unity – How can I check if object exist in a list and if not to add it to the list?

if (transform.GetComponent<InteractableItem>() == null)
            {
                InteractableItem interactableNaviItem = transform.gameObject.AddComponent<InteractableItem>();
                for (int i = 0; i < ikControl.lookObjs.Count; i++)
                {
                    if(ikControl.lookObjs(i).contains)
                    ikControl.lookObjs.Add(interactableNaviItem);
                }
                interactableNaviItem.interactableMode = InteractableItem.InteractableMode.ActionWithoutThrow;
                interactableNaviItem.distance = 1.7f;
            }

At this line there is no contains property :

if(ikControl.lookObjs(i).contains)

The List definition :

public List<InteractableItem> lookObjs = new List<InteractableItem>();

The type is of this class :

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.Events;
using System;

public class InteractableItem : MonoBehaviour
{
    public string currentMode;

    public enum InteractableMode
    {
        Description,
        Action,
        ActionWithoutThrow
    };

    public InteractableMode interactableMode = InteractableMode.Description;
    public float distance;

    (TextArea(1, 10))
    public string description = "";

    public bool IsAnyAction()
    {
        return interactableMode == InteractableMode.ActionWithoutThrow || interactableMode == InteractableMode.Action;
    }

    public bool IsActionWithoutThrow()
    {
        return interactableMode == InteractableMode.ActionWithoutThrow;
    }

    private void Start()
    {
        currentMode = GetComponent<InteractableItem>().interactableMode.ToString();
    }

    private void Update()
    {
        
    }
}