黑马程序员之ASP.NET学习笔记:TREEVIEW中动态增加结点

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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() + " " +
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

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