C# winform treeview 刷新前,记录上次折叠情况,刷新后,恢复到上次情况

 /// <summary>        /// 存储每个节点的状态        /// </summary>        public static Hashtable StoreNodeState = new Hashtable();        /// <summary>        /// 将节点的状态存起来         /// </summary>        /// <param name="fullPath"></param>        /// <param name="isExpend"></param>        public static void AddNodeStateToHashTable(string fullPath, bool? isExpend)        {            if (!StoreNodeState.ContainsKey(fullPath))            {                StoreNodeState.Add(fullPath, isExpend);            }        }        /// <summary>        /// 清空一下hashtable        /// </summary>        public static void ClearStoreNodeState()        {            StoreNodeState.Clear();        }        /// <summary>        /// true:展开；null：选择并展开，false：折叠        /// </summary>        /// <param name="fullPath"></param>        /// <returns></returns>        public static bool? FindNodeStateByFullPath(string fullPath)        {            if (StoreNodeState.ContainsKey(fullPath))            {                return (bool?)StoreNodeState[fullPath];            }            return false;        }        /// <summary>        /// 在刷新前执行这个方法.        /// value为空，说明isSelected而且展开        /// 优化：如果是折叠的，那么不用存储他的子节点了        /// </summary>        /// <param name="treeNode"></param>        public static void ExecStoreNodeState(TreeNode treeNode)        {            if (treeNode.Nodes == null || treeNode.Nodes.Count == 0)                return;            foreach (TreeNode node in treeNode.Nodes)            {                if (node.IsSelected)                {                    AddNodeStateToHashTable(node.FullPath, null);                    if (node.IsExpanded)                    {                        ExecStoreNodeState(node);                        continue;                    }                }                else if (node.IsExpanded)                {                    AddNodeStateToHashTable(node.FullPath, node.IsExpanded);                    ExecStoreNodeState(node);                }                else if (!node.IsExpanded)                {                    AddNodeStateToHashTable(node.FullPath, node.IsExpanded);                    continue;                }            }        }        /// <summary>        /// 刷新后,执行这个方法,恢复到以前状态        /// </summary>        /// <param name="treeNode"></param>        /// <param name="treeView"></param>        public static void SetTreeNodeState(TreeNode treeNode, TreeView treeView)        {            if (treeNode.Nodes == null || treeNode.Nodes.Count == 0)                return;            bool? findFlag = null;            foreach (TreeNode node in treeNode.Nodes)            {                findFlag = FindNodeStateByFullPath(node.FullPath);                if (findFlag == null)                {                    node.ExpandAll();                    treeView.SelectedNode = node;                    continue;                }                else if (findFlag == false)                {                    node.Collapse(true);                    continue;                }                else if (findFlag == true)                {                    node.Expand();                }                SetTreeNodeState(node, treeView);            }        }