投射到列表中的特定类型

Question

So let's say we have a class named Car and three other classes (Opel , Volkswagen and Peugeot ) which inherits information from Car but in addition each class has a specific variable.

So I create a new List of Cars in which I add those three types CarOpel..etc.

Opel CarOpel = new Opel(parameters);

etc...

List<Car> Cars = new List<Car>();
Car.Add(CarOpel);

etc...

How can I access those specific variables from each class when I use the "foreach" statement

foreach ( Car car in Cars )
{
      // how to convert *car* in *Opel* , *Volkswagen* or *Peugeot* to get that specific variable?
}

?

Answer 1

var opelCars = cars.OfType<Opel>()


foreach ( Opel car in cars.OfType<Opel>())
{
}

Other solution is to use is keyword

foreach ( Car car in cars)
{
    if(car is Opel) 
    {
        var opel = (Opel)car;
    }
}

If you need to downcast your cars in order to do something it may suggest that your inheritance hierarchy is wrong or your method is not in the proper place. It probably should be a virtual method in Car class which is overridden in derived classes. Also consider reading about visitor pattern.

Answer 2

You have to cast it down to the specific type.

foreach(Car car in Cars) 
{ 
    CarOpel opel = car as CarOpel;

    if (opel != null)
    {
        //do something with Opel
    }
}

Answer 3

Use is or as operator.

foreach ( Car car in Cars )
{

  if (car is Opel)
  {
   // do opel operation
    var op = (Opel)car;
  }

  if (car is Volkswagen)
  {
   // do VW operation
    var vw = (Volkswagen)car;
  }
}