本文介绍如何使用ASP.NET 2.0动态地从数据库加载树形结构的数据，并展示了一个具体的实例，即从SQL Server 2000的PUBS数据库中获取作者及其作品信息。
在asp.net 2.0中，要动态从数据库中取出内容，动态增加结点，其实不难，比如以SQL SERVER 2000的PUBS数据库为例子，要以树型列表方式，取出作者，做为根结点，然后取出每位作者写过什么书，作为子结点，可以这样
<%@ Page Language="C#"%>
<%@ Import Namespace="System.Data"%>
<%@ Import Namespace="System.Data.SqlClient"%>
<%@ Import Namespace="System.Configuration"%>
<!DOCTYPE htmlPUBLIC"-//W3C//DTD XHTML 1.1//EN""http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Dynamic Population of the TreeView Control</title>
<script runat=server>
void Node_Populate(object sender,
System.Web.UI.WebControls.TreeNodeEventArgs e)
{
if(e.Node.ChildNodes.Count == 0)
{
switch( e.Node.Depth )
{
case 0:
FillAuthors(e.Node);
break;
case 1:
FillTitlesForAuthors(e.Node);
break;
}
}
}
void FillAuthors(TreeNode node)
{
string connString = System.Configuration.ConfigurationSettings.
ConnectionStrings["NorthwindConnnection"].ConnectionString;
SqlConnection connection = new SqlConnection(connString);
SqlCommand command = new SqlCommand("Select * From
authors",connection);
SqlDataAdapter adapter = new SqlDataAdapter(command);
DataSet authors = new DataSet();
adapter.Fill(authors);
if (authors.Tables.Count > 0)
{
foreach (DataRow row in authors.Tables[0].Rows)
{
TreeNode newNode = new
TreeNode(row["au_fname"].ToString() + " " +
row["au_lname"].ToString(),
row["au_id"].ToString());
newNode.PopulateOnDemand = true;
newNode.SelectAction = TreeNodeSelectAction.Expand;
node.ChildNodes.Add(newNode);
}
}
}
void FillTitlesForAuthors(TreeNode node)
{
string authorID = node.Value;
string connString = System.Configuration.ConfigurationSettings.
ConnectionStrings["NorthwindConnnection"].ConnectionString;
SqlConnection connection = new SqlConnection(connString);
SqlCommand command = new SqlCommand("Select T.title,
T.title_id From titles T" +
" Inner Join titleauthor TA on
T.title_id = TA.title_id " +
" Where TA.au_id = '" + authorID + "'", connection);
SqlDataAdapter adapter = new SqlDataAdapter(command);
DataSet titlesForAuthors = new DataSet();
adapter.Fill(titlesForAuthors);
if (titlesForAuthors.Tables.Count > 0)
{
foreach (DataRow row in titlesForAuthors.Tables[0].Rows)
{
TreeNode newNode = new TreeNode(
row["title"].ToString(), row["title_id"].ToString());
newNode.PopulateOnDemand = false;
newNode.SelectAction = TreeNodeSelectAction.None;
node.ChildNodes.Add(newNode);
}
}
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:TreeViewRunat="Server" ExpandImageUrl="Images/closed.gif"
CollapseImageUrl="Images/open.gif"
OnTreeNodePopulate="Node_Populate" ID="tvwauthors">
<Nodes>
<asp:TreeNodeText="Authors" PopulateOnDemand=true
Value="0"/>
</Nodes>
</asp:TreeView>
</div>
</form>
</body>
</html>
其中，注意ontreenodepopulate事件，是在展开树的结点时发生的，这里定义了自定义的NODE_POPULATE,在node_populate中，检查当前结点的深度，如果是0，就是根结点，于是就调用FillAuthors过程，取出所有的作者，如果深度是1，则是叶子结点，调用FillTitlesForAuthors过程。其中，要注意它们中的动态建立树结点的过程，如：
TreeNode newNode = new TreeNode(row["au_fname"].ToString() + " " +
<%@ Page Language="C#"%>
<%@ Import Namespace="System.Data"%><%@ Import Namespace="System.Data.SqlClient"%><%@ Import Namespace="System.Configuration"%><!DOCTYPE htmlPUBLIC"-//W3C//DTD XHTML 1.1//EN""http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head runat="server"> <title>Dynamic Population of the TreeView Control</title> <script runat=server> void Node_Populate(object sender, System.Web.UI.WebControls.TreeNodeEventArgs e) { if(e.Node.ChildNodes.Count == 0) { switch( e.Node.Depth ) { case 0: FillAuthors(e.Node); break; case 1: FillTitlesForAuthors(e.Node); break; } } } void FillAuthors(TreeNode node) { string connString = System.Configuration.ConfigurationSettings.ConnectionStrings["NorthwindConnnection"].ConnectionString; SqlConnection connection = new SqlConnection(connString); SqlCommand command = new SqlCommand("Select * From authors",connection); SqlDataAdapter adapter = new SqlDataAdapter(command); DataSet authors = new DataSet(); adapter.Fill(authors); if (authors.Tables.Count > 0) {
foreach (DataRow row in authors.Tables[0].Rows) { TreeNode newNode = new TreeNode(row["au_fname"].ToString() + " " + row["au_lname"].ToString(), row["au_id"].ToString()); newNode.PopulateOnDemand = true; newNode.SelectAction = TreeNodeSelectAction.Expand; node.ChildNodes.Add(newNode); } } } void FillTitlesForAuthors(TreeNode node) { string authorID = node.Value; string connString = System.Configuration.ConfigurationSettings.ConnectionStrings["NorthwindConnnection"].ConnectionString; SqlConnection connection = new SqlConnection(connString); SqlCommand command = new SqlCommand("Select T.title, T.title_id From titles T" +" Inner Join titleauthor TA on T.title_id = TA.title_id " + " Where TA.au_id = '" + authorID + "'", connection); SqlDataAdapter adapter = new SqlDataAdapter(command); DataSet titlesForAuthors = new DataSet(); adapter.Fill(titlesForAuthors); if (titlesForAuthors.Tables.Count > 0) { foreach (DataRow row in titlesForAuthors.Tables[0].Rows) { TreeNode newNode = new TreeNode(row["title"].ToString(), row["title_id"].ToString()); newNode.PopulateOnDemand = false; newNode.SelectAction = TreeNodeSelectAction.None; node.ChildNodes.Add(newNode); } } } </script></head><body> <form id="form1" runat="server"> <div> <asp:TreeViewRunat="Server" ExpandImageUrl="Images/closed.gif" CollapseImageUrl="Images/open.gif" OnTreeNodePopulate="Node_Populate" ID="tvwauthors"> <Nodes> <asp:TreeNodeText="Authors" PopulateOnDemand=trueValue="0"/> </Nodes> </asp:TreeView> </div> </form></body></html>其中，注意ontreenodepopulate事件，是在展开树的结点时发生的，这里定义了自定义的NODE_POPULATE,在node_populate中，检查当前结点的深度，如果是0，就是根结点，于是就调用FillAuthors过程，取出所有的作者，如果深度是1，则是叶子结点，调用FillTitlesForAuthors过程。其中，要注意它们中的动态建立树结点的过程，如：
TreeNode newNode = new TreeNode(row["au_fname"].ToString() + " " +
row["au_lname"].ToString(),
row["au_id"].ToString());
newNode.PopulateOnDemand = true;
newNode.SelectAction = TreeNodeSelectAction.Expand;
node.ChildNodes.Add(newNode);
其中， popluateondemand属性表明，该结点会动态扩展。
其中， popluateondemand属性表明，该结点会动态扩展。
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