Hi all,

this topic is driving me nuts. ;)

With this article: http://aspalliance.com/732 I was able to get my treeview built on demand. If I expand a node, the server retrieves the necessary data froman SQL database (in my case) and then populates the treeview without the need of a postback. Client Callback makes this possible. ;)

Every new node gets a checkbox. Since ASP.NET 2.0 does not add an autopostback to the treeview, the state of the checkboxes can only be seen by the server after a postback triggered somehow else. This does not matter, since I have a Button on my page that finally triggers a postback.

With this article: http://www.webswapp.com/codesamples/viewsource.aspx?file=~/codesamples/aspnet20/treeview/treenodecheckchanged.aspx I would expect, that when this postback is triggered, all checkbox events get noticed by the server and I can gather them.

The Problem now is, that the TreeNodeCheckChanged event seems to be only triggered by the client, when the checkbox was already there when the treeview has been initially rendered. This means that if I populate a node on demand and programmatically add a checkbox, this checkbox doesn't fire a TreeNodeCheckChanged event...

Is there any way to get this properly working?

Of course I can call a serverside ExpandAll and CollapseAll. This would populate the whole treeview at once and then it would work. But this does not make sense, since I would loose all advantages of using the OnDemand feature... :-(

I hope anyone has an answer to this.

Best regards and thanks
for reading this,

Christian.

Hi,

thanks for reading my article. :-)

I'm not sure if I understand what you mean. If you let it populate the nodes, add CheckBox to them, and check a dynamically added node (it's CheckBox) and then cause the postback finally, it throws the TreeNodeCheckChanged event, at least in my test scenario (same code as in the article just changed

Private Sub PopulateNodes(ByVal dt As DataTable, ByVal nodes As TreeNodeCollection)

For Each dr As DataRow In dt.Rows

Dim tn As New TreeNode()

tn.Text = dr("title").ToString()

tn.Value = dr("id").ToString()

tn.ShowCheckBox = True

nodes.Add(tn)

'If node has child nodes, then enable on-demand populating

tn.PopulateOnDemand = (CInt(dr("childnodecount")) > 0)

Next

End Sub

Or have I misunderstood something? If yes, then please clarify

No you got it all right. The effect I have is, that if I don't submit the fully expanded tree to the client when the page is initially opened, checked events for dynamically populated subnodes do not get fired.

It's like that:

+ O Root Node

I Open "Root Node" and the node is populated on demand to:

- O Root Node
  + O Sub Node

If I check "Sub Node" and hit a postback button, the buttons' event handler is called, but not the TreeNodeCheckChanged event.

Now, if I declare my treeview with the ExpandDepth attribute set to 1, so that the client shows

- O Root Node
  + O Sub Node

immediately, I can check "Sub Node" and on postback, the corresponding TreeNodeCheckChanged event is fired. This is really weird...

Regards,
Christian.

Just a quick note to everyone:

I was able to solve this problem. Some demo code has been published here: http://www.webswapp.com/codesamples/viewsource.aspx?file=~/codesamples/aspnet20/treeview/populateondemand.aspx to demonstrate the populateondemand feature.

With the help of this code I found out, that the code-behind rebuilds the tree on postback to be able to handle the corresponding events. This makes sense. Without tree, no events. I had a mistake in my code. Actually, the database connection to the data source was not available on postback, so the tree couldn't be rebuilt and therefor, the check events couldn't be handled.

I reinitiated the database connection on postback and voila, it worked.

Thanks for your help guys and
best regards,

Christian.