;
    }

    private bool isCollectionMapping(ConventionInfo c) {
        return c.SourceProp.Value.GetType().IsInstanceOfType(typeof(IEnumerable<Subject>)) && c.TargetProp.Value.GetType().IsAssignableFrom(typeof(IEnumerable<SubjectViewModel>));

        //return c.SourceProp.Name == "Children" && c.TargetProp.Name == "Children";
    }
}

Answer 1

If I have some object o, how would I check to see if o is of some type that implements IEnumerable<string>?

As simple as:

o is IEnumerable<string>

By the way, your current code isn't working because it is reversing the testing of the assignability relationship (as though the method were called IsAssignableTo), i.e. It is assuming that:

Bar bar = ...
Foo foo = bar

implies:

typeof(Bar).IsAssignableFrom(typeof(Foo)) // wrong

In reality, the actual implication is that:

typeof(Foo).IsAssignableFrom(typeof(Bar))

Namely, I'm trying to check for any old IEnumerable<>:

In this case, you need to test if the type implements a constructed version of the generic interface:

o.GetType()
 .GetInterfaces()
 .Any(t => t.IsGenericType 
        && t.GetGenericTypeDefinition() == typeof(IEnumerable<>))

Answer 2

The bare-bones version of this question is, if I have some object o, how would I check to see if o is of some type that implements IEnumerable<string>?

Like this:

object o = whatever;
bool isSequenceOfStrings = o is IEnumerable<string>;

Answer 3

I could have missed something (didn't read your whole code sample), but it doesn't seem like you need reflection here.

How about just using:

if (c.SourceProp.Value is IEnumerable<Subject>)
   return true;

If you don't know the specific type, use generics:

public bool MyFunction<T>(...)
{
   if (c.SourceProp.Value is IEnumerable<T>)
      return true;
}

Or if you need to use the interface, do it this way (saves a cast):

var enumerable = c.SourceProp.Value as IEnumerable<string>;
if (enumerable != null)
{
   // Use IEnumerable<string>
   return true;
}

return false;