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POWhat is the proper method of grouping a Collection in Windows Store App (Metro) using LINQ and VB.NET?
 

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  1. POWhat is the proper method of grouping a Collection in Windows Store App (Metro) using LINQ and VB.NET?
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    <p>I'm a fairly novice programmer, and making a Windows Store App. I have an object that contains an <code>ObservableCollection(Of T)</code> that I want to group for display in a <code>ListView</code>. Using LINQ to return a set of grouped items seems like it would be the best and easiest choice. Every piece of documentation I could find says that Group By returns <code>IEnumerable(Of IGrouping(Of TKey, TItem))</code> and you set <code>CollectionViewSource.IsSourceGrouped</code> to True, bind to the CVS and it should all work perfectly. Right?</p> <p>Not so much.</p> <p>I have a class that contains</p> <pre><code>Public Property Items As ObservableCollection(Of Item) Public ReadOnly Property GroupedItems As IEnumerable Get ' Return grouped items End Get End Property </code></pre> <p>And in the XAML for the page, where <code>GroupedItems</code> is set as the <code>Page</code>'s <code>DataContext</code> in code-behind:</p> <pre><code>&lt;Page.Resources&gt; &lt;CollectionViewSource x:Name="GroupedItems" Source="{Binding}" IsSourceGrouped="True" /&gt; &lt;/Page.Resources&gt; &lt;Grid Background="{StaticResource ApplicationPageBackgroundThemeBrush}"&gt; &lt;ListView ItemsSource="{Binding Source={StaticResource GroupedItems}}"&gt; &lt;ListView.GroupStyle&gt; &lt;GroupStyle.HeaderTemplate&gt; &lt;DataTemplate&gt; &lt;!-- Template --&gt; &lt;/DataTemplate&gt; &lt;/GroupStyle.HeaderTemplate&gt; &lt;/ListView.GroupStyle&gt; &lt;ListView.ItemTemplate&gt; &lt;DataTemplate&gt; &lt;!-- Template --&gt; &lt;/DataTemplate&gt; &lt;/ListView.ItemTemplate&gt; &lt;/ListView&gt; &lt;/Grid&gt; </code></pre> <p>Now, if I bind the <code>ListView</code> to the <code>ObservableCollection(Of Item)</code> directly, the <code>ListView</code> renders all the items as expected, following the <code>ItemTemplate</code>. But when it is bound to the supposedly-grouped <code>CollectionViewSource</code>, the <code>ListView</code> renders the groups according to the <code>HeaderTemplate</code>, but it doesn't render any of the items within the group.</p> <p>I've inspected the results of the LINQ logic:</p> <pre><code>Dim x = From i As Item In Items Group i By Key = i.SubItem Into Group </code></pre> <p>And <code>x</code> has a <code>Key</code> property and a <code>Group</code> property, though it is some kind of IEnumerable(Of anonymous) type rather than an <code>IEnumerable(Of IGrouping(Of TKey, TItem))</code>.</p> <p>So what am I doing wrong here? Is there another caveat to the VB.NET implementation of LINQ that I'm missing? Is there a property I'm forgetting to set? What is the right way to do this?</p>
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