For a personal project, I'm working on a small web-based game.
I have a Card
class that has a Status
property, and there are case statements all over the place. I thought, hey, this is a great oppurtunity for Replace Conditional with Polymorphism!
The problem is, I have a couple methods that do stuff like this:
public class Card
{
public void ChangeStatus()
{
switch (Status)
{
case MyStatusEnum.Normal:
Status = MyStatusEnum.Underwater;
break;
case MyStatusEnum.Underwater:
Status = MyStatusEnum.Dead;
break;
// etc...
}
}
}
When refactoring it in the new NormalCard
class, I'm overriding the ChangeStatus
method like this:
public override void ChangeStatus()
{
base.Status = MyStatusEnum.Underwater;
}
The problem is this object of NormalCard
has a status of Underwater
. I can't reassign the type of this
, and I don't really want to change the return of the methods from void
to CardBase
. What options do I have? Is there a standard way of doing this?
Edit Tormod set me straight. I want the State Pattern. Thanks all!
Best Answer
In your case, I'd have a
Card
object that contains aCardStatus
property. The subtypes ofCardStatus
correspond to the previous enum values. Refactor behaviour that depends on the current status except the state transition to be inside the CardStatus subtypes.The state transition that's in your first example should, IMO, remain inside the
Card
object. The state changing feels more like a behaviour of the containing card than of the state object. What you can do is have the CardStatus objects tell you what state to transition to after an event.A rough example: (obviously there's many more variations on this that could be used.)
API
Status implementations