Checkboxes in ASP.NET TreeView

<%--
Related to Questions at:
a) http://groups.google.com/group/dotnetdevelopment/browse_thread/thread/99e294a7d64c4034/
b) http://groups.google.com/group/dotnetdevelopment/browse_thread/thread/6e502f3c0e182093
--%>

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
  <title>Untitled Page</title>
  <script type="text/javascript" language="javascript">
    function ToggleCheckBoxes(check)
    {
      var tvID = "<%= TreeView1.ClientID %>".concat("n0Nodes");
      var tvNodes = document.getElementById(tvID);
      var chkBoxes = tvNodes.getElementsByTagName("input");
      for (var i = 0; i < chkBoxes.length; i++)
      {
        var chk = chkBoxes[i];
        if (chk.type == "checkbox")
        {
          chk.checked = check;
        }
      }
    }
  </script>
</head>
<body>
  <form id="form1" runat="server">
    <asp:TreeView ID="TreeView1" ShowCheckBoxes="Leaf" runat="server">
      <Nodes>
        <asp:TreeNode Text="Parent1" Expanded="true">
          <asp:TreeNode Text="Child1" Checked="true">
            <asp:TreeNode Text="Child2" Checked="true" />
          </asp:TreeNode>
          <asp:TreeNode Text="Child3" />
          <asp:TreeNode Text="Child4" />
        </asp:TreeNode>
      </Nodes>
    </asp:TreeView>
    <a href="javascript:void(0)" onclick="ToggleCheckBoxes(true);">Check all</a>
    <br />
    <a href="javascript:void(0)" onclick="ToggleCheckBoxes(false);">Uncheck all</a>
  </form>
</body>
</html>