Csharp Inheritance And Fields -- Per Erik Strandberg

In this example I try to be stupid in my implementation of a family of classes and then work around my stupid planning with a number of interesting functions to examine classes.

Also see this thread from microsoft.public.dotnet.languages.csharp: [1]

The Code

The code is available here: [2]

This is pretty much the inheritance diagram. In musiCar we introduce the member hasStereo. In homeMadeCar we add an identical member.

  // car ----- musicar ---- nicecar
  //  \            \
  //   \            +------ oldcar 
  //    \
  //     +---- homemadecar

We then create a method to display all info about a car.

  public static void displayCar(Car myCar)

Here we might want to print if the car has a stereo:

if (myCar is musiCar)
{
  if (((musiCar)myCar).hasStereo)
    Console.WriteLine("   - has a stereo");
  else
    Console.WriteLine("   - has no stereo");

  // ...
}

Now: what if it is some other class that also might have a stereo. We want to print that aswell. This is the interesting part, we use GetField on the type of car we are dealing with.

if (!(myCar is musiCar))
{
  try
  {
    Type T = myCar.GetType();
    FieldInfo field = T.GetField("hasStereo");

    if ((bool)field.GetValue(myCar))
      Console.WriteLine("   - has a stereo :)");
    else
      Console.WriteLine("   - has no stereo :)");
  }
  catch (Exception ex)
  {
    Console.WriteLine("  the 'hasStereo' of this car was not a bool...");
    Console.WriteLine("  {0}", ex.Message);
  }
}

Of course we want to wrap this around a try catch since we really do not know what the car looks like.

I made the main function like this

static void Main(string[] args)
{

  oldCar c1 = new oldCar();
  c1.age = 25;
  c1.color = "beige";
  c1.hasStereo = false;
  c1.miles = int.MaxValue / 2;
  c1.nickname = "ugly betty";

  niceCar c2 = new niceCar();
  c2.color = "light blue metallic";
  c2.hasMP314Player = true;
  c2.hasStereo = c2.hasMP314Player;
  c2.miles = 1337;
  c2.nickname = "Turing the Tempest";

  homeMadeCar c3 = new homeMadeCar();
  c3.color = "black";
  c3.hasStereo = true;
  c3.isEpa = true;
  c3.miles = 555;
  c3.nickname = "KB::P_WAGON";

  Console.WriteLine();
  Console.WriteLine("CAR 1");
  displayCar(c1);

  Console.WriteLine();
  Console.WriteLine("CAR 2");
  displayCar(c2);

  Console.WriteLine();
  Console.WriteLine("\"CAR\" 3");
  displayCar(c3);

}

The output

>epatraktor

CAR 1
The beige car...
   - is called 'ugly betty'
   - has run for '1073741823' miles
   - has no stereo
   - is 25 years old

CAR 2
The light blue metallic car...
   - is called 'Turing the Tempest'
   - has run for '1337' miles
   - has a stereo
   - has an MP314 player

"CAR" 3
The black car...
   - is called 'KB::P_WAGON'
   - has run for '555' miles
   - this is in fact an epatraktor.
   - has a stereo :)

Csharp Inheritance And Fields

The Code

The output

See Also