强制转换对象为接口

可用is运算符检查是否支持接口，用as运算符转换接口，如：

/*
  Example8_4.cs illustrates casting an object
  to an interface
 */

using System;


// define the IDrivable interface
public interface IDrivable
{

  // method declarations
  void Start();
  void Stop();

  // property declaration
  bool Started
  {
    get;
  }

}


// Car class implements the IDrivable interface
public class Car : IDrivable
{

  // declare the underlying field used by the Started property
  private bool started = false;

  // implement the Start() method
  public void Start()
  {
    Console.WriteLine("car started");
    started = true;
  }

  // implement the Stop() method
  public void Stop()
  {
    Console.WriteLine("car stopped");
    started = false;
  }

  // implement the Started property
  public bool Started
  {
    get
    {
      return started;
    }
  }
  
}


class Example8_4
{

  public static void Main()
  {

    // create a Car object
    Car myCar = new Car();

    // use the is operator to check that myCar supports the
    // IDrivable interface
    if (myCar is IDrivable)
    {
      Console.WriteLine("myCar supports IDrivable");
    }

    // cast the Car object to IDrivable
    IDrivable myDrivable = (IDrivable) myCar;

    // call myDrivable.Start()
    Console.WriteLine("Calling myDrivable.Start()");
    myDrivable.Start();
    Console.WriteLine("myDrivable.Started = " +
      myDrivable.Started);

    // call myDrivable.Stop()
    Console.WriteLine("Calling myDrivable.Stop()");
    myDrivable.Stop();
    Console.WriteLine("myDrivable.Started = " +
      myDrivable.Started);

    // cast the Car object to IDrivable using the as operator
    IDrivable myDrivable2 = myCar as IDrivable;
    if (myDrivable2 != null)
    {
      Console.WriteLine("Calling myDrivable2.Start()");
      myDrivable2.Start();
      Console.WriteLine("Calling myDrivable2.Stop()");
      myDrivable2.Stop();
      Console.WriteLine("myDrivable2.Started = " +
        myDrivable2.Started);
    }

  }

}