dotnet/Documentation/compatibility/wpf-treeviewitem-must-be-used-within-a-treeview.md

WPF TreeViewItem must be used within a TreeView

Scope

Minor

Version Introduced

4.5

Source Analyzer Status

Available

Change Description

A change was introduced in 4.5 that restricts usage of TreeViewItem elements outside of a TreeView. This manifests under the following conditions:

• TreeViewItem's visual parent is not a panel. (A TreeViewItem generated for a TreeView will have a panel as its parent)
• The TreeViewItem is a descendant of a VirtualizingStackPanel acting as the "items host" for a list control (ListBox, DataGrid, ListView, etc.). Virtualization doesn't need to be enabled.
• The VirtualizingStackPanel is item-scrolling (ScrollUnit="Item").
• Someone calls VirtualizingStackPanel.MakeVisible(v) to scroll an element v into view. This can be done explicitly, or implicitly in a number of ways; perhaps the most common way is simply clicking on v to give it the keyboard focus.
• The visual-parent chain from v to the VirtualizingStackPanel passes through the TreeViewItem.

In other words, this is seen when a TreeViewItem is used outside of a TreeView, and the user clicks on a descendant of the TreeViewItem to bring it into view. If the TreeViewItem has no focusable descendants, you'll never see this issue. An example of a situation where this is hit is when a TreeViewItem is the root of a DataTemplate. When this issue is hit, there is an InvalidCastException that occurs within the WPF framework.

• Quirked
• Build-time break

Recommended Action

A hotfix will be made available for this.

Affected APIs

• Not detectable via API analysis

Category

Windows Presentation Foundation (WPF)