I'm working on some electronics simulation software that manages projects that are organised in a tree structure: modules in modules in modules, etc... (For instance, the project may contain modules A and B, module A may contain module C and C may contain D and E, and so on.)

I would like to add an undo/redo feature to the program but I don't know if the undo/redo stacks should be on a per-module (per-node) basis (such that the changes can be undone independently) or on a project basis (such that holding Ctrl+Z will revert to initial save state if held long enough).

Will users find it confusing if it is on a per-module basis? Would they prefer it on the contrary? But can it cause chronology problems? Is there a consensus on such a problem? Which is better and why?

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You should bind your undo-stack to a component and any change to the components model should lead to a command on the undo-stack. So if the user has access to multiple trees each tree should have unique undo-stack. If your model is displayed within on tree component you'll have one undo-stack.

I believe the user will be very much confused if you choose the per-module-undo within one tree component. It also does not answer well to this question: Why would you make an exception regarding the create-module, delete-module commands?

What adds up to the users confusion is that you'll also have something much more complex to implement.

  • "Why would you make an exception regarding the create-module, delete-module commands?" The entire project can be seen as a module: the "root module". Those changes could be added to the undo stack of the root. And if create-module or delete-module commands are executed within a module, then they could be added to the undo stack of the module currently being edited. Doesn't seem like there's an exception to me. Aug 4 at 20:01
  • "you'll also have something much more complex to implement" Actually, if the undo stack is on a project basis, I'll have to handle switching the view to where ever the action took place. For instance, we may be undoing a change in module A while editing module B. In this case, I'll want the user to see the change, so I'll have to switch the view back to module A before undoing the action. Seems like more work to me. Aug 4 at 20:04
  • I think you're right about the user being confused. A single undo and redo stack for the project seems better. I'll wait and see if anyone has more to say before moving forward though. Aug 4 at 20:12

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