UGUI ScrollRect实现带按钮翻页支持拖拽

using UnityEngine;
using System.Collections;
using UnityEngine.UI;
using UnityEngine.EventSystems;
using System.Collections.Generic;
using System;
/// <summary>
/// 略知CSharp 
/// </summary>
public class ScrollRectHelper : MonoBehaviour, IBeginDragHandler, IEndDragHandler
{
 
 public float smooting = 5;    //滑动速度
 public List<GameObject> listItem;   //scrollview item 
 public int pageCount = 3;    //每页显示的项目
 
 ScrollRect srect;
 float pageIndex;     //总页数
 bool isDrag = false;    //是否拖拽结束
 List<float> listPageValue = new List<float> { 0 }; //总页数索引比列 0-1
 float targetPos = 0;    //滑动的目标位置
 float nowindex = 0;     //当前位置索引
 
 void Awake()
 {
 srect = GetComponent<ScrollRect>();
 ListPageValueInit();
 }
 
 //每页比例
 void ListPageValueInit()
 {
 pageIndex = (listItem.Count / pageCount)-1;
 if (listItem != null && listItem.Count != 0)
 {
  for (float i = 1; i <= pageIndex; i++)
  {
  listPageValue.Add((i / pageIndex));
  }
 }
 }
 
 void Update()
 {
 if (!isDrag)
  srect.horizontalNormalizedPosition = Mathf.Lerp(srect.horizontalNormalizedPosition, targetPos, Time.deltaTime * smooting);
 }
 /// <summary>
 /// 拖动开始
 /// </summary>
 /// <param name="eventData"></param>
 public void OnBeginDrag(PointerEventData eventData)
 {
 isDrag = true;
 }
 /// <summary>
 /// 拖拽结束
 /// </summary>
 /// <param name="eventData"></param>
 public void OnEndDrag(PointerEventData eventData)
 {
 isDrag = false;
 var tempPos = srect.horizontalNormalizedPosition; //获取拖动的值
 var index = 0;
 float offset = Mathf.Abs(listPageValue[index] - tempPos); //拖动的绝对值
 for (int i = 1; i < listPageValue.Count; i++)
 {
  float temp = Mathf.Abs(tempPos - listPageValue[i]);
  if (temp < offset)
  {
  index = i;
  offset = temp;
  }
 }
 targetPos = listPageValue[index];
 nowindex = index;
 }
 
 public void BtnLeftGo()
 {
 nowindex = Mathf.Clamp(nowindex - 1, 0, pageIndex);
 targetPos = listPageValue[Convert.ToInt32(nowindex)];
 }
 
 public void BtnRightGo()
 {
 nowindex = Mathf.Clamp(nowindex + 1, 0, pageIndex);
 targetPos = listPageValue[Convert.ToInt32(nowindex)];
 
 }
}