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I have a virtualized TreeView with these properties:

<TreeView
    ScrollViewer.CanContentScroll="True" 
    VirtualizingPanel.IsVirtualizing="True"
    VirtualizingPanel.IsVirtualizingWhenGrouping="True" 
    VirtualizingStackPanel.ScrollUnit="Pixel"  
    VirtualizingStackPanel.CacheLength="20,20"
    VirtualizingStackPanel.CacheLengthUnit="Item"
    />
  ...
</TreeView>

The TreeViewItem's are roughly the same height.

The problem is that when scrolling down the handle of the scrollbar changes size and the scrolling is "jumpy" which leads to a quite poor user experience.

How might one obtain a more smooth UX?

Bent Rasmussen
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  • So far my conclusion is that TreeView is almost impossible to make performant. So I'll simulate the treeview behaviour with a listview/box. Too bad. – Bent Rasmussen Feb 15 '13 at 21:08

2 Answers2

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I realize that this is an old post and you probably have a solution now, but it has a simple answer, so for anyone who may come across this in the future, here it is:

The behaviour you describe is normal. Had you search in MSDN for ScrollViewer.CanContentScroll which is the very first property that you used, you would have found this:

Content in a ScrollViewer can be scrolled in terms of physical units or logical units. Physical units are device independent pixels. Logical units are used for scrolling items within an ItemsControl. The default behavior of the ScrollViewer is to use physical units to scroll its content. However, in cases where the CanContentScroll is set to true, the content could use logical units to scroll. For example, ListBox, ListView, and other controls that inherit from ItemsControl use logical units to scroll. If CanContentScroll is true, the values of the ExtentHeight, ScrollableHeight, ViewportHeight, and VerticalOffset properties are number of items, instead of physical units.

If you require physical scrolling instead of logical scrolling, wrap the host Panel element in a ScrollViewer and set its CanContentScroll property to false. Physical scrolling is the default scroll behavior for most Panel elements.

So, this basically means that you can either scroll in terms of pixels, or whole items from the collection. Therefore, to have smooth scrolling, you'll want to scroll using pixels. To do that, you simply need to set the ScrollViewer.CanContentScroll property to False. So it turns out that it is an easy fix after all.

Community
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Sheridan
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  • I seem to remember also doing that - tweaking all these settings to see if we could get both performance and smooth scrolling. However it's a while ago now, so I honestly don't remember anymore. We switched to using a ListView and simulating the tree behavior, which is of course somewhat sad. I'll follow-up on this to make sure we didn't miss that however... – Bent Rasmussen Jan 13 '14 at 21:44
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Unfortunately, setting ScrollViewer.CanContentScroll = False will disable virtualization so doesn't really help with this problem.

I have found that setting a hard coded height value to the content of your TreeViewItem makes the scrollbar behave a lot better, but the scroll bar still resizes a bit.

Michael
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