The existing ICollectionView implementations in WPF, for example ListCollectionView, work very good in trivial cases, they even can sort and filter the items from the underlying collection, but they have some significant disadvantage: they do not keep the correct sort order of an item and they do not filter the item out if its property is changed until ICollectionView.Refresh() method is called explicitly.

To overcome this inconvenience I developed my own implementation of ICollectionView interface that listens to all its items property change events via WeakEventManager and fires corresponding collection change events to re-soft or re-filter the item if needed. It was not a very simple task for me, and I even debugged WPF source code a bit and realized that it works a bit strange, for example, ItemsControl cannot work with my ICollectionView implementation directly, instead it creates some CollectionViewProxy that wraps it and uses some proxy enumerator to access an item by index:

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When I worked on some navigation system I developed so called “Control Panel” with various custom WPF controls:

I created a simple white control with a black border derived from HwndHost (named LightGrid) and added it to ScrollViewer along with some other controls (replaced with “…”) as shown below:

<ScrollViewer HorizontalScrollBarVisibility="Disabled">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto" />
            ...
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            ...
        </Grid.RowDefinitions>
        ...
        <Border Grid.Row="6" Grid.ColumnSpan="2" Visibility="Visible" Height="200">
            <nc:LightGrid />
        </Border>
    </Grid>
</ScrollViewer>

It looks correctly in the lower scroll position, and it even can scroll inside ScrollViewer (it moves when I move the scroll bar), but when scrolled, it is not clipped so it obscures other controls:

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WPF implements UI Virtualization via VirtualizingStackPanel and it works great, but situation with Data Virtualization is a bit more complex.

After doing some experimentation I realized that VirtualizingStackPanel when used with WPF TreeView does not allow the data to be virtualized because it iterates through all the collection of data items from inside its MeasureOverride function. However, it access only visible data items when used with DataGrid or ListView, so it allows to use some paging or caching techniques in this case. See the following articles for more information:

• WPF: Data Virtualization – some simple example that uses paging technique.
• UI Virtualization vs. Data Virtualization (Part 1) – interesting sample that uses Dispatcher for deferred loading.

If you interested on what I tried to do with TreeView, please read below.

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