Question

Lets say I declare the following

Dictionary<string, string> strings = new Dictionary<string, string>();
List<string> moreStrings = new List<string>();

public void DoSomething(object item)
{
   //here i need to know if item is IDictionary of any type or IList of any type.
}

I have tried using:

item is IDictionary<object, object>
item is IDictionary<dynamic, dynamic>

item.GetType().IsAssignableFrom(typeof(IDictionary<object, object>))
item.GetType().IsAssignableFrom(typeof(IDictionary<dynamic, dynamic>))

item is IList<object>
item is IList<dynamic>

item.GetType().IsAssignableFrom(typeof(IList<object>))
item.GetType().IsAssignableFrom(typeof(IList<dynamic>))

All of which return false!

So how do i determine that (in this context) item implements IDictionary or IList?

Answer 1

You can use the non-generic interface types, or if you really need to know that the collection is generic you can use typeof without type arguments.

obj.GetType().GetGenericTypeDefinition() == typeof(IList<>)
obj.GetType().GetGenericTypeDefinition() == typeof(IDictionary<,>)

For good measure, you should check obj.GetType().IsGenericType to avoid an InvalidOperationException for non-generic types.