CODEWITHSUNDEEP
c#listabstract-classinstantiation
Kiran Ramaswamy
Kiran Ramaswamy

Reputation: 806

Collection of objects with common Abstract base class

I have an abstract class called generic, implemented as follows:

public abstract class generic
{
    public string creatorID { get; set; }
    public string itemID { get; set; }
    public string name { get; set; }
    public DateTime creationDate { get; set; }
    public string pageName { get; set; }
    ...
}

This is implemented through several classes, such as:

public class file : generic
{
    public file(string _itemID, string host, string languageReferenceID)
    {
        DataTable dt = GetRecordsFromDatabase(string _itemID, string host, string languageReferenceID);
        if (dt.Rows.Count > 0)
            setParameters(dt.Rows[0]);
        ...
    }

    private void setParameters(DataRow dr)
    {
        creatorID = dr["f_MemberID"].ToString();
        itemID = dr["f_ID"].ToString();
        name = dr["f_Name"].ToString();
        creationDate = DateTime.Parse(dr["f_DateCreated"].ToString());
        pageName = "files";
        ...
    }
}

What I'm trying to do is create a List of objects of different instantiations of that abstract generic class. Here's what I'm attempting to do:

    public List<generic> getAlerts(string host, string languageReferenceID)
    {            
        DataTable dt = GetAlertsFromDatabase(host, languageReferenceID);

        List<generic> alertList = new List<generic>();

        foreach (DataRow dr in dt.Rows)
        {
            generic g = new generic();

            g.itemID = dr["itemID"];
            g.description = dr["description"];
            g.pageName = dr["pageName"];

            g.Add(m);
        }

        return alertList;
    }

Now, of course, this is throwing an error on the line with:

generic g = new generic();

Since generic is an abstract class, it can't be instantiated as an object.

My question is - how do I accomplish my objective, given the requirements I've listed? Should I create a new class implementing the abstract class generic, for the sole purpose of instantiating lists of type generic? That seems like an odd solution to me, but it's the only thing I can think of right now.

Upvotes: 0

Views: 268

Answers (1)

15ee8f99-57ff-4f92-890c-b56153
15ee8f99-57ff-4f92-890c-b56153

Reputation: 37059

To me, this looks like a class factory.

You need a method that takes a DataRow, looks at its fields, and decides which subclass of generic should be created for that row. Then it creates the appropriate object newObj, calls newObj.setParameters(dr), and returns newObj.

Preferably, the actual factory method doesn't take a DataRow, but rather just the one scalar value (int, string, whatever) that indicates the type to be created.

Perhaps the class factory is passed in by dependency injection; you could go simple or elaborate on this.

Upvotes: 2

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