簡介：

在進行UI設計的時候，經常會使用Unity中UI提供的ScrollView，類似Android中的ScrollView，在進行圖片預覽，多個翻頁的時候，能實現很好的效果。

該類中根據Unity的EventSystems中拖拽事件，實現對頁碼的滑動監聽，在使用的時候，新建UI--->ScrollView，把該類元件新增到ScrollView上，把對應的content加入該指令碼中的content，調整ScrollView和Content，設定單個滑動頁的寬度，拖拽的閾值，即可監聽到拖拽，如果是動態例項化ScrollView中的child，需設定當前最大頁碼數。SetCurIndex可以實現直接定位到當前頁碼對應的滑動頁，程式碼比較簡單，直接貼出來。

public class ScrollViewListener : MonoBehaviour, IDragHandler, IBeginDragHandler, IEndDragHandler
    {
		//滑動方向
        public enum MoveDirection
        {
            None = 0,
            Left,
            Right,
        }
        public float SingleItemWidth;//單個滑動頁的寬度
        public RectTransform content;//當前ScrollView的Content
        public float DragMinValue = 5f;//拖動過程中允許的最小的拖拽值，低於此值就不算拖拽，不執行翻頁事件
        private MoveDirection direction = MoveDirection.None;
        private int CurIndex = 0;//當前頁碼
        private int MaxIndex = 0;//最大頁碼
        public bool canMove = true;//是否能移動
        private Vector3 originalPos;
        private float maxDeltaX = 0f;//取整個拖動過程中的最大值
        public Action<int> OnPageChange;//對外提供頁碼修改的回撥
		
        /// <summary>
        /// 滑到下一頁
        /// </summary>
        private void MoveToNext()
        {            
            if (direction == MoveDirection.Left)
            {
                if (CurIndex < MaxIndex)
                {                    
                    CurIndex++;
                    canMove = false;
                    content.DOLocalMoveX(content.localPosition.x - SingleItemWidth, 1f).OnComplete(() =>
                    {
                        if (null != OnPageChange)
                        {
                            OnPageChange(CurIndex);
                        }
                        canMove = true;
                    });
                }
            }
            else if (direction == MoveDirection.Right)
            {
                if (CurIndex > 0)
                {
                    CurIndex--;
                    canMove = false;
                    content.DOLocalMoveX(content.localPosition.x + SingleItemWidth, 1f).OnComplete(() =>
                    {
                        if (null != OnPageChange)
                        {
                            OnPageChange(CurIndex);
                        }
                        canMove = true;
                    });
                }
            }
        }
		
        /// <summary>
        /// 設定當前滑動列表的頁數的最大值
        /// </summary>
        /// <param name="max"></param>
        public void SetMaxIndex(int max)
        {
            MaxIndex = max - 1;//最大下標值為頁數減1
        }

        /// <summary>
        /// 設定當前頁
        /// </summary>
        /// <param name="index"></param>
        public void SetCurIndex(int index)
        {
            CurIndex = index;
            float x = content.localPosition.x - SingleItemWidth * CurIndex;
            content.localPosition = new Vector3(x, content.localPosition.y, content.localPosition.z);
        }

        public void ResetPosition()
        {
            content.localPosition = originalPos;
        }
		
        private void Awake()
		{
            CurIndex = 0;
            originalPos = content.localPosition;
        }

        public void OnDrag(PointerEventData eventData)
        {
            if (Mathf.Abs(eventData.delta.x) > maxDeltaX)
            {
                maxDeltaX = Mathf.Abs(eventData.delta.x);
            }
        }

        public void OnBeginDrag(PointerEventData eventData)
        {
            if (eventData.delta.x > 0)
            {
                direction = MoveDirection.Right;
            }
            else if (eventData.delta.x < 0)
            {
                direction = MoveDirection.Left;
            }
            else
            {
                direction = MoveDirection.None;
            }
            if (Mathf.Abs(eventData.delta.x) > maxDeltaX)
            {
                maxDeltaX = Mathf.Abs(eventData.delta.x);
            }
        }

        public void OnEndDrag(PointerEventData eventData)
        {
            if (Mathf.Abs(eventData.delta.x) > maxDeltaX)
            {
                maxDeltaX = Mathf.Abs(eventData.delta.x);
            }
            if (maxDeltaX > DragMinValue)
            {
                //計算下一頁的目的點 然後移動
                if (canMove)
                {
                    MoveToNext();
                }                
            }
            maxDeltaX = 0f;
        }
    }