When you reorder the collection very fast an exception is thrown. This is reproducible when the UI virtualization is enabled with its virtualization mode set to Recycling, and an item is selected. Also, you can observe some missing items glitches instead of the exception. To reproduce this you can call the ObservableCollection's Move() method several times in a single method (see the attached project). 

In this case also a NullReferenceException is thrown sometimes instead of the InvalidOperationException.

To work this around delay the reordering calls so that the treeview has time to properly measure and arrange itself. For example:

Items.Move(10, 2);
Application.Current.Dispatcher.BeginInvoke(new Action(() =>
{
Items.Move(10, 2);
}), System.Windows.Threading.DispatcherPriority.Background);

The built-in drag drop mechanism works with the containers of the items and makes a snapshot of them for the DragVisual. Thus, dragging multiple selected items that are not present in the viewport is not possible.

with RadTreeView control,using MVVM binding,the xaml like :
AutoScrollToSelectedItem="True"  IsVirtualizing="False"
looking the attach files,Navigate by the  RadBreadcrumb(the RadBreadcrumb and the RadTreeView binding the same data source,and binding the same SelectedIem),
when expand the level4,the RadTreeView  can't bring the selected item to view,but scroll mouse to the seleced item view,then Navigate again the same postion ,it can scroll,the radtreeview can reach the selected item.
     I test the microsoft treeview,if the Virtualizing is true,it can't scroll the selected item,but set the Virtualizing  to false,it is good.
    the other question,how to set the style?the  selected item's highligh area can expand the full row,like the visual studio.

When expanding all items with a horizontal scrollbar the last item is hidden by the scrollbar. As a workaround, you can set the IsVirtualizing property of the RadTreeView to True.

This behavior is reproducible when we have applied Material theme and we have disabled the selection and drag of a RadTreeViewItem. 
A possible workaround is to set the MaterialAssist.CheckedBrush attached property to Null of the RadTreeViewItem which you don't want to select and drag.

 xmlns:material="clr-namespace:Telerik.Windows.Controls.MaterialControls;assembly=Telerik.Windows.Controls"

 <telerik:RadTreeViewItem Header="RootItem" material:MaterialAssist.CheckedBrush="{x:Null}" />

When sorting a table I get the following stacktrace.

06.12.2016 15:39:34 Error General Object reference not set to an instance of an object.
System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Windows.Controls.ItemContainerGenerator.Remove(GeneratorPosition position, Int32 count, Boolean isRecycling)
   at Telerik.Windows.Controls.TreeView.TreeViewPanel.CleanupRange(IList children, IItemContainerGenerator generator, Int32 startIndex, Int32 count)
   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 MS.Internal.Helper.MeasureElementWithSingleChild(UIElement element, Size constraint)
   at System.Windows.Controls.ItemsPresenter.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
   at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV, Boolean& hasDesiredSizeUChanged)
   at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Control.MeasureOverride(Size constraint)
   at Telerik.Windows.Controls.RadTreeViewItem.MeasureOverride(Size availableSize)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at Telerik.Windows.Controls.TreeView.TreeViewPanel.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at MS.Internal.Helper.MeasureElementWithSingleChild(UIElement element, Size constraint)
   at System.Windows.Controls.ItemsPresenter.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
   at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV, Boolean& hasDesiredSizeUChanged)
...

Setting the HeaderStringFormat of RadTreeViewItem does not format the Header.

As a workaround, HeaderTemplate of RadTreeViewItem could be set which has TextBlock with StringFormat property set on its Text Binding.



 <DataTemplate x:Key="template">
                <TextBlock Text="{Binding ., StringFormat='Received ({0:N0})'}" />
</DataTemplate>


Available in LIB version: 2016.3.1121

Generated item cache is not cleared properly. This leads to memory leaking when items are virtualized and realized. 

As a workaround you can set the IsVisualCacheEnabled property of the TreeViewPanel to False. Note that this will work only in Recycling VirtualizationMode.

<telerik:RadTreeView.ItemsPanel>
    <ItemsPanelTemplate>
        <telerik:TreeViewPanel IsVisualCacheEnabled="False" />
    </ItemsPanelTemplate>
</telerik:RadTreeView.ItemsPanel>

The vertical scroll cannot be moved via the mouse wheel or by clicking on the scrollbar's thumb after the End key is pressed. This is reproducible ONLY if the UI virtualization is enabled and if there are many items (500-1000+).

When this property is set to false the changes are not saved.

Edit:
We have reviewed this item and we can confirm this is by design and it is not bug. IsInEditMode serves only for opening / closing the edit mode of the RadTreeViewItem. 
The way to submit changes is to use CommitEdit() method.

Virtualized RadTreeView.

Windows Display Size is set to Larger (150%).

Expanding and collapsing TreeViewItems leads to ArgumentException in TreeViewPanel.ExtendDesiredSize method - "Width and Height must be non negative".

Available in LIB version: 2015.3.1207 

A common request is to have a way to hide the root node of a RadTreeView so that the second-level nodes are displayed without a root.  If the RadTreeView is bound, it appears that this can be done through the hierarchical binding if one know what one is doing.  However, there does not seem to be a simple way to do it if the nodes to be added to the RadTreeView are added programmatically.  It would be helpful if there were a binary property on the RadTeeView to set whether the root node is displayed.


Reason for decline:
Both in databound tree or not , you can add only the items you need to display in the root source / root items collection of the tree. Generally, there is no value of hiding a root node that has children - why is inside the collection at all ?

Currently, in Extended SelectionMode,  RadTreeView selects multiple Items with Shift + Click selection only if there is another RadTreeViewItem already selected with mouse.

Other controls like RadListBox, RadGridView hold reference to the business object which should be the start (the target) of the multiselection. RadTreeView holds such reference with weak reference to the container (RadTreeViewItem) and only if this container is selected with Mouse.

Adding such method (SetSelectionAnchor) in RadTreeView will help users better control the multiselection process.

If the  RadTreeView control is used on touch device in scenario with Checkbox support, the TreeViewItem  cannot be (un)checked with a single tap.  

Available in LIB version: 2015.3.1109

If you define a RadMaskedInput control in the ItemEditTemplate of RadTreeView and then bind the Value property of the masked input to a property from the RadTreeViewItem's view model, the input displays the view model's class ToString() method. Instead the value of the bound property should be displayed.

Fix is available in LIB Version: 2015.3.1005.

RadTreeViewItem is focused but it is not selected.

KeyDown should select the item below the focused one but it does not.


Will be available in Q3 2015 Release.

RadTreeView with virtualization turned on, defines HierarchicalDataTemplates for its items. 

In the template, the root panel is 32 pixels (or higher than the default TreeViewItemHeight - 24 px in OfficeBlackTheme). Scrolling the treeview, then maximizing the wpf window results in misplaced / incorrect height of treeviewitems.

Possible workaround:
Set the MinHeight property of RadTreeViewItem so that all its header content fits. Then set the item's VerticalContentAlignment to Stretch
        <Style TargetType="telerik:RadTreeViewItem">
                         <Setter Property="MinHeight" Value="48" />
                        <Setter Property="VerticalContentAlignment" Value="Stretch" />
                   </Style>

Also following settings might help:
   - setting fixed width/height of the RadTreeView
   - setting ChildDefaultLength to 48 of every TreeviewPanel:
			<telerik:RadTreeView.ItemsPanel>
				<ItemsPanelTemplate>
					<telerik:TreeViewPanel ChildDefaultLength="48" />
				</ItemsPanelTemplate>
			</telerik:RadTreeView.ItemsPanel>
        <Style x:Key="ItemContainerStyle" TargetType="{x:Type telerik:RadTreeViewItem}">
			<Setter Property="ItemsPanel">
				<Setter.Value>
					<ItemsPanelTemplate>
						<telerik:TreeViewPanel ChildDefaultLength="48" />
					</ItemsPanelTemplate>
				</Setter.Value>
			</Setter>

TreeView is bound to CollectionViewSource. Certain items are expanded. The CVS is refreshed leading to ArgumentOutOfRange Exception in the TreeViewPanel.cs

NOTE: The bug is reported via the following scenario. When the bound IsExpanded property is changed in the model, OnCollectionChanged with NotifyChangedCollectionAction.Reset is invoked.

We consider this as highly unsafe operation. What actually happens is that by the time containers are measured / arranged (because the IsExpanded is triggered) - Reset also triggers reset / measure arrange of all items. This is the same as modifying a list/collection when it is iterated - the framework wll throw an error.

To better prove this is unsafe, we also tested System.Windows.Controls.TreeView. On MouseDown, we set IsExpanded = true on collased item and in the PropertyChnaged handler we invoked OnCollectionChanged with Reset in the bound ObservableCollection. This resulted in StackOverflowException in PresentationCore.dll.

Conclusions. The Exception is fixed in the RadTreeView but we consider invoking Reset in such moment (during measure/arrange) as not supported / critical / unsafe operation.

In scenarios when both ScrollViewers (vertical and horizontal are visible), pressing Home Key might lead to freezing of the Vertical ScrollBar.

Available in LIB version: 2015.1.0309

Expose properties that controls the lines color and their thickness like in the RadTreeListView.