Testing if an Object is a Dictionary in C#

Question

Is there a way to test if an object is a dictionary?

In a method I\'m trying to get a value from a selected item in a list box. In some circumstances, the list box

Answer 1

I know this question was asked many years ago, but it is still visible publicly.

There were few examples proposed here in this topic and in this one:
Determine if type is dictionary [duplicate]

but there are few mismatches, so I want to share my solution

Short answer:

var dictionaryInterfaces = new[]
{
    typeof(IDictionary<,>),
    typeof(IDictionary),
    typeof(IReadOnlyDictionary<,>),
};

var dictionaries = collectionOfAnyTypeObjects
    .Where(d => d.GetType().GetInterfaces()
        .Any(t=> dictionaryInterfaces
            .Any(i=> i == t || t.IsGenericType && i == t.GetGenericTypeDefinition())))

Longer answer:
I believe this is the reason why people make mistakes:

//notice the difference between IDictionary (interface) and Dictionary (class)
typeof(IDictionary<,>).IsAssignableFrom(typeof(IDictionary<,>)) // true 
typeof(IDictionary).IsAssignableFrom(typeof(IDictionary)); // true

typeof(IDictionary).IsAssignableFrom(typeof(Dictionary)); // true
typeof(IDictionary<,>).IsAssignableFrom(typeof(Dictionary<,>)); // false!! in contrast with above line this is little bit unintuitive

so let say we have these types:

public class CustomReadOnlyDictionary : IReadOnlyDictionary
public class CustomGenericDictionary : IDictionary
public class CustomDictionary : IDictionary

and these instances:

var dictionaries = new object[]
{
    new Dictionary(),
    new ReadOnlyDictionary(new Dictionary()),
    new CustomReadOnlyDictionary(),
    new CustomDictionary(),
    new CustomGenericDictionary()
};

so if we will use .IsAssignableFrom() method:

var dictionaries2 = dictionaries.Where(d =>
    {
        var type = d.GetType();
        return type.IsGenericType && typeof(IDictionary<,>).IsAssignableFrom(type.GetGenericTypeDefinition());
    }); // count == 0!!

we will not get any instance

so best way is to get all interfaces and check if any of them is dictionary interface:

var dictionaryInterfaces = new[]
{
    typeof(IDictionary<,>),
    typeof(IDictionary),
    typeof(IReadOnlyDictionary<,>),
};

var dictionaries2 = dictionaries
    .Where(d => d.GetType().GetInterfaces()
        .Any(t=> dictionaryInterfaces
            .Any(i=> i == t || t.IsGenericType && i == t.GetGenericTypeDefinition()))) // count == 5