CODEWITHSUNDEEP
c#.net
Matthew Layton
Matthew Layton

Reputation: 42260

How to determine if an object implements IDictionary or IList of any type

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?

Upvotes: 5

Views: 4240

Answers (4)

Timothy C. Quinn
Timothy C. Quinn

Reputation: 4485

Here is some boolean functions that work with generic interface types in vb.net framework 2.0:

Public Shared Function isList(o as Object) as Boolean
    if o is Nothing then return False
    Dim t as Type = o.GetType()
    if not t.isGenericType then return False
    return (t.GetGenericTypeDefinition().toString() = "System.Collections.Generic.List`1[T]")
End Function

Public Shared Function isDict(o as Object) as Boolean
    if o is Nothing then return False
    Dim t as Type = o.GetType()
    if not t.isGenericType then return False
    return (t.GetGenericTypeDefinition().toString() = "System.Collections.Generic.Dictionary`2[TKey,TValue]")
End Function

Upvotes: 0

Jay
Jay

Reputation: 57919

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.

Upvotes: 4

AshMeth
AshMeth

Reputation: 99

    private void CheckType(object o)
    {
        if (o is IDictionary)
        {
            Debug.WriteLine("I implement IDictionary");
        }
        else if (o is IList)
        {
            Debug.WriteLine("I implement IList");
        }
    }

Upvotes: 9

LukeHennerley
LukeHennerley

Reputation: 6434

Not sure if this is what you'd want but you could use the GetInterfaces on the item type and then see if any of the returned list are IDictionary or IList

item.GetType().GetInterfaces().Any(x => x.Name == "IDictionary" || x.Name == "IList")

That should do it I think.

Upvotes: 1

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