Filtering the object of a type with OfType in C#

问题

I have a base class Base, and class A/B that inherits from it.

public class Base
{
    int x;
}
public class A : Base
{
    int y;
}
public class B : Base
{
    int z;
}

I tried to use OfType to filter the only object that I need as follows:

public static void RunSnippet()
{
    Base xbase; A a; B b;
    IEnumerable<Base> list = new List<Base>() {xbase, a, b};
    Base f = list.OfType<A>; // I need to get only the object A
    Console.WriteLine(f);
}

When I compiled the code, I got this error:

error CS0428: Cannot convert method group 'OfType' to non-delegate type 'Base'. Did you intend to invoke the method?

What's wrong with the code?

回答1:

There are two problems:

• OfType returns IEnumerable<T>, not T
• It's a method - you forgot the brackets

Perhaps you wanted:

Base f = list.OfType<A>().FirstOrDefault();

?

回答2:

Brackets ?

This is a function and not operator.

Base f = list.OfType<A>()

Check out the reference:

Enumerable.OfType(Of TResult) Method

来源：https://stackoverflow.com/questions/10165660/filtering-the-object-of-a-type-with-oftype-in-c-sharp