Override abstract method, but keep method abstract?

Override abstract method, but keep method abstract?

I want to override an abstract method, but keep it abstract so derived
classes are required to implement it themselves.
public abstract class ComponentController
{
public abstract void CreateCustomColumns();
}
public abstract class ClientComponentController : ComponentController
{
public override void CreateCustomColumns()
{
// All grids to do with columns should show these columns.
Grid.AddColumn("Client" ...
Grid.AddColumn("ClientLocation" ...
Grid.AddColumn("ClientPhoto" ...
}
}
public class ClientInvoicesComponentController : ClientComponentController
{
public override void CreateCustomColumns()
{
base.CreateCustomColumns();
// On top of the generic columns, I also want to show these.
Grid.AddColumn("InvoiceNumber" ...
Grid.AddColumn("InvoiceDate" ...
}
}
public class ClientCommunicationsComponentController :
ClientComponentController
{
public override void CreateCustomColumns()
{
base.CreateCustomColumns();
// On top of the generic columns, I also want to show these.
Grid.AddColumn("CommunicationDate" ...
Grid.AddColumn("CommunicationType" ...
}
}
In this code, ClientInvoicesComponentController is not required to
implement CreateCustomColumns() because this is not allowed:
public abstract class ClientComponentController : ComponentController
{
public abstract override void CreateCustomColumns()
{
Grid.AddColumn("Client" ...
Grid.AddColumn("ClientLocation" ...
Grid.AddColumn("ClientPhoto" ...
}
}
--> "Abstract method cannot declare a body"
So, how can I override CreateCustomColumns() in ClientComponentController,
but still force it to be overridden again in derived classes like
ClientInvoicesComponentController?
Of course it still CAN be overridden anyway, but there is nothing to
indicate to the developer that it MUST be overridden... which is my aim.
-Brendan