Is it possible for a non-generic class contain a generic list in .NET (C# or VB.NET)?

Question

I'm hoping someone can assist me with understanding if/how something like this is possible.

In this scenario, imagine you are trying to model a grid like a spreadsheet or in a DB, but where the data in each column can only be of one data type.

Example: Column 1 can only contain integers.

I created a generic class to model the column structure that looks like this:

public class CollectionColumn<T>
{
private string _name;
private string _displayName;

private List<T> _dataItems = new List<T>();

public string Name {
    get { return _name; }
    set { _name = value; }
}

public string DisplayName {
    get { return _displayName; }
    set { _displayName = value; }
}


public List<T> Items {
    get { return _dataItems; }
    set { _dataItems = value; }
}
}

Now what I want to do is have a container for the various columns (there could be CollectionColumn, CollectionColumn, etc.) with it's own properties, but I'm not sure how to do that where I can still access the columns and the data within them when I don't know their types.

This is a .NET 2.0 project so something like dynamic would not work, maybe a list of object? I am also not sure if there is a way to do this with interfaces.

public class ColumnCollection
{
public int Id { get; set; }
public string ContainerName { get; set; }

private List<CollectionColumn<T>> _columns;
public List<CollectionColumn<T>> Columns {
    get { return _columns; }
    set { _columns = value; }
}

}

What I want to be able to do is add various CollectionColumn's to the Columns collection of a ColumnCollection so I can have columns containing various types of data.

Any help would be very much appreciated.

Answer 1

This is a fairly common problem. What you need to do is either declare a non-generic base class that your generic class inherits from or a non-generic interface that your generic class implements. You can then make your collection of that type.

For example,

public abstract class CollectionColumnBase
{
    private string _name;
    private string _displayName;

    public string Name {
        get { return _name; }
        set { _name = value; }
    }

    public string DisplayName {
        get { return _displayName; }
        set { _displayName = value; }
    }

    public abstract object GetItemAt(int index);
}

public class CollectionColumn<T> : CollectionColumnBase
{
    private List<T> data = new List<T>();

    public overrides object GetItemAt(int index)
    {
        return data[index];
    }

    public List<T> Items
    {
        get { return data; }
        set { data = value; }
    }
}

public class ColumnCollection
{
    public int Id { get; set; }
    public string ContainerName { get; set; }

    private List<CollectionColumnBase> _columns;
    public List<CollectionColumnBase> Columns {
        get { return _columns; }
        set { _columns = value; }
    }
}