treeview 中出现的怪问题，求教高手解答，十万火急！！

[junzi6819]

在winCE下的应用程序，生成时没有任何错误，部署后出现如下错误：“treeview.exe nullReferenceException 位于 treeview.Form1.SetNodename()位于 treeview.Form1.ShowTree()位于 treeview.Form1_Load() 位于 System.windows.Forms.Form.OnLoad()位于 System.windows.Forms.Form._SetVisbl()位于 System.windows.Forms.Form.Set_Visbl()...

[haitangjv]

up up

[junzi6819]

我的代码：
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlServerCe;

namespace treeview
{
public partial class Form1 : Form
{
//private System.Data.SqlServerCe.SqlCeCommand sqlCeSelectCommand1;
//private System.Data.SqlServerCe.SqlCeCommand sqlCeInsertCommand1;
//private System.Data.SqlServerCe.SqlCeConnection sqlCeConnection1;
//private string cotegory_ID;
//private string cotegory_FatherID;
//private string cotegory_Name;
//private int cotegory_CengCi;
//private DataTable tblBom = new DataTable();
private Real_EstatePDADataSet.Building_CotegoryDataTable tblBom = new Real_EstatePDADataSet.Building_CotegoryDataTable();



public Form1()
{
InitializeComponent();
}

private void Form1_Load(object sender, EventArgs e)
{
this.ShowTree();//将Cotegory表用树形图的方式显示出来
}
//-------------读入数据并准备显示树形图-----------------
private void ShowTree()
{
tblBom.Clear();
this.building_CotegoryTableAdapter.Fill(tblBom);
DataView viewBom = new DataView(tblBom);//新建一个数据视图
viewBom.RowFilter = "层次码=0";

//将数据集中的所有记录逐个根据他们之间的关系添加到树形表中去
if (viewBom.Count > 0)
{
int i = 0;//由于低层码为0的产品可能不止一个，因此设置序号，以便准确定位父项
foreach (DataRowView myRow in viewBom)
{
string strName = SetNodeName(myRow["目录编号"].ToString().Trim());
//此处是添加前面头两个节点
this.treeView1.Nodes.Add(new TreeNode(strName));

//此处初始化参数是第一个节点,然后该函数会递归添加所有子节点
PopulateTreeView(strName, treeView1.Nodes[i], myRow);
i++;
treeView1.SelectedNode = treeView1.Nodes[0]; //选中第一个节点
}
}
}
//---------根据输入的节点信息，递归调用最终添加所有的节点-----------------------
private void PopulateTreeView(string parentPart, TreeNode parentNode, DataRowView parentRow)
{
string strName = "";
DataTable tempDataTable = tblBom.Copy();
DataView viewBom = new DataView(tempDataTable);

//筛选获得当前传递过来的节点的子项，并将其添加到树形图中
//判断方法是：凡父项编号等于传递过来的节点的目录名称的，就是该节点的子项
viewBom.RowFilter = "父目录编号 = '" + parentRow["目录编号"].ToString().Trim() + "'";
//递归的添加每一个节点的所有子节点
foreach (DataRowView myRow in viewBom)
{
string cotegoryID = myRow["目录编号"].ToString().Trim();
strName = SetNodeName(cotegoryID);
TreeNode myNode = new TreeNode(strName);
myNode.Tag = cotegoryID;
parentNode.Nodes.Add(myNode);
//函数递归调用，将所有节点按顺序添加完毕
PopulateTreeView(strName, myNode, myRow);
}
}
private string SetNodeName(string materialID)
{
string strConn = "Data Source = Real_EstatePDA.sdf;password = 'lnicynu'";
SqlCeConnection cn = new SqlCeConnection(strConn);
cn.Open();
try
{

SqlCeCommand cmd = cn.CreateCommand();
cmd.CommandText = "select 目录名称 from Building_Cotegory where 目录编号='" + materialID + "'";
string cotegoryName = cmd.ExecuteScalar().ToString().Trim();
cn.Close();
return (cotegoryName);
}
catch (SqlCeException e)
{

return (e.ToString());
//cn.Close();
}


}


private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
{

}


}
}