Altering list error

Unity Engine
,
1

So I’m iterating through a list and adding values to different lists and once I’ve gone through it completely I clear the list and continue. I’m still getting an error however that after googling appears to be about altering lists whilst using them.

private void Awake()
    {
        generatePlanets();
      
    }

    void Start()
    {
        planetPositions = new List<Vector2>();
        lastCirclesPlanets = new List<Vector2>();
    }

    // Update is called once per frame
    void Update()
    {

    }

    private void OnDrawGizmos()
    {
        generateCircles(amountOfCircles);
        drawPlanets();
      
    }

    void generateCircles(int amountOfCircles)
    {
        for (int i = 0; i < amountOfCircles; i++)
        {
            Gizmos.DrawWireSphere(this.transform.position, firstCircleRadius * i + 1);
        }
    }

    void generatePlanets()
    {
        //Add starting planet
        planetPositions.Add(new Vector2(this.transform.position.x, this.transform.position.y));
        lastCirclesPlanets = planetPositions;
        for (int i = 0; i < amountOfCircles; i++)
        {
            currentCircle = i;
            List<Vector2> tempList = new List<Vector2>();
            tempList = lastCirclesPlanets;
            foreach (Vector2 planet in tempList)
            {
                findNewPlanetPosition(planet, newPlanetsPerCircle);
            }
            lastCirclesPlanets.Clear();
            lastCirclesPlanets = currentCirclesPlanets;
            currentCirclesPlanets.Clear();
        }
      
    }

    void drawPlanets()
    {
        foreach (Vector2 planet in planetPositions)
        {
            Gizmos.DrawSphere(planet, planetSize);
        }
    }

    void findNewPlanetPosition(Vector2 planetPosition, int newPlanets)
    {
        for (int i = 0; i < newPlanets;)
        {
            for (int j = 0; j < failSafeAttempts; j++)
            {

                Vector2 angle = Random.insideUnitCircle.normalized;
                Vector2 newPosition = planetPosition;
                newPosition += (angle * firstCircleRadius) + new Vector2(Random.Range(-1, 2), Random.Range(-1, 2));
                //newPosition += (angle * firstCircleRadius);
                if (!validateNewPlanet(newPosition)) { }
                else
                {
                    currentCirclesPlanets.Add(newPosition);
                    planetPositions.Add(newPosition);
                    j = 300;
                }
            }

            i++;
        }
    }

    bool validateNewPlanet(Vector2 newPlanetPosition)
    {
        //(x-centerpoint.x)^2 + (y-centerpoint.y)^2 < radius^2
        if (Mathf.Pow(newPlanetPosition.x, 2) + Mathf.Pow(newPlanetPosition.y, 2) < Mathf.Pow(firstCircleRadius * (currentCircle + 1), 2) && !(Mathf.Pow(newPlanetPosition.x, 2) + Mathf.Pow(newPlanetPosition.y, 2) < Mathf.Pow(firstCircleRadius * (currentCircle), 2)))
        {
            return true;
        }
        return false;
    }

and the error code it came with:
InvalidOperationException: Collection was modified; enumeration operation may not execute.
System.Collections.Generic.List1+Enumerator[T].MoveNextRare () (at <9aad1b3a47484d63ba2b3985692d80e9>:0) System.Collections.Generic.List1+Enumerator[T].MoveNext () (at <9aad1b3a47484d63ba2b3985692d80e9>:0)
GenerateUniverse.generatePlanets () (at Assets/Scripts/Mathijs_Scripts/Generate Universe/Attempt 2/GenerateUniverse.cs:64)

I’ve also attempted making the list into an array (tempList.ToArray()) but when I do this it won’t execute the code completely

If anyone can help me out see what I’m doing wrong that would be great!

2

You have a lot of very odd things going on, but one thing I see is perhaps a misunderstanding of reference types and how it works with list.

I feel like you’ve got a lot of very odd bits of code. But one thing that stands out is you have the list planetPositions and you set lastCiclesPlanets equal to this list. And then you set tempList equal to lastCirclesPlanets. In the end, these are all a reference to the same list. What that essentially means is anything done to one of those list is actually modifying the same list for all of them. So adding or calling clear on one affects them all.

What you might actually want is to clone a list instead if you are wanting to keep the same elements but actually have 2 different list.

Because right now, in your generatePlanets method you have tempList == lastCirclesPlanets == planetPosition which means all three list are the same list in memory.

3

That explains a lot!
How would I go about making a clone of the list instead of a reference as I have been doing?

4

Usually just with the constructor that takes another collection: List<T> listB = new List<T>(listA);

5

It seems to be working now, Thanks!