EquipmentManager.cs

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

public class EquipmentManager : MonoBehaviour {

    #region Singleton
    public static EquipmentManager instance;

    void Awake()
    {
        instance = this;
    }
    #endregion

    Equipment[] currentEquipment;

    public delegate void OnEquipmentChanged(Equipment newItem, Equipment oldItem);
    public OnEquipmentChanged onEquipmentChanged;

    Inventory inventory;

    private void Start()
    {
        inventory = Inventory.instance;
        int numSlots = System.Enum.GetNames(typeof(EquipmentSlot)).Length;
        currentEquipment = new Equipment[numSlots];
    }

    public void Equip (Equipment newItem)
    {
        int slotIndex = (int)newItem.equipSlot;

        Equipment oldItem = null;

        if(currentEquipment[slotIndex] != null)
        {
            oldItem = currentEquipment[slotIndex];
            inventory.Add(oldItem);
        }
        
        if(onEquipmentChanged != null)
        {
            onEquipmentChanged.Invoke(newItem, oldItem);
        }

        currentEquipment[slotIndex] = newItem;
    }

    public void Unequip(int slotIndex)
    {
        if (currentEquipment[slotIndex] != null)
        {
            Equipment oldItem = currentEquipment[slotIndex];
            inventory.Add(oldItem);

            currentEquipment[slotIndex] = null;

            if (onEquipmentChanged != null)
            {
                onEquipmentChanged.Invoke(null, oldItem);
            }

        }

    }
        public void UnequipAll()
        {
            for (int i = 0; i<currentEquipment.Length; i++)
            {
                Unequip(i);
            }
        }

    private void Update()
    {
        if (Input.GetKeyDown(KeyCode.U))
        {
            UnequipAll();
        }
    }

}