Question

How do you get a collection of all the types that inherit from a specific other type?

Answer 1

Something like:

public IEnumerable<Type> FindDerivedTypes(Assembly assembly, Type baseType)
{
    return assembly.GetTypes().Where(t => baseType.IsAssignableFrom(t));
}

If you need to handle generics, that gets somewhat trickier (e.g. passing in the open List<> type but expecting to get back a type which derived from List<int>). Otherwise it’s simple though 🙂

If you want to exclude the type itself, you can do so easily enough:

public IEnumerable<Type> FindDerivedTypes(Assembly assembly, Type baseType)
{
    return assembly.GetTypes().Where(t => t != baseType && 
                                          baseType.IsAssignableFrom(t));
}

Note that this will also allow you to specify an interface and find all the types which implement it, rather than just working with classes as Type.IsSubclassOf does.