Here is the problem: I have an XML bound Treeview control which displays product categories and sub-categories.
When a sub-category is clicked, a new page is opened displaying products. Now I want this subcategory to stay expanded.

First I had to remove NavigateUrlField from the TreeNodeBinding since OnSelectedNodeChanged is not beeing fired in that case.
I solved the problem by storing the URL in the ValueField property.

Anyway, here is the Treeview definition:
<asp:TreeView ID="TreeView2" runat="server" DataSourceID="XmlDataSource1" ImageSet="Custom" NodeIndent="10" ExpandDepth=1 OnSelectedNodeChanged=store_node>

Here is the Sub being fired:

Sub store_node(ByVal sender As Object, ByVal e As System.EventArgs)
        Session("node") = TreeView2.SelectedNode.ValuePath  ' store the ValuePath in Session
        If Len(TreeView2.SelectedValue.ToString) > 5 Then Response.Redirect(TreeView2.SelectedValue)   ' redirect to the product page if these is a link
End Sub

After that, Session("node") looks something like this:
Kategorije/Informatika/procesori/katalog.aspx?grupa=110050&main=313&gn=PROCESORI&pgn=AMD%20AM2

Here is the code I use to select that node:

If Not Session("node") Is Nothing Then
            If Session("node").ToString <> "" Then
                Dim selNode As TreeNode = TreeView2.FindNode(Session("node").ToString)
                selNode.Select()
            End If
End If
Session("node") = ""

But it's not wokring, I get the following error:

"System.NullReferenceException: Object reference not set to an instance of an object" in the line selNode.Select()

 
Any help would be appriciated.
 

 Be Sure to check for object instance before trying to assign a value.

i.e.

If not isNothing(selNode) then

selNode.Select() 

end if 

PS when do you call this method on page load or some other event. 

I tried it but nothing happens, there is no error now but the code between if...end if is not beeing executed at all.

If Not IsNothing(selNode) Then
    selNode.Select()
    Response.Write(selNode.Text)
End If

The method is called on page load. 

Hi,

In your treeview you set ExpandDepth  is 1, you could change the treeview ExpandDepth property, set its value is FullyExpand.

 I tried it but it doesn't help, no node is beeing selected

Hi,

If  you want to make the node be selected, please do not use selNode.Select(), try to use selNode.Selected = true;

Tried it, but nothing.

Dim selNode As TreeNode = TreeView2.FindNode(Session("node").ToString) 'I think the problem lies here, no node is found so the if...end if block after that is not executed at all
If Not IsNothing(selNode) Then
     selNode.Selected = True
     Response.Write(selNode.Text)
End If

 

Hi,

 The value of the node's ValuePath is the path fron the root node to the current node, it should be like this "Home/Administration/Sub 1", I do not understand

why your Session("node")( Session("node") = TreeView2.SelectedNode.ValuePath ) like this:

Kategorije/Informatika/procesori/katalog.aspx?grupa=110050&main=313&gn=PROCESORI&pgn=AMD%20AM2

I defined ValueField="URL", and obviously this value field is also passed to the ValuePath.

I did this because this is the only way (that I know) to pass the URL value. If I use NavigateUrlField then OnSelectedNodeChanged is not fired.
 

U just tried removing ValueField="URL" from the TreeNodeBinding, so the ValuePath looks like this now:

Kategorije/Informatika/procesori/amd am2
 

But it still doesn't work, so I guess the URL in ValuePath doesn't make a difference.

I am keeping tracking this question from the very begining. and I have been trying it following Amanda's sugguestion, and it all worked. Therefore, may I ask you what your fanal question is? if the following code didn't execute or there was no node be selected?

If Not IsNothing(selNode) Then
    selNode.Select()
    Response.Write(selNode.Text)
End If

Hi,

I think we are on the wrong way to solve your original problem. the problem is that you want to the sub-category to open a subpage in a new page, and keep the sub-category staying expanded. Right?

If it is right, you could only set the  ExpandDepth =FullyExpand, do not need to implement it by codebehind.

The findnode method's parameters valuepath that is the value path of a node(from the root node to current node),  but your Session("node").ToString is not a path of the node, but is an url, when you use the findnode method to get the node ( TreeView2.FindNode(Session("node").ToString) ) from treeview control at the specified value path, it will show error.

If these could not help you, would you please provide the xml file for futher help!

>Hi,
> I think we are on the wrong way to solve your original problem. the problem is that you want to the sub-category to open a subpage in a new page, and keep the sub-category staying expanded. Right?

Yes, exactly

>If it is right, you could only set the  ExpandDepth =FullyExpand, do not need to implement it by codebehind.

But then all the subcategories will be expanded all the time, and I don't wan't that, since there will be many of them

>The findnode method's parameters valuepath that is the value path of a node(from the root node to current node),  but your Session("node").ToString is not a path of the node, but is an url, when you use >the findnode method to get the node ( TreeView2.FindNode(Session("node").ToString) ) from treeview control at the specified value path, it will show error.

I also tried it without the link, so the Session("node") would only contain the path but it still didn't work
>If these could not help you, would you please provide the xml file for futher help!

Here is my XML:

<?xml version="1.0" ?>

<Kategorije>

  <MenuItem1 Title="Auto akustika">
    <MenuItem3 Title="Dodatna oprema" URL="katalog.aspx?grupa=760090&amp;main=1&amp;gn=Auto%20akustika&amp;pgn=Dodatna%20oprema"/>
    <MenuItem3 Title="Kablovi" URL="katalog.aspx?grupa=760070&amp;main=1&amp;gn=Auto%20akustika&amp;pgn=Kablovi"/>
  </MenuItem1>
 
  <MenuItem1 Title="Informatika">
    <MenuItem2 Title="ra?unala">
      <MenuItem3 Title="pc racunala" URL="katalog.aspx?grupa=100010&amp;main=315&amp;gn=RACUNALA&amp;pgn=PC%20ra?unala"/>
    </MenuItem2>
    <MenuItem2 Title="procesori">
      <MenuItem3 Title="amd am2" URL="katalog.aspx?grupa=110050&amp;main=313&amp;gn=PROCESORI&amp;pgn=AMD%20AM2"/>
      <MenuItem3 Title="intel celeron" URL="katalog.aspx?grupa=110010&amp;main=313&amp;gn=PROCESORI&amp;pgn=Intel%20Celeron"/>
    </MenuItem2>
  </MenuItem1>

</Kategorije>

>>I also tried it without the link, so the Session("node") would only contain the path but it still didn't work.

Could you please discribe more clearly how it didn't work? what do you want it to do? and could you please tell me whether you still bind the Valud filed to "URL"? Is it the code between If...end not executed? if so did you debug it what the Session("node")'s value was? Thank you!

at the moment I am not binding the Value field to URL, the code between if..end if is still not executed, since no node is still beeing found.

the value of Session("node") is for ex. "Kategorije/Informatika/procesori/intel celeron"

here is the latest version of the TreeView (all the code bellow is placed in a file "menu.ascx" which is called from all the pages):

<asp:TreeView ID="TreeView2" runat="server" DataSourceID="XmlDataSource1" ImageSet="Custom" NodeIndent="10" ExpandDepth=1 OnSelectedNodeChanged=sel_node>
            <LevelStyles>
                <asp:TreeNodeStyle ChildNodesPadding=2 cssclass="izdvojeni" Font-Underline="true" />
                <asp:TreeNodeStyle NodeSpacing=4 cssclass="tab1" Font-Underline="true"/>
                <asp:TreeNodeStyle cssclass="tab2" Font-Underline="true" />
                <asp:TreeNodeStyle cssclass="tab3" Font-UnderLine="True" />
            </LevelStyles>
            <DataBindings>
                <asp:TreeNodeBinding DataMember="MenuItem1" TextField="Title" SelectAction="Expand" />
                <asp:TreeNodeBinding DataMember="MenuItem2" TextField="Title" SelectAction="Expand" />
                <asp:TreeNodeBinding DataMember="MenuItem3" TextField="Title" SelectAction="Select" />
            </DataBindings>
</asp:TreeView>

Here is the sel_node sub:

Sub sel_node(ByVal sender As Object, ByVal e As System.EventArgs)
        Session("node") = TreeView2.SelectedNode.ValuePath
        Response.Redirect("about.aspx") 'this is a test page which also contains menu.ascx  where the selected node should be expanded
End Sub

And finally here is Page_Load of the menu.ascx:

Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
        If Not Session("node") Is Nothing Then
            Response.Write(Session("node"))
            If Session("node").ToString <> "" Then
                Dim selNode As TreeNode = TreeView2.FindNode(Session("node"))
                If Not IsNothing(selNode) Then
                    selNode.Selected = True
                    Response.Write(selNode.Text)
                    selNode.Expand()
                End If
            End If
        End If
        Session("node") = ""
    End Sub
 

Could it maybe be that there is no node found because the treeview is still not populated at the moment?

I got it to work, partially at least. It seems the problem was that the treeview was not populate on pageload when I tried to find the node, so now I did the following:

<asp:TreeView ID="TreeView2" runat="server" DataSourceID="XmlDataSource1" ImageSet="Custom" NodeIndent="10" ExpandDepth=1 OnSelectedNodeChanged=sel_node OnDataBound=treeview_bound> 

Removed all the code from page_load, and made a new sub:

Sub treeview_bound(ByVal sender As Object, ByVal e As System.EventArgs)
        If Not Session("node") Is Nothing Then
            If Session("node").ToString <> "" Then
                Dim selNode As TreeNode = TreeView2.FindNode(Server.HtmlDecode(Session("node")))
                If Not IsNothing(selNode) Then
                    selNode.Selected = True
                    Try
                        TreeView2.CollapseAll()
                        Dim nodeToExpand As TreeNode = selNode
                        While Not (nodeToExpand Is Nothing)
                            nodeToExpand.Expanded = True
                            nodeToExpand = nodeToExpand.Parent
                        End While
                    Catch ex As Exception
                    End Try
                End If
            End If
        End If
    End Sub

So this works now.

But when I try using NavigateUrlField="URL", funny thing happens: the sel_node sub is not executed any more !?

Any ideas why?

Or is there maybe some other way I could use the URL from XML?
 

Everything works now

My bad in the last post, I got so confused with all this that I tried using NavigateUrlField="URL" instead of ValueField="URL".

So now I added ValueField="URL", and everything works fine, a new page is opened with the link I passed, and the selected node is expanded.

Thank you all for your feedback.