Treeview中ontreenodepopulate是一个很好的事件，当你点击树的某个节点时调入数据库展现此节点下的数据,并且无刷新，当树展现的数据多的时候就可以用此方法如MSDN的树，但如果数据不多的时候没有必要用此方法，因为要频繁调数据库
好闲话少说
由于是用户控件所以把 treeview的部分属性和事件公共，方便用此控件的页面调用
页面 TreeDept.ascx
<%@ Control Language="C#" AutoEventWireup="true" CodeFile="TreeDept.ascx.cs" Inherits="UserControls_TreeDept" %>
<asp:TreeView ID="TreeView1" runat="server" ExpandDepth="1" ImageSet="Contacts"
    NodeIndent="10" onselectednodechanged="TreeView1_SelectedNodeChanged"
    ontreenodepopulate="TreeView1_TreeNodePopulate" Width="101px">
    <ParentNodeStyle Font-Bold="True" ForeColor="#5555DD" />
    <HoverNodeStyle Font-Underline="False" />
    <SelectedNodeStyle Font-Underline="True" HorizontalPadding="0px"
        VerticalPadding="0px" />
    <NodeStyle Font-Names="Verdana" Font-Size="8pt" ForeColor="Black"
        HorizontalPadding="5px" NodeSpacing="0px" VerticalPadding="0px" />
</asp:TreeView>TreeDept.ascx.CS

public partial class UserControls_TreeDept : System.Web.UI.UserControl
{
  
    public event EventHandler DeptSel;
    public string DeptSelectNodeText
    {
        get { return TreeView1.SelectedNode.Text; }
    }
    SqlConnection con = new SqlConnection(@"server=LT-C9A4FDA64461;uid=sa;pwd=sa;database=ltweb");
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            BindTree();
        }
    }
    void BindTree()
    {
        TreeNode tn = new TreeNode();
        tn.Text = "软件";
        tn.Value = "1";
        tn.PopulateOnDemand = true;
        TreeView1.Nodes.Add(tn);

    }

    protected void TreeView1_TreeNodePopulate(object sender, TreeNodeEventArgs e)
    {
        SqlCommand cmd = new SqlCommand("select * from dept where parentID="+int.Parse(e.Node.Value),con);
        SqlDataAdapter sda = new SqlDataAdapter(cmd);
        DataTable dt = new DataTable();
        sda.Fill(dt);
        foreach (DataRow dr in dt.Rows)
        {
            TreeNode tn = new TreeNode(dr["Dept_Name"].ToString(), dr["Dept_ID"].ToString());
            tn.PopulateOnDemand = true;
            e.Node.ChildNodes.Add(tn);

        }
    }
    protected void TreeView1_SelectedNodeChanged(object sender, EventArgs e)
    {
        if(DeptSel!=null)
        DeptSel(this,EventArgs.Empty);
    }
}

public partial class Dept : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void DeptSel_Change(object sender, EventArgs e)
    {
        Response.Write(TreeDept1.DeptSelectNodeText);
    }
}