“Interface not implemented” when Returning Derived Type

Question

The following code:

public interface ISomeData
{
    IEnumerable Data { get; }
}

public class MyData : ISomeData
{
    private List

        

Answer 1

For what you want to do you'll probably want to implement the interface explicitly with a class (not interface) member that returns the List instead of IEnumerable...

public class MyData : ISomeData
{
    private List m_MyData = new List();
    public List Data
    {
        get
        {
            return m_MyData;
        }
    }

    #region ISomeData Members

    IEnumerable ISomeData.Data
    {
        get
        {
            return Data.AsEnumerable();
        }
    }

    #endregion
}

Edit: For clarification, this lets the MyData class return a List when it is being treated as an instance of MyData; while still allowing it to return an instance of IEnumerable when being treated as an instance of ISomeData.