[C#] Problem with variable reference in List

Questions & Answers
1

I have a small problem with my script. I declare an int variable testInt, then create a List and add the testInt variable to it. This should create a reference, right? However, when I change the value of the variable inside the list, it only changes that variable’s value, and not the original testInt :frowning:
What am I doing wrong?

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

public class Test : MonoBehaviour {
     public int testInt = 1;

     void Start() {
          TestFunction();
     }

     void TestFunction() {
          List<int> testList = new List<int>();
          testList.Add(testInt);

          for(int i = 0; i < testList.Count; i++) {
               testList *++;*

Debug.Log("testInt: " + testInt + ", testList_: " + testList*);
//prints "“testInt: 1, testList[0]: 2”
//SHOULD print "“testInt: 2, testList[0]: 2”
}
}
}*_

2

Why should it? An int is not a reference type, but a value type. It is copied into the list when you add it. If you want the class field to change, you’ll have to encapsulate it in a reference type and add that reference to the list.

For example:

public class ValueWrapper<T>
	{
		public ValueWrapper(T value)
		{
			Value = value;
		}

		public T Value;
	}

	public class TestReferenceList : MonoBehaviour
	{
		public ValueWrapper<int> TestInt = new ValueWrapper<int>(1);

		public List<ValueWrapper<int>> TestList;

		void Start()
		{
			TestFunc();
		}

		void TestFunc()
		{
			TestList = new List<ValueWrapper<int>>();
			TestList.Add(TestInt);

			for (int i = 0; i < TestList.Count; i++)
			{
				TestList*.Value++;*

_ Debug.Log("Class field: " + TestInt.Value + ", list element: " + TestList*.Value);_
_ // prints Class field: 2, list element: 2*_
* }*
* }*
* }*
EDIT: it’s also doable with reflection, where you add the [FieldInfo][1] to the list, but that’s usually not cost-effective.
_*[1]: Microsoft Learn: Build skills that open doors in your career