OfType参数 <????> 在C＃方法中使用时

Question

I have this code to get "A" as a filtered result.

public static void RunSnippet()
{
    Base xbase = new Base(); 
    A a = new A(); 
    B b = new B();
    IEnumerable<Base> list = new List<Base>() { xbase, a, b };
    Base f = list.OfType<A>().FirstOrDefault();
    Console.WriteLine(f);
}

I need to use IEnumerable<Base> list = new List<Base>() {xbase, a, b}; from a function as follows:

public static Base Method(IEnumerable<Base> list, Base b (????)) // I'm not sure I need Base b parameter for this?
{
    Base f = list.OfType<????>().FirstOrDefault();
    return f;
}

public static void RunSnippet()
{
    Base xbase = new Base(); 
    A a = new A(); 
    B b = new B();
    IEnumerable<Base> list = new List<Base>() { xbase, a, b };
    //Base f = list.OfType<A>().FirstOrDefault();
    Base f = Method(list);
    Console.WriteLine(f);
}

What parameter do I use in '????' to get the same result from the original code?

Answer 1

It seems like you are looking for a generic way to do what is in Method based on different children types of Base . You can do that with:

public static Base Method<T>(IEnumerable<Base> b) where T: Base
{
    Base f = list.OfType<T>().FirstOrDefault();
    return f;
}

This will return the first instance from b that is of type T (which has to be a child of Base ).

Answer 2

If you want to query on a type, you can try something like this:

public static Base Method(IEnumerable<Base> list, Type typeToFind)
{
   Base f =  (from l in list  
       where l.GetType()== typeToFind 
               select l).FirstOrDefault();
   return f;
}

If it's not what you are searching for, please clarify.