I now have A1, A2, A3, A4 four class inherits A, then I pick parameter will receive the A1 ~ A4 in any class, so I use A class received (parameter is the way with A request to receive at this time), then I want to do data processing, may need to use the inside of the A1 attribute, if I directly use point A, is A point not to come out, can only transform types, strong would turn again to modelling is unusual, now what can I do?