Referencing an item in a VirtualizingStackPanel

Question

I'm playing with the "Grid Application," which is a C++ Metro app template provided by VS11. The main display is a collection of items displayed in a VirtualizingStackPanel:

<ScrollViewer x:name="itemGridScrollViewer">
  <GridView x:name="itemGridView">
    <GridView.ItemsPanel>
      <ItemsPanelTemplate>
        <VirtualizingStackPanel />
      </ItemsPanelTemplate> 
    </GridView.ItemsPanel>
  </GridView>
</ScrollViewer>

The actual items are displayed using the Standard250x250ItemTemplate data template defined in StandardStyles.xaml. One of the display elements of this is a graphic.

I'm trying to understand how to reference a specific item so that I can change the graphic at runtime. The ScrollViewer and the GridView have objects associated with them, so I can get to those, but I don't see how to get from there to the individual items.

All this stuff is completely new to me, so be gentle. :)

score 0 · Answer 1 · answered Mar 09 '12 at 18:33

In general it's not a good idea to dig down into individual templated items in an ItemsControl because not only is it a pain, but that ItemTemplate can regenerate at different times (paging during virtualization, source collection updates, etc) and you'll be left holding an outdated UIElement that's no longer being displayed.

A better approach is to pull the data you need into the item data and in the ItemTemplate use Data Binding to make whatever changes you need to differentiate the UI. One option is to use an IValueConverter to get a different image depending on some state in the item data:

<GridView>
  <GridView.ItemTemplate>
    <DataTemplate>
      <Image Source="{Binding Path=DataState, Converter={StaticResource MyStateToImageConverter}}"/>
    </DataTemplate>
  </GridView.ItemTemplate>
</GridView>

Here I'm assuming that the converter code has been written and an instance of the converter has already been declared as a resource (see here). You could alternatively do a direct Binding to a property on each item's data that specifies its image and skip the converter part.

Referencing an item in a VirtualizingStackPanel

1 Answers1