TreeView 生成最常见的一种编程实现方式就是通过“父子关系递归”生成树，一般是自顶向下递归生成。这种方法的缺陷：“由父节点及子节点”的遍历顺序意味着每个子节点的父节点必须存在，否则将搜索不到，即出现“
断层现象”。
本文在递归原理的基础上，通过调节父节点的层次，解决树结构的断层问题。
一、递归生成树的算法：
#region 加载部门树*****************************************************
DataSet Dept_ds;
/// <summary>
/// 加载部门树
/// </summary>
public void DeptTree(TreeView tvMenu)
{
Dept_ds = myData.GetDept();//执行 "select * from Sys_Department"
DeptTree(tvMenu, 0, (TreeNode)null);
}
/// <summary>
/// 加载部门树
/// </summary>
private void DeptTree(TreeView tvMenu, int ParentID, TreeNode pNode)
{
string nodeId = "DeptID";
string nodeName = "DeptName";
string nodeParent = "DeptParent";
DataView dvTree = new DataView(Dept_ds.Tables[0]);
//过滤nodeParent,得到当前的所有子节点
dvTree.RowFilter = nodeParent + " = " + ParentID;
foreach (DataRowView drv in dvTree)
{
TreeNode newNode = new TreeNode();
newNode.Text = drv[nodeName].ToString().Trim();
newNode.ToolTip = drv[nodeName].ToString().Trim() + "[ID=" + drv[nodeId].ToString().Trim() + "]";
newNode.Value = drv[nodeId].ToString().Trim();
newNode.Target = "user";
newNode.ImageUrl = ImagePath + "menu/dept.gif";
newNode.NavigateUrl = "UserChoose_User.aspx?DeptID=" + drv[nodeId].ToString().Trim();
if (pNode == null)
{ //添加根节点
newNode.SelectAction = TreeNodeSelectAction.SelectExpand;
newNode.Expanded = false;
newNode.PopulateOnDemand = false;
tvMenu.Nodes.Add(newNode);//***注意区别:根节点
DeptTree(null, Int32.Parse(drv[nodeId].ToString().Trim()), newNode);//递归
}
else
{ //?添加子节点
newNode.SelectAction = TreeNodeSelectAction.SelectExpand;
newNode.Expanded = false;
newNode.PopulateOnDemand = false;
pNode.ChildNodes.Add(newNode);//***注意区别:子节点
DeptTree(null, Int32.Parse(drv[nodeId].ToString().Trim()), newNode);//递归
}
}
}
#endregion
二、断层处理原理：
遍历筛选后的数据表newTable，获取每个节点的所有父节点列表(从未经筛选的数据表oldTable中获取)，判断父节点是否完整存在于newTable中。通过依次调整父节点的层次，保证每个节点的最上级父节点最终为根结点。
递归算法性能上是有点影响，对较少的数据处理还是可以的。下面给出具体实现类：
namespace Framework.Helper
{
/// <summary>
/// 树形结构操作帮助类
/// </summary>
public static class TreeHelper
{
#region 重置数据表的父节点, 解决断层问题
/// <summary>
/// 重置数据表的父节点, 解决树形结构的断层问题
/// </summary>
/// <param name="newTable">筛选后的数据表</param>
/// <param name="oldTable">未经筛选的数据表</param>
/// <param name="IDField">节点ID字段</param>
/// <param name="ParentField">父节点ID字段</param>
public static DataTable ResetParent(DataTable newTable, DataTable oldTable, string IDField, string ParentField)
{
//行循环筛newTable
for (int i = 0; i < newTable.Rows.Count; i++)
{
int id = Convert.ToInt32(newTable.Rows[i][IDField]);
int parentID = Convert.ToInt32(newTable.Rows[i][ParentField]);
//获取指定节点在oldTable的所有父节点
string[] arrParent = GetAllParent(id, oldTable, IDField, ParentField).Split(',');
//遍历oldTable中的所有父节点
for (int j = 0; j < arrParent.Length - 1; j++)
{
//判断父节点是否在newTable中
if (HasNode(newTable, IDField, Convert.ToInt32(arrParent[j])))
{
//若在，设置为父节点
newTable.Rows[i][ParentField] = Convert.ToInt32(arrParent[j]);
break;
}
else
{
//不在，设置父节点为0
newTable.Rows[i][ParentField] = 0;
continue;
}
}
///通过这样的调整，若节点node的父节点不再newTable中，就设置node.Parent = node.Parent.Parent,依次类推。
}
return newTable;
}
/// <summary>
/// 判断指定ID的节点是否存在与指定数据表
/// </summary>
public static bool HasNode(DataTable dt, string IDField, int id)
{
DataView dv = new DataView(dt);
dv.RowFilter = IDField + "=" + id;
return (dv.Count > 0) ? true : false;
}
#endregion
#region 获取指定节点的所有父节点
/// <summary>
/// 获取指定节点的所有父节点ID
/// </summary>
/// <param name="ID">指定节点ID</param>
/// <param name="dataTable">数据表</param>
/// <param name="IDField">节点ID</param>
/// <param name="ParentField">父节点ID</param>
/// <returns>字符串,并以逗号隔开</returns>
public static string GetAllParent(int ID, DataTable dataTable, string IDField, string ParentField)
{
string resultParent = "";
GetAllParent(ID, dataTable, IDField, ParentField, ref resultParent);
return resultParent;
}
private static void GetAllParent(int ID, DataTable dataTable, string IDField, string ParentField, ref string resultParent)
{
DataView dv = new DataView(dataTable);
dv.RowFilter = IDField + "=" + ID;
int parentID = 0;
if (dv.ToTable().Rows.Count > 0)//***
parentID = Convert.ToInt32(dv.ToTable().Rows[0][ParentField]);
resultParent += parentID + ",";
if (parentID > 0)
{
GetAllParent(parentID, dataTable, IDField, ParentField, ref resultParent);
}
}
#endregion
}
}
三、如果sql语句有条件限制的话，即执行 "select * from Sys_Department where ..."，则(一)中函数应改为：
public void DeptTree(TreeView tvMenu)
{
Dept_ds1 = myData.GetDept();//执行 "select * from Sys_Department"
Dept_ds2 = myData.GetDept(strWhere);//执行 "select * from Sys_Department where 
"
Dept_ds = Framework.Helper.TreeHelper.ResetParent(Dept_ds1, Dept_ds2, "DeptID", "DeptParent");//调整父节点
DeptTree(tvMenu, 0, (TreeNode)null);
}