C# Object Inheritance

Question

I am trying to create a base class in c# that I can extend out to sub classes.

For example:

public class ObjectsInTheSky 
{
    public string Size, Shape;
    public float Mass;
    public int DistanceFromEarth;
    public bool hasAtmosphere, hasLife;
    public enum ObjectTypes {Planets,Stars,Moons}

    public ObjectsInTheSky( int id ) 
    {
        this.Load( id );
    }
    public void Load( int id) 
    {
        DataTable table = Get.DataTable.From.DataBase(id);

        System.Reflection.PropertyInfo[] propInfo = this.GetType().GetProperties();
        Type tp = this.GetType();
        foreach (System.Reflection.PropertyInfo info in propInfo)
        {
            PropertyInfo p = tp.GetProperty(info.Name);
            try
            {
                if (info.PropertyType.Name == "String")
                {
                    p.SetValue(this, table.Rows[0][info.Name].ToString(), null);
                }
                else if (info.PropertyType.Name == "DateTime")
                {
                    p.SetValue(this, (DateTime)table.Rows[0][info.Name], null);
                }
                else
                {
                    p.SetValue(this, Convert.ToInt32(table.Rows[0][info.Name]), null);
                }
            }
            catch (Exception e) 
            {
                Console.Write(e.ToString());
            }
        }
    }
}

public class Planets : ObjectsInTheSky 
{
    public Moons[] moons;
}

public class Moons : ObjectsInTheSky 
{

}

public class Stars : ObjectsInTheSky 
{
    public StarTypes type;
    public enum StarTypes {Binary,Pulsar,RedGiant}
}

My problem is when I try to use an object:

Stars star = new Stars(142);

star.type does not exists and property of star, it exists as star.star.type but completely inaccessable, or I can not figure out how to access it.

I do not know if I'm extending the ObjectsInTheSky property properly or not. Any help or pointers will be greatly appreciated.

Your Stars class only has a parameterless constructor, provided by default by the compiler. — Jon Skeet
– Jon Skeet, Commented Jan 21, 2013 at 17:24
Just a point for the future, @user1224302, that the code for Load wasn't required (i.e. just put something like /* stuff loaded here */ inside the body of the method) - people don't always bother to scroll down code examples (even though we really should). That said, though, it's a damn site better to actually have code than none at all - so you've already done 100% better than 50% of new users ;) — Andras Zoltan
– Andras Zoltan, Commented Jan 21, 2013 at 17:59

Davin Tryon · Accepted Answer · 2013-01-21 19:34:24Z

6

It looks as though you are trying to use a constructor that is not defined on your subclass Stars or the base class.

Stars star = new Stars(142);

If you are trying to use the .Load(int) method then you would need to do this:

Stars star = new Stars();
star.Load(142);

Or, if you are trying to use the base constructor, you need to define it in the subclass:

public class Stars : ObjectsInTheSky 
{
    public Stars(int id) : base(id) // base class's constructor passing in the id value
    {
    }

    public Stars()  // in order to not break the code above
    {
    }

    public StarTypes type;
    public enum StarTypes {Binary,Pulsar,RedGiant}
}

edited Jan 21, 2013 at 19:34

answered Jan 21, 2013 at 17:25

Davin Tryon

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5 Comments

Servy Over a year ago

He probably just wants to add the additional constructor to all child types, since Load probably shouldn't be public.

Andras Zoltan Over a year ago

...Or add an int constructor in Stars that channels to the same in ObjectsInTheSky

Davin Tryon Over a year ago

Thanks, I added the creation of the sub type's constructor as well.

Andras Zoltan Over a year ago

cool +1 then - although worth pointing out then that if that updated code is followed, then your second code block can't be used unless a default constructor is also added :)

Davin Tryon Over a year ago

@AndrasZoltan Again, thanks, added another constructor and comment.

Servy · Accepted Answer · 2013-01-21 17:27:12Z

2

Constructors in C# are not inherited. You need to add the additional constructor overloads to each of the base classes:

public class Stars : ObjectsInTheSky 
{
    public Stars(int id) : base(id) { }

    public StarTypes type;
    public enum StarTypes {Binary,Pulsar,RedGiant}
}

This will create a constructor that just calls the base class's constructor for you.

answered Jan 21, 2013 at 17:27

Servy

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