/// <summary>
 ///  设置当前项
 /// </summary>
 public void SetCurItem(ImageItem curItem)
 {
     _curItem = curItem;
     if (!_inited && _loaded)
     {
         Init();
     }
 }
        /// <summary>
        /// 当前项变化
        /// </summary>
        private void SelectionChanged(int newIndex, int oldIndex)
        {
            var old = _images.IndexOf(_curItem);
            if (old == newIndex || newIndex == -1) return;
            int start = -1, end = -1;
            if (old > newIndex)
            {
                start = newIndex;
                end = old;
            }
            else
            {
                start = old;
                end = newIndex;
            }

            for (int i = start; i < end; i++)
            {
                GotoPreOrNext(newIndex > old);
            }
            _curItem = _images[newIndex];
        }