Can I create a class that is inherited from a class and from interfaces in Delphi?

Question

I have a class TDevice. Some devices will have a cellular module. So I create an Interface IIMEI. Others devices will have an Ethernet Module. So I create an Interface IMacAddress.

So, I'd like to create another class that is a child of TDevice and implements IIMEI or IMacAddress or both.

Is it possible in Delphi?

Answer 1

The easiest option is to derive TDevice from TInterfaced Object and just extend your descendants with the additional methods. Beware of interface reference counting, though, otherwise you will end up with lots of unexpected access violations.

Alternatively you can write a wrapper object that descends from TInterfacedObject and delegates the implementation of the interfaces to TDevice descendants. In that case reference counting will be less of a problem.

TMacAddressWrapper = class(TInterfacedObject, IMacAddress)
private
  FDevice: TDevice;
  property Device: TDevice read FDevice implements IMacAddress;
public
  constructor Create(_Device: TDevice);
end;

constructor TMacAddressWrapper.Create(_Device: TDevice);
begin
  inherited Create;
  FDevice := _Device;
end;