38 lines
1.7 KiB
Markdown
38 lines
1.7 KiB
Markdown
## WPF TreeViewItem must be used within a TreeView
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### Scope
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Minor
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### Version Introduced
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4.5
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### Source Analyzer Status
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Available
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### Change Description
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A change was introduced in 4.5 that restricts usage of TreeViewItem elements outside of a TreeView. This manifests under the following conditions:
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- TreeViewItem's visual parent is not a panel. (A TreeViewItem generated for a TreeView will have a panel as its parent)
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- 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.
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- The VirtualizingStackPanel is item-scrolling (`ScrollUnit="Item"`).
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- 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.
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- The visual-parent chain from `v` to the VirtualizingStackPanel passes through the TreeViewItem.
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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
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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
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InvalidCastException that occurs within the WPF framework.
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- [ ] Quirked
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- [ ] Build-time break
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### Recommended Action
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A hotfix will be made available for this.
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### Affected APIs
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* Not detectable via API analysis
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### Category
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Windows Presentation Foundation (WPF)
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<!-- breaking change id: 141 -->
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