Expanding an ASP.Net TreeView node from code-behind - asp.net

Question

I'm learning how to access the controls of an ASP.Net master page and trying to expand a particular TreeView node. I'm doing this from another page that is not a master page.
objContentPlaceHolder, objLoginView and objTreeView all have a value as confirmed by using the debugger.
Can you look at this code and let us know why the code in the for loop is not executing? It reaches the for loop but just skips over the for loop at that point.
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim objContentPlaceHolder As ContentPlaceHolder
Dim objLoginView As LoginView
Dim objTreeView As TreeView
objContentPlaceHolder = CType(Master.FindControl("ContentPlaceHolderBody"), ContentPlaceHolder)
If Not objContentPlaceHolder Is Nothing Then
objLoginView = CType(objContentPlaceHolder.FindControl("loginViewMain"), LoginView)
If Not objLoginView Is Nothing Then
objTreeView = CType(objLoginView.FindControl("TreeViewMain"), TreeView)
' Make sure all nodes for Maintenance are expanded.
'--------------------------------------------------
For Each treenode As TreeNode In objTreeView.Nodes
If treenode.Text = "Maintenance" Then
treenode.Expand()
End If
Next treenode
End If
End If
End Sub
* Update *
I changed the page load event handler to a PreRenderComplete event handler and would you believe it worked? Not sure why PreRender didn't but that was it. Thanks again everyone for all the help.

Answer 1

public Sub TreeView_TreeNodeDataBound(ByVal sender As Object, ByVal e As TreeNodeEventArgs )
dim mapNode as SiteMapNode = e.Node.DataItem as SiteMapNode
If mapNode.Title = "Maintenance" then
e.Node.Expand()
End if
End Sub
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim objContentPlaceHolder As ContentPlaceHolder
Dim objLoginView As LoginView
Dim objTreeView As TreeView
objContentPlaceHolder = CType(Master.FindControl("ContentPlaceHolderBody"), ContentPlaceHolder)
If Not objContentPlaceHolder Is Nothing Then
objLoginView = CType(objContentPlaceHolder.FindControl("loginViewMain"), LoginView)
If Not objLoginView Is Nothing Then
objTreeView = CType(objLoginView.FindControl("TreeViewMain"), TreeView)
objTreeView.TreeNodeDataBound += TreeView_TreeNodeDataBound
End If
End If
End Sub
Hope this will help

Answer 2

From your example, it looks like your logic is only checking the root nodes. When dealing with hierarchical data, you need to employ recursive logic to ensure that the entire structure gets evaluated.
Something like this is what you need:
Protected Sub btnSearch_Click(sender As Object, e As EventArgs)
For Each node As TreeNode In TreeView1.Nodes
ExpandNodeByValue("Maintenance", node)
Next
End Sub
Private Sub ExpandNodeByValue(value As String, parentNode As TreeNode)
For Each childNode As TreeNode In parentNode.ChildNodes
If childNode.Value.ToLower() = value.ToLower() Then
childNode.Expand()
End If
If childNode.ChildNodes.Count > 0 Then
ExpandNodeByValue(value, childNode)
End If
Next
End Sub
I would also suggest using a DirectCast instead of CType, at least temporarily, to ensure that the control is being found. You would implement that like this:
Dim objTreeView as TreeView = DirectCast(objLoginView.FindControl("TreeViewMain"), TreeView)
If objTreeView IsNot Nothing Then
'The control was found
End If