How to access to the parent object in c#

问题:

I have a "meter" class. One property of "meter" is another class called "production". I need to access to a property of meter class (power rating) from production class by reference. The powerRating is not known at the instantiation of Meter.

How can I do that ?

Thanks in advance

public class Meter
{
   private int _powerRating = 0; 
   private Production _production;

   public Meter()
   {
      _production = new Production();
   }
}

回答1:

Store a reference to the meter instance as a member in Production:

public class Production {
  //The other members, properties etc...
  private Meter m;

  Production(Meter m) {
    this.m = m;
  }
}

And then in the Meter-class:

public class Meter
{
   private int _powerRating = 0; 
   private Production _production;

   public Meter()
   {
      _production = new Production(this);
   }
}

Also note that you need to implement an accessor method/property so that the Production class can actually access the powerRating member of the Meter class.

回答2:

I wouldn't reference the parent directly in the child objects. In my opinion the childs shouldn't know anything about the parents. This will limits the flexibility!

I would solve this with events/handlers.

public class Meter
{
    private int _powerRating = 0;
    private Production _production;

    public Meter()
    {
        _production = new Production();
        _production.OnRequestPowerRating += new Func<int>(delegate { return _powerRating; });
        _production.DoSomething();
    }
}

public class Production
{
    protected int RequestPowerRating()
    {
        if (OnRequestPowerRating == null)
            throw new Exception("OnRequestPowerRating handler is not assigned");

        return OnRequestPowerRating();
    }

    public void DoSomething()
    {
        int powerRating = RequestPowerRating();
        Debug.WriteLine("The parents powerrating is :" + powerRating);

    }

    public Func<int> OnRequestPowerRating;
}

In this case I solved it with the Func<> generic, but can be done with 'normal' functions. This why the child(Production) is totally independent from it's parent(Meter).

---

But! If there are too many events/handlers or you just want to pass a parent object, i would solve it with an interface:

public interface IMeter
{
    int PowerRating { get; }
}

public class Meter : IMeter
{
    private int _powerRating = 0;
    private Production _production;

    public Meter()
    {
        _production = new Production(this);
        _production.DoSomething();
    }

    public int PowerRating { get { return _powerRating; } }
}

public class Production
{
    private IMeter _meter;

    public Production(IMeter meter)
    {
        _meter = meter;
    }

    public void DoSomething()
    {
        Debug.WriteLine("The parents powerrating is :" + _meter.PowerRating);
    }
}

This looks pretty much the same as the solution mentions, but the interface could be defined in another assembly and can be implemented by more than 1 class.

---

Regards, Jeroen van Langen.

回答3:

You would need to add a property to your Production class and set it to point back at its parent, this doesn't exist by default.

回答4:

Why not change the constructor on Production to let you pass in a reference at construction time:

public class Meter
{
   private int _powerRating = 0; 
   private Production _production;

   public Meter()
   {
      _production = new Production(this);
   }
}

In the Production constructor you can assign this to a private field or a property. Then Production will always have access to is parent.

回答5:

You could maybe add a method to your Production object called 'SetPowerRating(int)' which sets a property in Production, and call this in your Meter object before using the property in the Production object?

回答6:

something like this:

  public int PowerRating
    {
       get { return base.PowerRating; } // if power inherits from meter...
    }