Scriptum/Assets/Scripts/Item/ItemSlot.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using TMPro;
using UnityEngine.UI;
using UnityEngine.EventSystems;
using System;   // for Action type

public class ItemSlot : MonoBehaviour, ISlot, IBeginDragHandler, IEndDragHandler, IDragHandler, IDropHandler
{
    [Header("UI Stuff to change")]
    [SerializeField] private TextMeshProUGUI slotItemNumberText;
    [SerializeField] private Image itemImage;

    public BasePanelController _PanelController;

    private Color normalColor = Color.white;
    private Color disabledColor = new Color(1, 1, 1, 0); // transparency = 0

    [Header("Slot variable")]
    [SerializeField]
    protected int _number;
    public int Number {
        get { return _number; }
        set {
            _number = value;
        }
    }
    [SerializeField]
    protected Item _item;
    public Item Item {
        get { return _item; }
        set {
            _item = value;

            if(_item == null) {
                itemImage.color = disabledColor;
            } else {
                itemImage.sprite = _item.Image;
                itemImage.color = normalColor;
            }
        }
    }
    public int countStackableItems = 0;

    public event Action<ItemSlot> OnBeginDragEvent;
    public event Action<ItemSlot> OnEndDragEvent;
    public event Action<ItemSlot> OnDragEvent;
    public event Action<ItemSlot> OnDropEvent;

    public void SetupSlot(int _number, Item _item, BasePanelController _PanelController)
    {
        this._PanelController = _PanelController;

        Number = _number;

        if(_item)
        {
            SetItem(_item);
        }
    }

    public void SetItem(Item _item)  // dont change slot numer after assign new item, numbers are bind during object init
    {
        Item = _item;

        ChangeEnableImageView(true);

        countStackableItems +=1;

        UpdateItemNumberHolder();
    }
        

    private void ChangeEnableImageView(bool _flag)
    {
        itemImage.color = _flag ? normalColor : disabledColor; //!slotImage.enabled;
    }

    private void ChangeNumberHeldView(bool _flag)
    {
        slotItemNumberText.enabled = _flag;
    }

    private void UpdateItemNumberHolder()
    {
        slotItemNumberText.text = "" + countStackableItems;
    }

    // Start is called before the first frame update
    void Start()
    {
        if(!Item)
        {
            ChangeEnableImageView(false);
            ChangeNumberHeldView(false);
        }
    }

    public virtual bool CanReceiveItem(Item item)
    {
        return true;
    }

    // Events methods
    public void OnBeginDrag(PointerEventData eventData)
    {
        if(OnBeginDragEvent != null)
            OnBeginDragEvent(this);
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        if(OnEndDragEvent != null)
            OnEndDragEvent(this);
    }

    public void OnDrag(PointerEventData eventData)
    {
        if(OnDragEvent != null)
            OnDragEvent(this);
    }

    public void OnDrop(PointerEventData eventData)
    {
        if(OnDropEvent != null)
            OnDropEvent(this);
    }
}