Question

I have the following class structure:

public class Fruit { }
public class Apple : Fruit { }

And then I am using a method from the .net framework that gets me a property value from a class returned as an object. So,

// values will be of type List<Apple>
object values = someObject.GetValue()

I now have this values object of type List and I want to cast it to a List of type Fruit. I tried the following but it didn’t work.

List<Fruit> fruits = values as List<Fruit>;

Anyone know how to go about casting an object to a List of its base class?

Update: At the point of casting I don’t know that the values object is of type List I just know that it should be a List of a type that inherits from Fruit.

Answer 1

The problem is that List<Apple> and List<Fruit> are not co-variant. You’ll first have to cast to List<Apple> and then use LINQ’s Cast method to cast the elements to Fruit:

List<Fruit> fruits = values is List<Apple> ? 
    (values as List<Apple>).Cast<Fruit>().ToList() :
    new List<Fruit>();

If you don’t know the type ahead of time and you don’t need to modify the list (and you’re using C# 4.0), you could try:

IEnumerable<Fruit> fruits = values as IEnumerable<Fruit>;

Or, I guess, if you need a List:

List<Fruit> fruits = (values as IEnumerable<Fruit>).ToList();