ASP.NET treeview populate child nodes. How can I avoid a postback to server?
- by mas_oz2k1
I am trying to test populate on demand for a treeview.
I follow the procedure from these links:
http://msdn.microsoft.com/en-us/library/e8z5184w.aspx
But the treeview still make a postback to the server if I expanded one of the tree nodes (If you put a breakpoint in the first line of Page_load event), thus refreshing the whole page. I am using VS2005 and Asp.net 2.0 (but the same issue occurs in VS2008)
My simple test page markup is:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="aspTreeview.aspx.cs" Inherits="aspTreeview" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<table>
<tr>
<td style="height: 80%; width: 45%;">
<asp:Panel ID="Panel1" runat="server" BorderColor="#0033CC" BorderStyle="Solid" ScrollBars="Both">
<asp:TreeView ID="TreeView1" runat="server" ShowLines="True" PopulateNodesFromClient="True" EnableClientScript="True" NodeWrap="True"
ontreenodepopulate="TreeView1_TreeNodePopulate" ExpandDepth="0">
</asp:TreeView>
</asp:Panel>
</td>
<td style="width: 10%; height: 80%;" >
<div>
<asp:Button ID="Button1" runat="server" Text="->" onclick="Button1_Click" />
</div>
<div>
<asp:Button ID="Button2" runat="server" Text="<-" />
</div>
</td>
<td style="width: 136px; height: 80%">
<asp:Panel ID="Panel2" runat="server" BorderColor="Lime" BorderStyle="Solid">
<asp:TreeView ID="TreeView2" runat="server" ShowLines="True" ExpandDepth="0">
</asp:TreeView>
</asp:Panel>
</td>
</tr>
<tr>
<td>
</td>
<td>
</td>
<td style="width: 136px">
</td>
</tr>
</table>
</div>
</form>
</body>
</html>
The code behind is:
protected void Page_Load(object sender, EventArgs e)
{
Debug.WriteLine("Page_Load started.");
if (!IsPostBack)
{
if (Request.Browser.SupportsCallback)
Debug.WriteLine("Browser supports callback scripts.");
for (int i = 0; i < 3; i++)
{
TreeNode node = new TreeNode("ENTRY " + i.ToString());
node.Value = i.ToString();
node.PopulateOnDemand = true;
node.Expanded = false;
TreeView1.Nodes.Add(node);
}
}
Debug.WriteLine("Page_Load finished.");
}
protected void TreeView1_TreeNodePopulate(object sender, TreeNodeEventArgs e)
{
TreeNode targetNode = e.Node;
for (int j = 0; j < 4200; j++)
{
TreeNode subnode = new TreeNode(String.Format("Sub ENTRY {0} {1}", targetNode.Value, j));
subnode.PopulateOnDemand = true;
subnode.Expanded = false;
targetNode.ChildNodes.Add(subnode);
}
}
