rua/Script/InventoryScripts/ItemOnDrag.cs

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

public class ItemOnDrag : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
    public Transform originalParent; // 记录原先的父级
    public Inventory myBag;
    public Slot slot;
    public int currentItemIndex; // 当前被拖拽物品的下标

    public void OnBeginDrag(PointerEventData eventData)
    {
        originalParent = transform.parent;
        currentItemIndex = originalParent.GetComponent<Slot>().slotIndex;
        transform.SetParent(transform.parent.parent); // 避免拖拽时物品被遮挡
        transform.position = eventData.position;
        GetComponent<CanvasGroup>().blocksRaycasts = false;
    }

    public void OnDrag(PointerEventData eventData)
    {
        transform.position = eventData.position;
        // Debug.Log(eventData.pointerCurrentRaycast.gameObject.name);
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        // 如果将物品移动到背包内，则改变位置
        if (eventData.pointerCurrentRaycast.gameObject != null)
        {
            // 如果格子中有物品，则交换位置
            if (eventData.pointerCurrentRaycast.gameObject.name == "Item Image") 
            {
                // 交换物品在背包中显示的位置
                transform.SetParent(eventData.pointerCurrentRaycast.gameObject.transform.parent.parent);
                transform.position = eventData.pointerCurrentRaycast.gameObject.transform.parent.parent.position;
                
                // 交换物品在背包中的下标
                var temp = myBag.itemList[currentItemIndex];
                myBag.itemList[currentItemIndex] = myBag.itemList[eventData.pointerCurrentRaycast.gameObject.GetComponentInParent<Slot>().slotIndex];
                myBag.itemList[eventData.pointerCurrentRaycast.gameObject.GetComponentInParent<Slot>().slotIndex] = temp;

                eventData.pointerCurrentRaycast.gameObject.transform.parent.position = originalParent.transform.position;
                eventData.pointerCurrentRaycast.gameObject.transform.parent.SetParent(originalParent);
                GetComponent<CanvasGroup>().blocksRaycasts = true; // 开启射线阻挡，否则无法再次选中移动的物品
            }
            
            // 如果格子中没有物品，则将物品放至此位置
            else if (eventData.pointerCurrentRaycast.gameObject.name == "Slot(Clone)")
            {
                // 改变物品在背包中显示的位置
                transform.SetParent(eventData.pointerCurrentRaycast.gameObject.transform); 
                transform.position = eventData.pointerCurrentRaycast.gameObject.transform.position;
            
                // 改变物品在背包中的下标
                myBag.itemList[eventData.pointerCurrentRaycast.gameObject.GetComponentInParent<Slot>().slotIndex] = myBag.itemList[currentItemIndex];
                if (eventData.pointerCurrentRaycast.gameObject.GetComponent<Slot>().slotIndex != currentItemIndex)
                    myBag.itemList[currentItemIndex] = null; // 如果放回原处则不执行该句，避免放回原处后物品消失

                GetComponent<CanvasGroup>().blocksRaycasts = true; // 开启射线阻挡，否则无法再次选中移动的物品
            }
            
            // 如果移到格子外 ，则物品自动回到原来的位置
            else
            {
                transform.SetParent(originalParent);
                transform.position = originalParent.position;
                GetComponent<CanvasGroup>().blocksRaycasts = true; // 开启射线阻挡，否则无法再次选中移动的物品
            }
        }
        
        // 如果移到背包外，则物品自动回到原来的位置
        else
        {
            // 物品回到初始位置
            transform.SetParent(originalParent);
            transform.position = originalParent.position;
            GetComponent<CanvasGroup>().blocksRaycasts = true; // 开启射线阻挡，否则无法再次选中移动的物品
        }
    }        
}