Question

Consider following code

    public class City
    {
        public string Name { get { return "New York"; } }

        Building empEstate;
        Building nyTimes;
        public void Init()
        {
            // I hate passing "this" to all object
            empEstate = new EmpEstate(this); 
            setSomeProperty(empEstate);
            // any one can create new object of some other city 
            // and pass to the building
            nyTimes = new NYTimes(this);
            ...
            other = new OtherBuildings(this)
        }

        public void PrintAddresses()
        {
            empEstate.Print();
            nyTimes.Print();
            ...
            other.Print();
        }
    }

    public abstract class Building {
        City _city;
        public Building(City city){
            this._city = city;
        }
        public abstract string Name { get;}
        public void Print(){
            Console.WriteLine(this.Name);
            Console.Write(",");
            Console.WriteLine(this._city.Name);
        }
    }

1. First thing I want better solution to this approach. Print is just an example. Actually each building object raise some event to City object. I don’t want to add handler to each building as there could be several buildings in city. Also I do not want to add each of them into list, as it is two task for each building (one initialization and second add to list, one forget to add to list when writing new building). For this, I want caller to be automatically available to callee, like Parent property of control (though it was added to this.Controls)

2. Using memory, can we know who is the parent of current object. How does GC knows that object is not being referenced (including creator). Can’t we create a method (safe or unsafe) using memory to identify the caller object. I see we can use StackTrace to see the call hirarchy, can we intercept here when a new object is being created.

Answer 1

Building factory on city solved my problem of passing this to each object

public interface ICity
    {
        string Name { get; }
    }
    public abstract class City : ICity
    {
        public T CreateBuilding<T>()
        {
            T buildingInstance = Activator.CreateInstance<T>();
            ((IBuilding)buildingInstance).SetCity(this);
            return buildingInstance;
        }

        public abstract string Name { get; }
    }

    interface IBuilding
    {
        ICity City { get; }
        void SetCity(ICity city);
    }
    public abstract class Building : IBuilding
    {
        private ICity _city;
        public ICity City { get { return _city; } }
        public void IBuilding.SetCity(ICity city)
        {
            this._city = city;
        }
        public abstract string Name { get; }
        public void Print()
        {
            Console.WriteLine(this.Name);
            Console.Write(",");
            Console.WriteLine(this._city.Name);
        }
    }
    public class EmpEstate : Building
    {
        public override string Name { get { return "Emp State"; } }
    }
    public class NYTimes : Building
    {
        public override string Name { get { return "NY Times"; } }
    }
    public class NewYorkCity : City
    {
        public override string Name { get { return "New York"; } }

        EmpEstate empEstate;
        NYTimes nyTimes;
        public void Init()
        {
            // Now I dont need to pass this
            empEstate = this.CreateBuilding<EmpEstate>();
             setSomeProperty(empEstate);
            // now any one cannot create building in new your and 
            // say it belongs to Philedelphia :)
            nyTimes = this.CreateBuilding<NYTimes>();
        }

        public void PrintAddresses()
        {
            empEstate.Print();
            nyTimes.Print();
        }
    }

Problem was there were several classes already created and for new functionality we needed the creator object in the base class of Building Object. We did not wanted to modify the constructor of each class and pass this object to each. And City class (in example) was basically code on plugin side, so allowing them to pass city (if plugin developer pass wrong city) may disturb the functionality of entire app. So modifying the plugin base solved my purpose. Suggestions are welcome.