无法从列表中删除元素

Question

I'm developing a game in Unity, and I want to remove an element from a list. But when I call the method List<T>.Remove(T) , it doesn't remove anything.

private void OnMouseDown()
{
    Debug.Log("Clicked for mixing");
    foreach (Element element in ElementsControl.elements)
    {
        if (element.composition.Length > 1)
        {
            Debug.Log("FINE. Element is not pure");
            List<Element> a = new List<Element>();
            foreach (Element compElement in element.getRawComposition())
            {
                a.Add(compElement);
            }
            string allComposition = "";
            foreach (Element dispElement in a)
            {
                if (allComposition == "")
                    allComposition = dispElement.name;
                else
                    allComposition += " + " + dispElement.name;
            }
            Debug.Log(element.name + " composition is: " + allComposition);
            string cauldElements = "";
            foreach (Element cauldElem in cauldron.getElements())
            {
                if (cauldElements == "")
                    cauldElements = cauldElem.name;
                else
                    cauldElements += " + " + cauldElem.name;
            }
            Debug.Log("Cauldron has: " + cauldElements);
            if (ContainsAllItems(cauldron.getElements(), a))
            {
                Debug.Log("OK. Mix result is " + element.name + ", used " + a);
                Debug.Log("Removing " + a.Count + " elements from cauldron");
                int counter = 0;
                foreach (Element remElem in a)
                {
                    cauldron.getElements().Remove(remElem);
                    Debug.Log("Removed " + remElem + " from cauldron");
                    counter++;
                }
                Debug.Log("Removed " + counter + " elements from cauldron");
                Debug.Log("Adding " + element + " to cauldron");
                cauldron.getElements().Add(element);
                return;
            }
            else
                Debug.Log("NO. Mix result not ok");
        }
    }
}

The problem comes in these lines:

foreach (Element remElem in a)
{
  cauldron.getElements().Remove(remElem);
  Debug.Log("Removed " + remElem + " from cauldron");
  counter++;
}

When I try to delete it, the list stays as it, without deleting anything.

Answer 1

You can't delete anything because remElem is reference in a but you delete it from another list. Even if objects has same values, the references are different. There is no reference equal to remElem in cauldron.getElements() .

You should write some query to do it:

cauldron.getElements().RemoveAll((e) => e.Id == remElem.Id); // or other field or fields

You should find object that has same values as remElem in cauldron.getElements() and then delete it from that list.

But it deletes all elements.

To delete only one you should do:

var list = cauldron.getElements();
foreach (Element remElem in a)
{
    var elems = list.Where((e) => e.Id == remElem.Id);
    if (elems.Any())
    {
        list.Remove(elems.ElementAt(0));
        Debug.Log("Removed " + remElem + " from cauldron");
        counter++;
    }
}