C# link two properties together?

Question

I am trying to retrieve a List of Modules for a student and add them to a property in another class in order to display them. The aim I have is, when I create an instance of a person and their Programme has a certain name, it will retrieve the modules for that programme.

This is my method in my Programme class where I try to get the modules from the ListOfModules Method in the Modules class.

    public List<Modules> ModuleList
    {
        get
        {
            Modules m = new Modules();

            if (m.ListOfModules == null)
            {
                return null;
            }
            else
            {
                return m.ListOfModules;
            }
        }
    }

This is the ListOfModules method in the Modules Class.

internal List<Modules> ListOfModules
    {
        get 
        {
            if (_modules == null)
            {
                return _modules;
            }
            else
            {
                return _modules;
            }
        }
    }

and here is an example of how I add modules to a list of modules.

class CGP : Programmes
{
    List<Modules> modules;
    public CGP() :base("CGP") //CGP is the name of the programme
    {
        modules = new List<Modules>();
        modules.Add(new Modules("example 1"));
        modules.Add(new Modules("example 2"));
    }
}

So how can I go about getting the ModuleList method in the Programme class to get this list of modules from the ListOfModules method in the Modules class? I know that these modules are being added to the ListOfModules method but they I cant seem to work out how to link it with the ModuleList so I can print out that list.

I will appreciate any help or support as I have spent countless amount of hours trying to figure this out. Sorry for sounding like an amateur.

Answer 1

The root of your problem seems to be your ModuleList in your base class. I also don't understand why you have 2 levels of lists which seem to be the exact same implementation.

class Programme
{
    private List<Module> _modules = new List<Module>();

    public List<Module> Modules { get { return _moduleList; } }
}

class CGP : Programme
{
    public CGP() :base("CGP")
    {
        Modules.Add(new Module("example 1"));
        Modules.Add(new Module("example 2"));
    }
}

This especially seems silly:

internal List<Modules> ListOfModules
{
    get 
    {
        if (_modules == null)
        {
            return _modules;
        }
        else
        {
            return _modules;
        }
    }
}

You're returning the same thing either way so the check is unnecessary. It's essentially the same as just this:

internal List<Modules> ListOfModules { get { return _modules; } }

Answer 2

There is no direct way of linking these things in the manner you describe.

I would recommend using an interim service that Person can call into to retrieve modules by name.

Answer 3

Looks like your problem is that the List modules is declared in the CGP subclass, so the ModuleList property in the Programmes superclass cannot access it. If you want a property in the Programmes class to be able to return the modules that you are adding in the CGP constructor, then they need to be added to a property of the Programmes class, perhaps declared as protected, so that only subclasses can access it.

A few other things that seem odd: Why is your ModuleList getter creating a new Modules object and then returning a property of it? Does the constructor for Modules do something to create the data underlying that ListOfModules property or retrieve it from somewhere?

Why does your ListOfModules property check if _modules is null, then return it whether or not it is null? I'd skip that and the _modules property and do:

internal List<Modules> ListOfModules { get; private set; }