generate html/asp dynamically - asp.net

Question

I have a treeview type structure of folders/links that's populated from a table. What I was attempting to do was procedural loop through my recordset and generate my html in page_init and then try and bind the controls. When I try to add the link buttons to the placeholders in html, it can never seem to find them.
I might be missing something fundamental here, all the examples i've seen bind a control thats already on the page, am I unable to generate the html myself in page_init?
example
Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Init
content_div.Innerhtml = "<asp:PlaceHolder id=""test"" runat=""server"" ></asp:PlaceHolder>"
End Sub
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
Dim _linkb As New LinkButton
_linkb.ID = "lb_cat_" & cat.uID
_linkb.Attributes.Add("href", "javascript: sltoggle('cat_" & cat.uID & "');")
_linkb.Attributes.Add("Text", "Expand/Close")
_linkb.Attributes.Add("runat", "server")
Dim ph As PlaceHolder = DirectCast(TRIEDEVERYTHINGUNDERTHESUN.FindControl("test"), PlaceHolder)
ph.Controls.Add(_linkb)
End Sub
If someone could point me in the right direction it'd be much appreciated
Regards,
Pete
UPDATE - full code
Private Sub load_dynamic_file_view()
Dim _sb As New StringBuilder
Dim _sfc As New sf_file_category, _sff As New sf_file
_lsfc = _sfc.get_all_sf_file_category
_lsff = _sff.get_active_sf_files
Dim _list_root As List(Of sf_file_category) = _lsfc.FindAll(Function(p) p.parent_id = 0)
If Not _list_root Is Nothing Then
_sb.Append("<strong>File Downloads</strong><br />")
_sb.Append("<div class=""indent-me"" ><br />")
For Each cat As sf_file_category In _list_root
'header/Open Link
Dim _linkb As New LinkButton
_linkb.ID = "lb_cat_" & cat.uID
_linkb.Attributes.Add("href", "javascript: sltoggle('cat_" & cat.uID & "');")
_linkb.Attributes.Add("Text", "Expand/Close")
_linkb.Attributes.Add("runat", "server")
Dim ph As PlaceHolder = DirectCast(Me.Master.FindControl("lb_cat_" & cat.uID), PlaceHolder)
ph.Controls.Add(_linkb)
_sb.Append(HtmlDecode(cat.name) & " <Asp:PlaceHolder id=""lb_cat_" & cat.uID & """ runat=""server"" /><br />")
'_sb.Append("<div id=""cat_" & cat.uID & """ class=""toggle-hide"">")
'_sb.Append(add_child_folder(cat.uID, content))
'_sb.Append(show_files(cat.uID, content))
'_sb.Append("</div><div class=""clearfix"" />")
Next
_sb.Append("</div>")
_sb.Append("<br /><br />")
End If
content_div.InnerHtml = _sb.ToString
End Sub
Private Function add_child_folder(ByVal catid As Long, ByRef content As ContentPlaceHolder) As String
Dim _sb As New StringBuilder
Dim _cl As List(Of sf_file_category) = _lsfc.FindAll(Function(p) p.parent_id = catid)
If Not _cl Is Nothing Then
_sb.Append("<div class=""indent-me"" ><br />")
'For Each _c As sf_file_category In _cl.OrderBy(Function(p) p.view_order)
_cl.Sort(Function(c1 As sf_file_category, c2 As sf_file_category)
Return c1.view_order.CompareTo(c2.view_order)
End Function)
For Each cat As sf_file_category In _cl
Dim _linkb As New LinkButton
_linkb.ID = "lb_cat_" & cat.uID
_linkb.Attributes.Add("href", "javascript: sltoggle('cat_" & cat.uID & "');")
_linkb.Attributes.Add("Text", "Expand/Close")
_linkb.Attributes.Add("runat", "server")
Content.Controls.Add(_linkb)
_sb.Append(HtmlDecode(cat.name) & " <Asp:LinkButton id=""lb_cat_" & cat.uID & """ runat=""server"" Text=""Expand/Close"" href='javascript: sltoggle('cat_" & cat.uID & "');' /><br />")
'_sb.Append("<div id=""cat_" & cat.uID & """ class=""toggle-hide"">")
_sb.Append(add_child_folder(cat.uID, content))
_sb.Append(show_files(cat.uID, content))
'_sb.Append("</div><div class=""clearfix"" >")
Next
_sb.Append("</div><br />")
End If
Return _sb.ToString
End Function
Private Function show_files(ByVal catid As Long, ByRef content As ContentPlaceHolder) As String
Dim _sb As New StringBuilder
Dim _fl As List(Of sf_file) = _lsff.FindAll(Function(p) p.file_category = catid)
If Not _fl Is Nothing Then
_sb.Append("<div class=""indent-me"" ><br />")
For Each _f As sf_file In _fl
Dim _linkb As New LinkButton
_linkb.ID = "file_" & _f.uID
_linkb.Attributes.Add("onCommand", "download_file")
_linkb.Attributes.Add("CommandArgument", _f.uID.ToString)
_linkb.Attributes.Add("Text", _f.file_name)
_linkb.Attributes.Add("runat", "server")
AddHandler _linkb.Command, AddressOf download_file
content.Controls.Add(_linkb)
_sb.Append("<asp:LinkButton id=""file_" & _f.uID & """ runat=""server"" onCommand=""download_file"" commandArgument=""" & _f.uID & """ Text=""" & _f.file_name & """ /><br />")
Next
_sb.Append("</div><br />")
End If
Return _sb.ToString
End Function

Answer 1

What your full code shows is that your building a massive string of HTML. This is fine for some smaller situations, but your code is clearly getting quite big now, and I would suggest you change this approach.
I would recommend that you declare web control equivalents, such as:
new HtmlGenericControl("div") instead of <div></div>
OR
new HtmlAnchor() OR new LinkButton() instead of <a></a>
In the example of a tree structure the HTML may look like this:
<ul>
<li>
ROOT
<ul>
<li>
LEVEL 1
</li>
</ul>
</li>
</ul>
To generate this in code you would do something similar to:
'Menu Holder
Dim treeStruct As HtmlGenericControl("ul")
'Root
Dim branch As HtmlGenericControl("li")
Dim branchItem as HtmlAnchor("a")
'Level 1
Dim subLevel As HtmlGenericControl("ul")
Dim subBranch As HtmlGenericControl("li")
Dim subBranchItem as HtmlAnchor("a")
'Setup Level 1
subBranchItem.InnerText = "LEVEL 1"
subBranchItem.Href = "levelone"
subBranch.Controls.Add(subBranchItem)
subLevel.Controls.Add(subBranch)
'Setup Root
branchItem.InnerText = "ROOT"
branchItem.Href = "root.htm"
'Add Link To Root
branch.Controls.Add(branchItem)
'Add Sub Branch To Root
branch.Controls.Add(subLevel)
treeStruct.Controls.Add(branch)
Important The code above is just for examples sake, ideally you would separate the functionality into functions for branch creation and then loop through your elements with your for loop.
You will also notice that I have used an <UL> instead of <DIV> as I would consider a tree structure to be an un-ordered list. Plus, you will also get the styling benefit from this more ridged structure.
I hope this helps

Answer 2

You generate only HTML tags and do not generate ASP.Net tags, as they can't be parsed by browser.
I think your code should be like
content_div.Innerhtml = "<div id='test'></div>"
ASP:Placeholder control is just a place holder and it is not equal to div HTML tag.
For an example i gave div tag here.

Answer 3

asp.net controls added as text are not known to the page and thus no viewstate / object is stored for it, thus you can never find it using Findcontrol.
Use the object of the control and add it to the parent control's Control collection
e.g.
div.Controls.Add(new PlaceHolder() { ... });
Once you have added it before Render event , its state will be saved and accessable.

Answer 4

It looks like your trying to add a placeholder to the content_div, however, what you are doing is rendering the tag as HTML content.
I don't know exactly what type of control content_div is, but can't you try:
content_div.controls.add(new placeholder() { ID = "test" });
This would then allow you to find the control within the content_div control.
However, what would probably be a much more concise solution for you might be the following:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
Dim _linkb As New LinkButton
_linkb.ID = "lb_cat_" & cat.uID
_linkb.Attributes.Add("href", "javascript: sltoggle('cat_" & cat.uID & "');")
_linkb.Attributes.Add("Text", "Expand/Close")
//you don't need this when using code behind
//_linkb.Attributes.Add("runat", "server")
//this will add your linkbutton to the content_div control
content_div.Controls.Add(_linkb)
End Sub
Give this ago and you should find it to be a useful way of dynamically building your page with asp controls.