Question

Hey So I need to design a program that Can add Pickups or Delivery’s for a company to a list for my coursework, I have made a list called visits as shown bellow.

I would like to know how to add each pickup or delivery to the list in a way that it can differentiate between what is was originally so that I can show Only pickups or only delivery’s.

class List
{
/*
 * This object represents the List. It has a 1:M relationship with the Visit class
 */

    private List<Visits> visits = new List<Visits>();
    //List object use to implement the relationshio with Visits

    public void addVisits(Visits vis)
    {
        //Add a new Visit to the List
        visits.Add(vis);
    }

    public List<String> listVisits()
    {//Generate a list of String objects, each one of which represents a Visit in List.

        List<String> listVisits = new List<string>();
        //This list object will be populated with Strings representing the Visits in the lists

        foreach (Visits vis in visits)
        {
            String visAsString = vis.ToString();
            //Get a string representing the current visit object

            listVisits.Add(visAsString);
            //Add the visit object to the List
        }

        return listVisits;
        //Return the list of strings
    }

    public Visits getVisits(int index)
    {
        //Return the visit object at the <index> place in the list

        int count = 0;
        foreach (Visits vis in visits)
        {
            //Go through all the visit objects
            if (index == count)
                //If we're at the correct point in the list...
                return vis;
            //exit this method and return the current visit
            count++;
            //Keep counting
        }
        return null;
        //Return null if an index was entered that could not be found
    }

SHOW CODE

       /*
         * Update the list on this form the reflect the visits in the list
         */
        lstVisits.Items.Clear();
        //Clear all the existing visits from the list

        List<String> listOfVis = theList.listVisits();
        //Get a list of strings to display in the list box


        lstVisits.Items.AddRange(listOfVis.ToArray());
        //Add the strings to the listBox. Note to add a list of strings in one go we have to 
        //use AddRange and we have to use the ToArray() method of the list that we are adding

Answer 1

It looks like you have both Pickup and Delivery inheriting a common class called Visits^*.

Alter Visits to provide a way to differentiate the kinds of visits, for example, like this:

enum VisitKind {
    Pickup,
    Delivery
}

public class Visits {
    public VisitKind KindOfVisit {get;private set;}
    protected Visits(VisitKind kind) {
        KindOfVisit = kind;
    }
}

Now modify the constructors of Pickup and Delivery to pass the correct kind to the constructor of their superclass, like this:

public class Pickup : Visits {
    public Pickup() : base(VisitKind.Pickup) {}
}
public class Delivery : Visits {
    public Delivery() : base(VisitKind.Delivery) {}
}

Now you can examine the KindOfVisit property common to Pickup and Delivery in order to tell the kind of the visit at runtime:

public IList<Delivery> GetDeliveries() {
    var res = new List<Delivery>();
    foreach (var v in visits) {
        if (v.KindOfVisit == VisitKind.Delivery) {
            res.Add((Delivery)v);
        }
    }
    return res;
}

This solution is not ideal, because when someone adds a new kind of visit, the code that processes visits would continue compiling as usual. A solution to this problem is a lot harder than adding a property, though: one solution is to employ the Visitor Pattern which is better than a simple Kind attribute, but it has limitations of its own.

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^* Naming a class with a plural of a noun is unconventional – Visit would probably be a better name.