I have a class that has private fields... (cars)
I then inherit from this class... (Audi)
In the (Audi) class, when I type this. in the constructor...
the private fields are not available...
Do I need to do anything special to expose this private fields in (cars) class so that they are accessible via this. in (Audi class)?
One (bad) option is to make the fields protected - but don't do this; it still breaks proper encapsulation. Two good options:
examples:
public string Name { get; protected set; }
(C# 2.0)
private string name;
public string Name {
get { return name; }
protected set { name = value; }
}
or:
class BaseType {
private string name;
public BaseType(string name) {
this.name = name;
}
}
class DerivedType : BaseType {
public DerivedType() : base("Foo") {}
}
Philippe's suggestion to declare the fields as protected instead of private will indeed work - but I suggest you don't do it anyway.
Why should a derived class care about an implementation detail of how the data is stored? I suggest you expose protected properties which are (currently) backed by those fields, instead of exposing the fields themselves.
I treat the API you expose to derived classes as very similar to the API you expose to other types - it should be a higher level of abstraction than implementation details which you may want to change later.
You should declare them as "protected" instead of private
protected is a bad idea.
You are probably looking for a concept called constructor inheritance. You can forward arguments to the base classes constructor - see this example, where the Audi has a flag indicating whether it's an S-Line edition or not:
namespace ConstructorInheritance
{
abstract class Car
{
private int horsePower;
private int maximumSpeed;
public Car(int horsePower, int maximumSpeed)
{
this.horsePower = horsePower;
this.maximumSpeed = maximumSpeed;
}
}
class Audi : Car
{
private bool isSLineEdition = false;
// note, how the base constructor is called _and_ the S-Line variable is set in Audi's constructor!
public Audi(bool isSLineEdition, int horsePower, int maximumSpeed)
: base(horsePower, maximumSpeed)
{
this.isSLineEdition = isSLineEdition;
}
}
class Program
{
static void Main(string[] args)
{
Car car = new Audi(true, 210, 255);
// break here and watch the car instance in the debugger...
}
} }
