51 lines
1.7 KiB
Markdown
51 lines
1.7 KiB
Markdown
## Item-scrolling a flat list with items of different pixel-height
|
|
|
|
### Scope
|
|
Minor
|
|
|
|
### Version Introduced
|
|
4.6.1
|
|
|
|
### Version Reverted
|
|
4.6.2
|
|
|
|
### Source Analyzer Status
|
|
Planned
|
|
|
|
### Change Description
|
|
When an ItemsControl displays a collection using virtualization (`IsVirtualizing=true`) and item-scrolling (`ScrollUnit=Item`),
|
|
and when the control scrolls to display an item whose height in pixels differs from its neighbors, the VirtualizingStackPanel
|
|
iterates over all items in the collection. The UI is unresponsive during this iteration; if the collection is
|
|
large, this can be perceived as a hang.
|
|
|
|
The iteration occurs in other circumstances, even in previous .Net releases. For example, it occurs when
|
|
pixel-scrolling (`ScrollUnit=Pixel`) upon encountering an item with different pixel height, and when item-scrolling
|
|
hierarchical data (such as a TreeView or an ItemsControl with grouping enabled) upon encountering an item with
|
|
a different number of descendant items than its neighbors.
|
|
|
|
For the case of item-scrolling and different pixel height, the iteration was introduced in .Net 4.6.1 to fix
|
|
bugs in the layout of hierarchical data. It is not needed if the data is flat (no hierarchy), and .Net 4.6.2
|
|
does not do it in that case.
|
|
|
|
- [ ] Quirked
|
|
- [ ] Build-time break
|
|
|
|
### Recommended Action
|
|
If the iteration occurs in .Net 4.6.1 but not in earlier releases - that is, if the ItemsControl is item-scrolling
|
|
a flat list with items of different pixel height - there are two remedies:
|
|
1. Install .Net 4.6.2.
|
|
2. Install hotfix HR 1605 for .Net 4.6.1.
|
|
|
|
### Affected APIs
|
|
* `T:System.Windows.Controls.VirtualizingStackPanel`
|
|
|
|
### Category
|
|
Windows Presentation Foundation (WPF)
|
|
|
|
<!--
|
|
### Original Bug
|
|
202599
|
|
-->
|
|
|
|
<!-- breaking change id: 152 -->
|