c# - How do I cast a List<T> effectively?

Question

I have a

List<InputField> 

but I need a

List<IDataField>  

Is there a way to cast this in c#? Or use Linq to get same result?

I have two classes that implement the same interface:

interface IDataField { }
class InputField : IDataField { }
class PurchaseField : IDataField { }

This List comes from a Linq-to-Sql query:

List<InputField> list = (from i .... select i).ToList();

Answer 1

Both .OfType<T> and .Cast<T> will return a list of T, but the meaning of the two methods is different.

list.OfType() filters the original list and returns all items which are of type T, and skips the ones that are not of that type.

list.Cast() casts all items in the original list to type T, and throws an exception for items which cannot be cast to that type.

In your case both would give the same result, but using .Cast() would communicate your intent a lot more clearly, so I would recommend using that.

List<InputField> list = (from i .... select i).Cast<IDataField>().ToList();