Undo and Redo: Approaches to Action Logging

The undo and redo features are ubiquitous in modern software, appearing across a wide range of applications. Their integration has become essential, yet users often encounter challenges with these features, such as issues determining the extent of an action to undo or difficulties in redoing an action after an undo operation.

In my current freelance project, a web-based graphical editing tool, I am exploring efficient implementations of undo and redo functionality. Ensuring that these features meet user expectations and operate smoothly is crucial for the success of the application. To this end, I have considered various strategies for managing undo and redo actions. Below, I outline three different approaches, including a novel combination of two existing methods.

Method A: Comprehensive Logging

In Method A, every action performed by the user is logged in its entirety. This approach includes the following data for each action:

• OBJECT: The object affected by the action
• ACTION: The type of action performed
• POST_DATA: The state of the object after the action
• PRESENT_DATA: The state of the object before the action

Pros:

• Every action can be undone, regardless of how minor it was. This provides a high level of granularity and flexibility for the user.

Cons:

• The approach requires substantial memory to store each action individually, which can be inefficient.
• Users may need to repeatedly click the undo button to revert to a desired state, potentially leading to frustration.

Method B: Action Consolidation

Method B introduces a rule to reduce redundancy by consolidating sequential actions that affect the same object in the same way:

• Rule: If the most recent action and the present action both affect the same object and are of the same type, update the existing log entry with the new data. Otherwise, log the present action as a new record.

Pros:

• Users can easily undo a sequence of actions up to a specific point, reducing the need to repeatedly click the undo button.

Cons:

• This method does not support undoing actions that are interspersed with other actions, limiting flexibility.

Method C: Hybrid Approach (Method A+B)

Method C combines elements of both Method A and Method B to balance granularity and efficiency:

• Rule: Introduce a sensitivity threshold to determine when to consolidate actions versus creating a new log entry. For example:
  • Sensitivity: 5
  • If the difference between the present_data of the last logged action and the present_data of the present action is greater than the sensitivity value, log the present action as a new record. Otherwise, update the existing log entry.

Pros:

• This hybrid method reduces memory usage by consolidating similar actions while maintaining the ability to undo actions with sufficient granularity.
• It enhances user experience by minimizing unnecessary undo clicks and managing memory more efficiently.

Cons:

• The effectiveness of this method depends on selecting an appropriate sensitivity value, which may require fine-tuning based on the specific application and user behavior.

In summary, each method offers distinct advantages and limitations. Method A provides comprehensive logging at the expense of memory usage, Method B optimizes the user experience by consolidating actions but lacks flexibility, and Method C aims to combine the strengths of both approaches. Choosing the right method depends on the application’s requirements and user expectations.