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 xref:System.Windows.Controls.TreeViewItem?displayProperty=name elements outside of a xref:System.Windows.Controls.TreeView?displayProperty=name. This manifests under the following conditions:

• xref:System.Windows.Controls.TreeViewItem?displayProperty=name's visual parent is not a panel. (A xref:System.Windows.Controls.TreeViewItem?displayProperty=name generated for a xref:System.Windows.Controls.TreeView?displayProperty=name will have a panel as its parent)
• The xref:System.Windows.Controls.TreeViewItem?displayProperty=name is a descendant of a xref:System.Windows.Controls.VirtualizingStackPanel?displayProperty=name acting as the "items host" for a list control (ListBox, DataGrid, ListView, etc.). Virtualization doesn't need to be enabled.
• The xref:System.Windows.Controls.VirtualizingStackPanel?displayProperty=name 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 xref:System.Windows.Controls.VirtualizingStackPanel?displayProperty=name passes through the xref:System.Windows.Controls.TreeViewItem?displayProperty=name.

In other words, this is seen when a xref:System.Windows.Controls.TreeViewItem?displayProperty=name is used outside of a xref:System.Windows.Controls.TreeView?displayProperty=name, and the user clicks on a descendant of the xref:System.Windows.Controls.TreeViewItem?displayProperty=name to bring it into view. If the xref:System.Windows.Controls.TreeViewItem?displayProperty=name has no focusable descendants, you'll never see this issue. An example of a situation where this is hit is when a xref:System.Windows.Controls.TreeViewItem?displayProperty=name 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)