We are getting following error: Is there any solution for this to fix

Object reference not set to an instance of an object.

   at Telerik.Windows.Controls.TreeView.TreeViewPanel.CleanupContainers(Int32 firstViewport, ItemsControl itemsControl)
   at Telerik.Windows.Controls.TreeView.TreeViewPanel.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.ContextLayoutManager.UpdateLayout()
   at System.Windows.ContextLayoutManager.UpdateLayoutCallback(Object arg)
   at System.Windows.Media.MediaContext.FireInvokeOnRenderCallbacks()
   at System.Windows.Media.MediaContext.RenderMessageHandlerCore(Object resizedCompositionTarget)
   at System.Windows.Media.MediaContext.RenderMessageHandler(Object resizedCompositionTarget)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)

Hello Ram Prasad,

This is the second time this error has been reported but unfortunately we have had no luck in reproducing in on our side.

Any help in reproducing this will really be appreciated.

Could you send us a sample project where the error is present? We are keen to look into this issue.

You can mail me directly at miroslav.paskov [at] telerik.com.

Kind regards,
Miroslav
the Telerik team

Hi,
I Have the same Problem. It is happening every time you close a branch in Hierarchical Mode
In my case I use a LoadOnDemand szenario, but that is not causing the problem.
I'ts an outOfBrowser Silverlight Application and i'm using the newest Silverlight libraries.

I wrote small test, If you want, I can send it to you.

Regards
Florian Gamper

Hello Florian,

This appears to be a bug in the RadTreeView caused by the HIerarchical  virtualization mode. I logged it in our PITS system where you will soon be able to view its status ( TreeView: HIerarchical Virtualization crashes the application when a TreeViewItem is collapsed). I updated your Telerik  points accordingly.
However, you can use the other two virtualization modes: "Standard" and "Recycling".

Thank you for your cooperation.

All the best,
Petar Mladenov
the Telerik team

Hi,

Unfortunately it's even not working in Recycling or Standard mode,
I think the "reclaiming" of unused objects only happens later.

I have a List of about 400 root nodes with approximately 4-8 Childrens each.
In Hierarchical it crashes every time,
In Recycling it's crashing at about the 15's closing,
In Standart it takes much longer, but it's happening nevertheless :(

Regards
Florian

Hello Florian,

Thank you for your efforts and involvement in the issue. We have some good news for you. We managed to fix this bug this afternoon and it will be included in the internal build that will be released tomorrow.

Thank you for your feedback again.

Sincerely yours,
Petar Mladenov
the Telerik team