ASP.NET treeview populate child nodes. How can I avoid a postback to server?
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Published on 2010-04-14T04:36:31Z
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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); } }
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