Random programming things I'd want to remember

Friday, July 20, 2012

Windows Phone 7 ItemsControl within an ItemsControl, solving slow loading issue

So it happened that I needed to show a long list within a long list. I found that the scrolling performance of a ListBox was not up to par, so I tried an ItemsControl. Here is the XAML:

    MaxWidth="450" VirtualizingStackPanel.VirtualizationMode="Recycling"
    ItemsSource="{Binding AnswersForDisplayAsAListBySomeNumberOfElements}"
    Visibility="{Binding ThisOneHasALongAnswer, Converter={StaticResource showLongAnswer}}">
            <VirtualizingStackPanel />
            <ScrollViewer x:Name="InnerScrollViewer" Padding="{TemplateBinding Padding}" MaxHeight="400">
                <ItemsPresenter />
            <TextBlock Text="{Binding}" TextWrapping="Wrap" />

Upon binding, if the ItemsList is visible, it displays a scrollable list. The problem with this approach is that once the inner list is scrolled to the bottom (or to the top), the outer ItemsList is not being scrolled. After playing with it for a bit, I figured out that if the ScrollViewer is removed from the ItemsControl.Template part of the control declaration, then the long list is displayed in its entire height and scrolling the individual item scrolls the entire outer ItemsList

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