借鑑　　https://www.jianshu.com/p/8bfe94822886

using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;
/// <summary>
/// 指令碼掛載到每個可拖拽的Item上面即可
/// </summary>
public class ItemOnDrag : MonoBehaviour, IPointerDownHandler, IPointerUpHandler, IBeginDragHandler, IDragHandler, IEndDragHandler
{
    
 
// 例項化的新item
    public GameObject mNewItem;
    public Transform mNewItemRoot;
    public ScrollRect mScrollRect;
    // 是否按下
    public bool mIsDown = false;
    // 按下與鬆開滑鼠之間的距離
    public float mBorderDis = 0.5f;
    // 總的按下時間
    public float mTotalTime = 1;
    private float mCurTime = 0;
    // 當前滑鼠位置
    public
 
 Vector3 mCurPos;
    // 上一次滑鼠位置
    public Vector3 mPrevPos;
    private NewItemOnDrag mNewDrag;
    void Start()
    {
        mNewItemRoot = GameObject.Find("InfoBoard").transform;
        mScrollRect = GameObject.Find("InfoBoard").GetComponent<ScrollRect>();
    }
    void Update()
    {
        
 
if (mScrollRect == null)
        {

        }

        if (mIsDown)
        {
            mCurTime += Time.deltaTime * 1;
            if (mCurTime >= mTotalTime)
            {
                if (Vector3.Distance(mPrevPos, mCurPos) > mBorderDis)
                {
                    mCurTime = 0f;
                    return;
                }
                mCurTime = 0f;
                mIsDown = false;
                GameObject item = Instantiate(mNewItem);
                item.transform.SetParent(mNewItemRoot);
                item.transform.localScale = Vector3.one;
                mNewDrag = item.GetComponent<NewItemOnDrag>();
                if (mNewDrag == null)
                    mNewDrag = item.AddComponent<NewItemOnDrag>();
                item.transform.position = Input.mousePosition;
            }
        }
    }

    public void OnPointerDown(PointerEventData eventData)
    {
        mNewDrag = null;
        mPrevPos = Input.mousePosition;
        mCurPos = Input.mousePosition;
        mIsDown = true;
    }

    public void OnPointerUp(PointerEventData eventData)
    {
        mPrevPos = Vector3.zero;
        mCurPos = Vector3.zero;
        mIsDown = false;
        mNewDrag = null;
    }

    public void OnBeginDrag(PointerEventData eventData)
    {
        mScrollRect.OnBeginDrag(eventData);
    }

    public void OnDrag(PointerEventData eventData)
    {
        mCurPos = eventData.position;
        if (mNewDrag == null)
            mScrollRect.OnDrag(eventData);
        else
            mNewDrag.transform.position = Input.mousePosition;
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        mNewDrag = null;
        mScrollRect.OnEndDrag(eventData);
    }


}

using UnityEngine;
using UnityEngine.EventSystems;

public class NewItemOnDrag : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
    public void OnBeginDrag(PointerEventData eventData)
    {

    }

    public void OnDrag(PointerEventData eventData)
    {
        transform.position = Input.mousePosition;
    }

    public void OnEndDrag(PointerEventData eventData)
    {

    }
}

用法

將ItemOnDrag掛在每個可拖拽的Item上面即可
　　其中的mNewItem就是Item本身的預設體，mNewItemRoot是ScrollRect元件容器的transform，mScrollRect是ScrollRect元件容器的ScrollRect，但是mNewItemRoot和mScrollRect需要手動關聯

NewItemOnDrag指令碼會自動掛載到新例項化出來的item上的，不要做處理，後期可加入檢測