UI设计

把物品挂载在 Box 下即可
UI总结，设置完成后只能实现响应的UI，缺少分页（由代码控制）等功能

代码设计

代码实现思路：

由滚动区域的horizontalNormalizedPosition控制位置，当滚动位于最左边时horizontalNormalizedPosition == 0，而位于最右边时为horizontalNormalizedPosition == 1。

1. 计算背包页数
2. 计算存储每一页horizontalNormalizedPosition的值
3. 比较当前存储的值与释放（停止拖动）时的大小判断为左拖动还是右拖动
4. 计算处与停止拖动时 horizontalNormalizedPosition距离最近的值，通过Update lerp取值，把horizontalNormalizedPosition设置为最近的值

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具体代码（继承IBeginDragHandler,IEndDragHandler接口），挂载在 Knapsack 下

public class KnapsackPage : MonoBehaviour, IBeginDragHandler, IEndDragHandler
{
   public static KnapsackPage _instance; 
   public ScrollRect rect;
   public Text pageInfo;
   public float[] index;
   public float smooth = 5.0f;

   public Transform[] boxes;
   public GameObject itemPref;

   private RectTransform view, content;
   private bool isDrag;
   private int pageIndex = 0;

   void Awake()
   {
       _instance = this;
   }
   void Start()
   {
	   //计算页数以及对应的 horizontalNormalizedPosition 值
       view = this.transform.Find("View").GetComponent<RectTransform>();
       content = this.transform.Find("View/Content").GetComponent<RectTransform>();
       float pages = content.childCount / 20.0f;
       float step = 1.0f / (pages - 1);
       index = new float[(int)(pages)];
       index[0] = 0;
       for (int i = 1; i < pages; i++)
       {
           index[i] = index[i - 1] + step;
       }
       pageInfo.text = (pageIndex + 1).ToString() + "/" + ((int)pages).ToString();
       isDrag = false;
   }
   public void OnBeginDrag(PointerEventData eventData)
   {
       isDrag = true;
   }

   public void OnEndDrag(PointerEventData eventData)
   {
       //向左拉， pageindex增加
       if (index[pageIndex] > rect.horizontalNormalizedPosition)
       {
           pageIndex = pageIndex + 1 >= index.Length ? index.Length - 1 : pageIndex + 1;
       }
       else
       {
           pageIndex = pageIndex - 1 < 0 ? 0 : pageIndex - 1;
       }
	   //计算释放时最近的页数对应的 horizontalNormalizedPosition
       float minDis = Mathf.Abs(index[pageIndex] - rect.horizontalNormalizedPosition);
       for (int i = 0; i < index.Length; i++)
       {
           if (minDis > Mathf.Abs(index[i] - rect.horizontalNormalizedPosition))
          {
               minDis = Mathf.Abs(index[i] - rect.horizontalNormalizedPosition);
               pageIndex = i;
           }
       }
       isDrag = false;
   }
   public void OnLeftBtnClicked()
   {
       pageIndex = pageIndex - 1 < 0 ? 0 : pageIndex - 1;
   }
   public void OnRightBtnClicked()
   {
       pageIndex = pageIndex + 1 >= index.Length ? index.Length - 1 : pageIndex + 1;
   }
   void Update()
   {
	   //插值运算，达到缓动的目的
       if (isDrag == false && Mathf.Abs(rect.horizontalNormalizedPosition - index[pageIndex]) > 0.0015f)
       {
           rect.horizontalNormalizedPosition = Mathf.Lerp(rect.horizontalNormalizedPosition, index[pageIndex],
               Time.deltaTime * smooth);
           if (Mathf.Abs(rect.horizontalNormalizedPosition - index[pageIndex]) < 0.0015f)
           {
               rect.horizontalNormalizedPosition = index[pageIndex];
               pageInfo.text = (pageIndex + 1).ToString() + "/" + ((int)index.Length).ToString();
           }
       }
   }

做完上面这些基本就差不多了，但是，拖动的时候会出现 Box 挡住物体的情况，这是由于层级关系的影响，所以我的解决思路就是拖动物体时更改父级节点。

---

物品拖动以及更改父级节点，挂载在 Box下的物体中 下

public class ItemController : MonoBehaviour, IDragHandler, IBeginDragHandler, IEndDragHandler, IPointerClickHandler
{
   [HideInInspector]
   public Transform parent;

   public Text num;
   private Transform grandParent;

   void Start()
   {
   }
   public void UpdateImageShow()
   {
       ItemInfoController info = GetComponent<ItemInfoController>();
       GetComponent<Image>().sprite = Resources.Load<Sprite>("Textures/" + info.data.itemInfo.iconName);
   }
   public void UpdateNumShow()
   {
       if (GetComponent<ItemInfoController>().data.num <= -1)
       {
           Destroy(transform.gameObject);
       }
       num.text = transform.GetComponent<ItemInfoController>().data.num.ToString();
   }
   public void OnDrag(PointerEventData eventData)
   {
       transform.position = eventData.position;
	   // 取消相对应的射线检测，拖动结束才能检测到底部格子而不被遮挡
       transform.GetComponent<Image>().raycastTarget = false;
   }

   public void OnBeginDrag(PointerEventData eventData)
   {
       parent = transform.parent;
       grandParent = GameObject.Find("Canvas").transform;
       transform.parent = grandParent;
   }

   public void OnEndDrag(PointerEventData eventData)
   {
       if (transform.parent == grandParent)
       {
           transform.parent = parent;
           transform.localPosition = Vector3.zero;
       }
       transform.GetComponent<Image>().raycastTarget = true;
   }
	   // IPointerClickHandler 对应点击事件（OnPointerClick），弹出装备详细信息面板（这里忽略）

---

格子（Box）控制，挂载在 Box 下

public class BoxController : MonoBehaviour, IDropHandler
{
   /// <summary>
   /// 物品被放置的时候
   /// </summary>
   /// <param name="eventData"></param>
   public void OnDrop(PointerEventData eventData)
   {
       //被拖动的物体
       GameObject item = eventData.pointerDrag;
       //被拖动的物体只能是Item，否则不作相应
       if (item.gameObject.tag != Tags.Item)
       {
           return;
       }
       //自身格子，被拖动物体取消射线检测，这里才能检测到
       GameObject box = eventData.pointerCurrentRaycast.gameObject;
       if (box.tag == Tags.Item)
       {
		   //别拖动到存有物体的格子，交换位置
           Transform temp = item.GetComponent<ItemController>().parent;
           item.transform.parent = box.transform.parent;
           box.transform.parent = temp;
           //
           box.transform.localPosition = Vector3.zero;
           item.transform.localPosition = Vector3.zero;
       }
       else if(box.tag == Tags.Box)
       {
		   //别拖动到空格子，设置位置
           item.transform.parent = transform;
           item.GetComponent<RectTransform>().localPosition = Vector3.zero;
       }
   }
}

以上便实现了一个背包系统，支持拖拽，交换，分页等功能