Command History

Command-base history service

In One Line

Time-travel for your actions: Command, undo, redo, perfect!

Package Info

display name	AceLand Kalman Filter
package name	com.aceland.commandhistory
latest version	1.1.1
namespace	AceLand.CommandHistory
git repository	https://github.com/parsue/com.aceland.commandhistory.git
dependencies	com.aceland.library: 2.0.11 com.aceland.eventdriven: 2.1.8

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Project Settings

Command History	---
Max History	Maximum history to be kept in system. range: 16 to 512 default: 32
Events	---
New History Events	Enable events on new history added default: true
Undo History Events	Enable events on history undone default: true
Redo History Events	Enable events on history redone default: true
Clear History Events	Enable events on history clear default: true
History Change Events	Any above event invoked default: true

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API

// base API
AceCommand

// other properties and functions
AceCommand.Builder;

AceCommand.Undo();
int i = AceCommand.UndoCount();

AceCommand.Redo();
int i = AceCommand.RedoCount();

AceCommand.Clear();

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Overview

Command History is a flexible undo/redo system that helps you track and reverse user actions in your Unity application. Built on the Command pattern, it provides a clean, type-safe way to implement history management for any operation.

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Quick Start

Create Command

create a new command on changing the target value.

int life = 12;

ICommand command = AceCommand.Builder()
    .WithUndoState(() => life += damage)    // restore command
    .WithRedoState(() => life -= damage)    // execute command
    .Build();

Execute

Undo and Redo

Clear History

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Events

Events will be raised on certains situations

Event	Description
INewHistoryEvent	On history is added to system. Case including Add() and AddAndExecute().
IUndoHistoryEvent	On history is undone.
IRedoHistoryEvent	On history is redone.
IClearHistoryEvent	On history is clear.
IHistoryChangeEvent	On any above cases are invoked.

Please refer to Event Bus page for the details of events.

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Example

Logics

using AceLand.CommandHistory;
using UnityEngine;

public class PlayerLife : MonoBehaviour
{
    // target value
    [SerializeField] private int life = 12;
    
    // on damage
    private void Damage(int damage = 3)
    {
        life -= damage;
    
        var command = AceCommand.Builder()
            .WithUndoState(() => life += damage)
            .WithRedoState(() => life -= damage)
            .Build();
            
        // damage has been executed, Add only
        command.Add();
    }

    // on heal
    private void Heal(int heal = 2)
    {
        var command = AceCommand.Builder()
            .WithUndoState(() => life -= heal)
            .WithRedoState(() => life += heal)
            .Build();
            
        // heal has not been executed, Add And Execute
        command.AddAndExecute();
    }
}

History UI

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Common Patterns

Basic Command Creation

// Method 1: Using Builder Pattern
var command = AceCommand.Builder()
    .WithRedoState(() => { /* do something */ })
    .WithUndoState(() => { /* undo something */ })
    .Build();

// Method 2: Implementing ICommand
public class MoveObjectCommand : ICommand
{
    private readonly Transform target;
    private readonly Vector3 newPos;
    private readonly Vector3 oldPos;

    public MoveObjectCommand(Transform target, Vector3 newPosition)
    {
        this.target = target;
        this.newPos = newPosition;
        this.oldPos = target.position;
    }

    void ICommand.Redo() => target.position = newPos;
    void ICommand.Undo() => target.position = oldPos;
}

Command Management

// Execute immediately and add to history
command.AddAndExecute();

// Add to history without executing
command.Add();

// Check history status
Debug.Log($"Undo steps available: {AceCommand.UndoCount()}");
Debug.Log($"Redo steps available: {AceCommand.RedoCount()}");

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Best Practices

1. Keep Commands Small and Focused

2. Store State, Not References

3. Use Command Groups for Complex Operations

4. Catch events for set state of UI components

5. Pick the perfect time to clear history - for example after data saved

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Tips and Tricks

• Use Command.Clone() to create copies of existing commands

• Commands are automatically validated before execution

• History is cleared when entering play mode

• Commands are executed in FIFO (First In, First Out) order

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