Question

when use new virtual key words to decorate the method? what is the affection? Like define an interface, and add a class to inherit the interface. but use the new virtual to realize the interface method.

 interface IPrinter
{
    void Print();
}

 public class PrinterOne : IPrinter
{
    public void Print() 
    {
        Console.WriteLine("PrinterOne.");
    }
}

public class PrinterTwo : PrinterOne
{
    public new virtual void Print()
    {
        Console.WriteLine("PrinterTwo.");
    }
}

public class PrinterThree : PrinterTwo
{
    public override void Print()
    {
        Console.WriteLine("PrinterThree.");
    }
}

public class PrinterFour : PrinterThree
{
    public override void Print()
    {
        Console.WriteLine("PrinterFour.");
    }
}

 static void Main(string[] args)
    {
        IPrinter iprinter = new PrinterFour();
        iprinter.Print();//the output is PrinterOne? why???
        Console.ReadLine();
    }

Answer 1

new and virtual are two (mostly-) unrelated keywords.

new means it shadows the base method.
virtual allows subclasses to override it.

Calling the method through the interface results in the base method being called, since the base method is not virtual and the derived classes don’t explicitly re-implement the interface (which would cause the method to be re-mapped)