TreeView 生成最常見的一種編程實現方式就是通過“父子關係遞歸”生成樹，一般是自頂向下遞歸生成。這種方法的缺陷：“由父節點及子節點”的遍歷順序意味着每個子節點的父節點必須存在，否則將搜索不到，即出現“斷層現象”。
本文在遞歸原理的基礎上，通過調節父節點的層次，解決樹結構的斷層問題。
一、遞歸生成樹的算法：
#region 加載部門樹*****************************************************
DataSet Dept_ds;
/// <summary>
/// 加載部門樹
/// </summary>
public void DeptTree(TreeView tvMenu)
{
Dept_ds = myData.GetDept();//執行 "select * from Sys_Department"
DeptTree(tvMenu, 0, (TreeNode)null);
}
/// <summary>
/// 加載部門樹
/// </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]);
//過濾nodeParent,得到當前的所有子節點
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)
{ //添加根節點
newNode.SelectAction = TreeNodeSelectAction.SelectExpand;
newNode.Expanded = false;
newNode.PopulateOnDemand = false;
tvMenu.Nodes.Add(newNode);//***注意區別:根節點
DeptTree(null, Int32.Parse(drv[nodeId].ToString().Trim()), newNode);//遞歸
}
else
{ //?添加子節點
newNode.SelectAction = TreeNodeSelectAction.SelectExpand;
newNode.Expanded = false;
newNode.PopulateOnDemand = false;
pNode.ChildNodes.Add(newNode);//***注意區別:子節點
DeptTree(null, Int32.Parse(drv[nodeId].ToString().Trim()), newNode);//遞歸
}
}
}
#endregion
二、斷層處理原理：
遍歷篩選後的數據表newTable，獲取每個節點的所有父節點列表(從未經篩選的數據表oldTable中獲取)，判斷父節點是否完整存在於newTable中。通過依次調整父節點的層次，保證每個節點的最上級父節點最終爲根結點。
遞歸算法性能上是有點影響，對較少的數據處理還是可以的。下面給出具體實現類：
namespace Framework.Helper
{
/// <summary>
/// 樹形結構操作幫助類
/// </summary>
public static class TreeHelper
{
#region 重置數據表的父節點, 解決斷層問題
/// <summary>
/// 重置數據表的父節點, 解決樹形結構的斷層問題
/// </summary>
/// <param name="newTable">篩選後的數據表</param>
/// <param name="oldTable">未經篩選的數據表</param>
/// <param name="IDField">節點ID字段</param>
/// <param name="ParentField">父節點ID字段</param>
public static DataTable ResetParent(DataTable newTable, DataTable oldTable, string IDField, string ParentField)
{
//行循環篩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]);
//獲取指定節點在oldTable的所有父節點
string[] arrParent = GetAllParent(id, oldTable, IDField, ParentField).Split(',');
//遍歷oldTable中的所有父節點
for (int j = 0; j < arrParent.Length - 1; j++)
{
//判斷父節點是否在newTable中
if (HasNode(newTable, IDField, Convert.ToInt32(arrParent[j])))
{
//若在，設置爲父節點
newTable.Rows[i][ParentField] = Convert.ToInt32(arrParent[j]);
break;
}
else
{
//不在，設置父節點爲0
newTable.Rows[i][ParentField] = 0;
continue;
}
}
///通過這樣的調整，若節點node的父節點不再newTable中，就設置node.Parent = node.Parent.Parent,依次類推。
}
return newTable;
}
/// <summary>
/// 判斷指定ID的節點是否存在與指定數據表
/// </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 獲取指定節點的所有父節點
/// <summary>
/// 獲取指定節點的所有父節點ID
/// </summary>
/// <param name="ID">指定節點ID</param>
/// <param name="dataTable">數據表</param>
/// <param name="IDField">節點ID</param>
/// <param name="ParentField">父節點ID</param>
/// <returns>字符串,並以逗號隔開</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語句有條件限制的話，即執行 "select * from Sys_Department where ..."，則(一)中函數應改爲：
public void DeptTree(TreeView tvMenu)
{
Dept_ds1 = myData.GetDept();//執行 "select * from Sys_Department"
Dept_ds2 = myData.GetDept(strWhere);//執行 "select * from Sys_Department where "
Dept_ds = Framework.Helper.TreeHelper.ResetParent(Dept_ds1, Dept_ds2, "DeptID", "DeptParent");//調整父節點
DeptTree(tvMenu, 0, (TreeNode)null);
}