best practice for Undo Redo implementation
I need to implement Undo/Redo frame work for my window application(editor like powerpoint), what should be the best practice to follow, how would be handle all property changes of my objects and it reflection on UI.
Answer
There are two classic patterns to use. The first is the memento pattern which is used to store snapshots of your complete object state. This is perhaps more system intensive than the command pattern, but it allows rollback very simply to an older snapshot. You could store the snapshots on disk a la PaintShop/PhotoShop or keep them in memory for smaller objects that don't require persistence. What you're doing is exactly what this pattern was designed for, so it should fit the bill slightly better than the Command Pattern suggested by others.
Also, an additional note is that because it doesn't require you to have reciprocal commands to undo something that was previously done, it means that any potentially one way functions [such as hashing or encryption] which can't be undone trivially using reciprocal commands can still be undone very simply by just rolling back to an older snapshot.
Also as pointed out, the command pattern which is potentially less resource intensive, so I will concede that in specific cases where:
- There is a large object state to be persisted and/or
- There are no destructive methods and
- Where reciprocal commands can be used very trivially to reverse any action taken
the command pattern may be a better fit [but not necessarily, it will depend very much on the situation]. In other cases, I would use the memento pattern.
I would probably refrain from using a mashup of the two because I tend to care about the developer that's going to come in behind me and maintain my code as well as it being my ethical responsibility to my employer to make that process as simple and inexpensive as possible. I see a mashup of the two patterns easily becoming an unmaintainable rat hole of discomfort that would be expensive to maintain.