inventory/Runtime/UI/DragAndDropItem.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;
using Sirenix.OdinInspector;
using KairoEngine.UI;

namespace KairoEngine.Inventory
{
    // Todo: Fix droping items on the ground

    public class DragAndDropItem : MonoBehaviour
    {

        public GraphicRaycaster m_Raycaster;
        public EventSystem m_EventSystem;
        
        public Image itemCursorImage;

        private PointerEventData m_PointerEventData;

        private ItemSlotUi previousItemSlot;
        private bool isDragging = false;
        private ItemRef itemRef;

        private List<RaycastResult> results;

        void Update()
        { 
            if (MouseInputUIBlocker.BlockedByUI == true)
            {
                ItemSlotUi targetItemSlot = RaycastSlot();
                if(targetItemSlot != null)
                {
                    // Start Draging item from itemslot
                    if(!isDragging && Input.GetButtonDown("Fire1") && targetItemSlot.draggable)
                    {
                        isDragging = true;
                        previousItemSlot = targetItemSlot;
                        itemRef = previousItemSlot.itemRef;
                        previousItemSlot.parentItemContainer.RemoveItem(itemRef);
                        itemCursorImage.sprite = itemRef.item.icon;
                        itemCursorImage.gameObject.SetActive(true);
                        itemCursorImage.transform.position = new Vector3(Input.mousePosition.x, Input.mousePosition.y, 0);
                    }
                    // Release item on itemslot
                    if(isDragging && Input.GetButtonUp("Fire1"))
                    {
                        isDragging = false;
                        itemCursorImage.gameObject.SetActive(false);
                        if(targetItemSlot.itemRef == null && targetItemSlot.dropable)
                        {
                            targetItemSlot.parentItemContainer.AddItem(itemRef);
                        }
                        else
                        {
                            previousItemSlot.parentItemContainer.AddItem(itemRef);
                        }
                    }
                }
                else
                {
                    // Check ui raycast results
                    if(results.Count > 0)
                    {
                        // Item droped somewhere else in the ui
                        if(isDragging && Input.GetButtonUp("Fire1"))
                        {
                            isDragging = false;
                            previousItemSlot.parentItemContainer.AddItem(itemRef);
                            itemCursorImage.gameObject.SetActive(false);
                        }
                    }
                    else
                    {
                        if(isDragging && Input.GetButtonUp("Fire1"))
                        {
                            isDragging = false;
                            itemCursorImage.gameObject.SetActive(false);
                            // ! Fix when dependencies are solved
                            //ICommand dropItemCommand = new DropItemCommand(previousItemSlot.parentItemContainer, itemRef);
                            //CommandInvoker.AddCommand(dropItemCommand);
                        }
                    }
                    
                }
            }
            // Release item on ground
            
            // Update Dragged item's icon image position
            if (isDragging && Input.GetButton("Fire1"))
            {
                itemCursorImage.transform.position = new Vector3(Input.mousePosition.x, Input.mousePosition.y, 0);
            }
        }

        private ItemSlotUi RaycastSlot()
        {
            //Set up the new Pointer Event
            m_PointerEventData = new PointerEventData(m_EventSystem);
            //Set the Pointer Event Position to that of the mouse position
            m_PointerEventData.position = Input.mousePosition;
            //Create a list of Raycast Results
            results = new List<RaycastResult>();
            //Raycast using the Graphics Raycaster and mouse click position
            m_Raycaster.Raycast(m_PointerEventData, results);
            //For every result returned, output the name of the GameObject on the Canvas hit by the Ray
            foreach (RaycastResult result in results)
            {
                ItemSlotUi slot = result.gameObject.GetComponent<ItemSlotUi>();
                if (slot != null)
                {
                    // Hovering a item slot
                    if(slot.itemRef == null)
                    {
                        //Debug.Log("Hovering empty item slot " + slot.name);
                    }
                    else
                    {
                        //Debug.Log("Hovering item " + slot.itemRef.item.name);
                    }
                    return slot;
                }
            }
            return null;
        }
    }
}