我们可以在c＃的方法中同时使用virtual和new关键字吗？

Question

我们可以在c＃的方法中同时使用virtual和new关键字吗？

Answer 1

Yes. You would be defining a method that hid a method of a parent and allowed children to override. The behavior might be a little strange though. Say you had the following classes:

public class A
{
    public void DoSomething(){ Console.WriteLine("42!"); }
}

public class B : A
{
    public virtual new void DoSomething(){ Console.WriteLine("Not 42!"); }
}

public class C : B
{
    public override void DoSomething(){ Console.WriteLine("43!"); }
}

Then your execution would look something like:

A a = new A();
A bAsA = new B();
A cAsA = new C();
B b = new B();
B cAsB = new C();
C c = new C();

a.DoSomething(); // 42!

b.DoSomething(); // Not 42!
bAsA.DoSomething(); // 42!

c.DoSomething(); // 43!
cAsB.DoSomething(); // 43!
cAsA.DoSomething(); // 42!

Answer 2

Yes you can combine both.

virtual allows a method to be overridden in a derived class

new allows you to hide the old method.

Both are complementary and not contradicting.

Answer 3

Don't hesitate to just try this yourself, Visual Studio makes it easy.

class Base {
    public virtual void Method() { }
}
class Derived : Base {
    public virtual new void Method() { }
}