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 might be bound to a dictionary, but this isn't known at compile time.

I would like to do something similar to this:

if (listBox.ItemsSource is Dictionary<??>)
{
    KeyValuePair<??> pair = (KeyValuePair<??>)listBox.SelectedItem;
    object value = pair.Value;
}

Is there a way to do this dynamically at runtime using reflection? I know it's possible to use reflection with generic types and determine the key/value parameters, but I'm not sure if there's a way to do the rest after those values are retrieved.

Answer 1

Check to see if it implements IDictionary.

See the definition of System.Collections.IDictionary to see what that gives you.

if (listBox.ItemsSource is IDictionary)
{
    DictionaryEntry pair = (DictionaryEntry)listBox.SelectedItem;
    object value = pair.Value;
}

EDIT: Alternative when I realized KeyValuePair's aren't castable to DictionaryEntry

if (listBox.DataSource is IDictionary)
{
     listBox.ValueMember = "Value";
     object value = listBox.SelectedValue;
     listBox.ValueMember = ""; //If you need it to generally be empty.
}

This solution uses reflection, but in this case you don't have to do the grunt work, ListBox does it for you. Also if you generally have dictionaries as data sources you may be able to avoid reseting ValueMember all of the time.

Answer 2

You could be a little more generic and ask instead if it implements IDictionary. Then the KeyValue collection will contina plain Objects.

Answer 3

you can check to see if it implements IDictionary. You'll just have to enumerate over using the DictionaryEntry class.

Answer 4

It should be something like the following. I wrote this in the answer box so the syntax may not be exactly right, but I've made it Wiki editable so anybody can fix up.

if (listBox.ItemsSource.IsGenericType && 
    typeof(IDictionary<,>).IsAssignableFrom(listBox.ItemsSource.GetGenericTypeDefinition()))
{
    var method = typeof(KeyValuePair<,>).GetProperty("Value").GetGetMethod();
    var item = method.Invoke(listBox.SelectedItem, null);
}

Answer 5

I think you could do:

if(listBox.ItemSource.GetType().Equals(new Dictionary().GetType()))
{
   //do something
}

Answer 6

I believe a warning is at place.

When you're testing if an object 'is a' something this or that, you're reimplementing (part of) the type system. The first 'is a' is often swiftly followed by a second one, and soon your code is full of type checks, which ought to be very well handled by the type system - at least in an object oriented design.

Of course, I know nothing of the context of the question. I do know a 2000 line file in our own codebase that handles 50 different object to String conversions... :(

Answer 7

if(typeof(IDictionary).IsAssignableFrom(listBox.ItemsSource.GetType()))
{

}