List.Cast<> error "is a method which is not valid in the given context"
c#, casting, linq
Solution
In lieu of actually seeing your code so we can fix it, how about changing the method instead:
public void DoSomething<T>(IEnumerable<T> items) where T : ParentType
{
...
}
Or if you're using C# 4 and .NET 4, this should be fine, as `IEnumerable<T>` is covariant in `T` in .NET 4.
public void DoSomething(IEnumerable<ParentType> items)
{
...
}
Do you really need the method to accept a `List<ParentType>`? After all, if you're going to call:
var parentList = childList.Cast<ParentType>().ToList();
and pass that into the method, then you've got two entirely separate lists by that point anyway.
By the way, another effect of the covariant of `IEnumerable<T>` is that in .NET 4 you can avoid the `Cast` call and just call:
var parentList = childList.ToList<ParentType>();
EDIT: Now that you've posted your code, it's simply a matter of not calling the `Cast` method as a method:
// This...
helper(listB.Cast<P>.ToList())
// should be this:
helper(listB.Cast<P>().ToList())
Problem
I have an abstract parent class which child classes that inherit from it. I have another class that contains many `List<>` types of the different child classes. I then have a method in another class that takes a parameter of `List<ParentType>` and just calls the methods that are declared abstract. I'm having a problem using `List<T>.Cast<T2>` on the lists of the child classes. I'm getting the error: System.Linq.Enumerable.Cast(System.Collections.IEnumerable)' is a 'method', which is not valid in the given context Does anybody know how to fix this error? Or do I have to reconstruct a list of type `List<ParentType>` and recast each item individually? What I'm trying to do: public abstract class P { public int num; public abstract double addSections(); } ``` public class A : P { public int num2; public A(int r, int n) { num = r; num2 = n; } public double addSections() { return (double)num + (double)num2; } } public class B : P { public double g; public B(int r, double k) { num = r; g = k; } public double addSections() { return (double)num + g; } } public class MyClass { public MyClass() { List<A> listA; List<B> listB; //... helper(listA.Cast<P>()); //doesn't work helper(listB.Cast<P>().ToList()); //doesn't work either } public void helper(List<P> list) { //... } } ```