Can I get the item type from a BindingSource?

Question

I would like to get the Type of item that a BindingSource is hooked up to or configured for. The BindingSource.DataSource property can be set to an object, list, or type. If it is a Type, it obviously does not have a bound item yet, but I would still like to get the Type. For a List, I need the item Type, not the list type.

I currently have a custom list type for business objects that implement an IListItemType interface, that I created to solve this problem a while back. I would now like to get this working in a more generic fashion so that it will work with any list.

I've looked through the API docs for for a good way to do this, but so far I have not had any luck. Am I missing something or is this just something I can not or should not be doing?

Answer 1

There is no completely generic way to get the "type" of the list. The most common method is to examine the first item, but this can be misleading as you can have objects that are of a more specific type in a collection that is less specific (in other words, the collection might be a List<object>, but the first item might be a string, leading you to guess that it's a List<string>). If you're confident that all of the elements will be the same type (meaning none are more specific than the generic type of the collection or than any of the other objects), then examining the first item is the easiest.

Apart from that, you could examine the list's actual type using GetType and check its interfaces. Chances are that any collection that's strongly typed is going to implement IEnumerable<T>, so you can iterate over its interfaces looking for IEnumerable that's generic, then look at its generic type arguments. It's (more than) a little hokey, but it should work.

TL;DR Version

Try this. Assuming you're using .NET 3.5 and have the list stored in a variable called list:

var listType = list.GetType().GetInterfaces()
              .Where(t => t.Name == "IEnumerable" && t.IsGenericType)
              .Select(t => t.GetGenericArguments()[0]).FirstOrDefault();

As long as the list implements IEnumerable<T>, this will give you T. If it doesn't, chances are the list type is object anyway.

Answer 2

I recently ran accross this in the framework.

System.Windows.Forms.ListBindingHelper.GetListItemType() and GetListItemProperties()

This class has everything I was looking for.