How to setup undo/redo system during runtime with Unity3D

Question

I'm trying to set up an undo/redo system during runtime and couldn't get my code to work correctly. I have created an undo button, but when I moved my game object and press the undo button, the game object doesn't go back to its original states.

I just wanted to be able to have the end-user undo /redo his lastest action during runtime and not during Editor mode. I have made several attempts and have tried many different scripts but haven't made any progress. Any suggestions?

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class undoit : MonoBehaviour
{
    public class setting
    {
        public GameObject Obj;
        public Vector3 Pos;
        public Quaternion Rot;
        public bool Deleted;

        public void Restore()
        {
            Obj.transform.position = Pos;
            Obj.transform.rotation = Rot;
            Obj.SetActive(Deleted);
        }
        public setting(GameObject g)
        {
            Obj = g;
            Pos = g.transform.position;
            Rot = g.transform.rotation;
            Deleted = g.activeSelf;
        }
    }
    public List<setting> UndoList;

    public void AddUndo(GameObject g)
    {
        setting s = new setting(g);
        UndoList.Add(s);
    }
    public void Undo()
    {
        if (UndoList.Count > 0)
        {
            UndoList[UndoList.Count - 1].Restore();
            UndoList.RemoveAt(UndoList.Count - 1);
        }
    }
    void Start()
    {
        UndoList = new List<setting>();
    }
}

Answer 1

First you need something you can store the relevant data to like e.g.

public struct ObjectState
{
    // The transform this data belongs to
    private Transform transform;

    private Vector3 localPosition;
    private Quaternion localRotation;
    private Vector3 localScale;

    private bool active;

    public ObjectState (GameObject obj)
    {
        transform = obj.transform;
        localPosition = transform.localPosition;
        localRotation = transform.localRotation;
        localScale = transform.localScale;

        active = obj.activeSelf;
    }

    public void Apply()
    {
        transform.localPosition = localPosition;
        transform.localRotation = localRotation;
        transform.localScale = localScale;

        transform.gameObject.SetActive(active);
    }
}

Next I would use a wrapper class to store undo able changes like

public struct UndoableChange
{
    private ObjectState _before;
    private ObjectState _after;

    public UndoableChange (ObjectState before, ObjectState after)
    {
        _before = before;
        _after = after;
    }

    public void Undo()
    {
        _before.Apply();
    }   

    public void Redo()
    {
        _after.Apply();
    }     
}

Or in case you need it for my objects at once you could use lists e.g. something like

public struct UndoableChange
{
    private List<ObjectState> _before;
    private List<ObjectState> _after;

    public UndoableChange (List<ObjectState> before, List<ObjectState> after)
    {
        _before = before;
        _after = after;
    }

    public void Undo()
    {
        foreach(var state in _before)
        {
            state.Apply();
        }
    }   

    public void Redo()
    {
        foreach(var state in _after)
        {
            state.Apply();
        }
    }     
}

Then for the controller I would use two Stack. A Stack is "last in - first out" so exactly what you need. You add new entries using Push and by using Pop you retrieve the last added element and at the same time remove it from the stack. So it would look like

public static class UndoRedo
{
    private static Stack<UndoableChange> undoStack = new Stack<UndoableChange>();
    private static Stack<UndoableChange> redoStack = new Stack<UndoableChange>();

    public static void Undo()
    {
        if(undoStack.Count == 0) return;

        var lastAction = undoStack.Pop();

        lastAction.Undo();

        redoStack.Push(lastAction);
    }

    public static void Redo()
    {
        if(redoStack.Count == 0) return;

        var lastAction = redoStack.Pop();

        lastAction.Redo();

        undoStack.Push(lastAction);
    }

    public static void AddAction(UndoableChange action)
    {
        redoStack.Clear();

        undoStack.Push(action);
    }
}

I dont know how exactly your user interacts with the objects but you now would always do something like

// at some point store the initial values
var before = new ObjectState (selectedGameObject);

//TODO Apply all your changes to the selected object 

// get the new values
var after = new ObjectState (selectedGameObject);

// Log to the history
UndoRedo.AddAction(new UndoableChange(before, after));

or use lists for all selected objects accordingly e.g. simply using Linq

using System.Linq;

...

var before = selectedGameObjects.Select(obj => new ObjectState(obj)).ToList();

//TODO Apply all your changes to all the selected objects 

var after = selectedGameObjects.Select(obj => new ObjectState(obj)).ToList();

UndoRedo.AddAction(new UndoableChange(before, after));

---

Note: Typed on smartphone but I hope the idea gets clear