Question

Consider this example:

public interface IAccount
{
    string GetAccountName(string id);
}

public class BasicAccount : IAccount
{
    public string GetAccountName(string id)
    {
        throw new NotImplementedException();
    }

}

public class PremiumAccount : IAccount
{
    public string GetAccountName(string id)
    {
        throw new NotImplementedException();
    }

    public string GetAccountName(string id, string name)
    {
        throw new NotImplementedException();
    }
}

protected void Page_Load(object sender, EventArgs e)
{

    IAccount a = new PremiumAccount();

    a.GetAccountName("X1234", "John"); //Error
}

How can I call the overridden method from the client without having to define a new method signature on the abstract/interface (since it is only an special case for the premium account)? I’m using abstract factory pattern in this design… thanks…

Answer 1

Well, considering it’s only defined for the PremiumAccount type, the only way you know you can call it is if a is actually a PremiumAccount, right? So cast to a PremiumAccount first:

IAccount a = new PremiumAccount();

PremiumAccount pa = a as PremiumAccount;
if (pa != null)
{
    pa.GetAccountName("X1234", "John");
}
else
{
    // You decide what to do here.
}