おそらく手遅れですが、この問題に遭遇する可能性のある他の人にこの答えを残しておきます。CollectionViewSourceはビジュアル/論理ツリーに属していないため、CollectionViewSource.Sourceのバインディングは機能せず、データコンテキストを継承せず、バインディングのソースとしてComboBoxを参照することもできません。次のクラスを使用して、これを醜い、しかし簡単な方法で解決することができました。
/// <summary>
/// Provides a way to set binding between a control
/// and an object which is not part of the visual tree.
/// </summary>
/// <remarks>
/// A bright example when you need this class is having an
/// <see cref="ItemsControl"/> bound to a <see cref="CollectionViewSource"/>.
/// The tricky thing arises when you want the <see cref="CollectionViewSource.Source"/>
/// to be bound to some property of the <see cref="ItemsControl"/>
/// (e.g. to its data context, and to the view model). Since
/// <see cref="CollectionViewSource"/> doesn't belong to the visual/logical tree,
/// its not able to reference the <see cref="ItemsControl"/>. To stay in markup,
/// you do the following:
/// 1) Add an instance of the <see cref="BindingBridge"/> to the resources
/// of some parent element;
/// 2) On the <see cref="ItemsControl"/> set the <see cref="BindingBridge.BridgeInstance"/> attached property to the
/// instance created on step 1) using <see cref="StaticResourceExtension"/>;
/// 3) Set the <see cref="CollectionViewSource.Source"/> to a binding which has
/// source set (via <see cref="StaticResourceExtension"/>) to <see cref="BindingBridge"/>
/// and path set to the <see cref="BindingBridge.SourceElement"/> (which will be the control
/// on which you set the attached property on step 2) plus the property of interest
/// (e.g. <see cref="FrameworkElement.DataContext"/>):
/// <code>
/// <CollectionViewSource
/// Source="{Binding SourceElement.DataContext.Images, Source={StaticResource ImagesBindingBridge}}"/>
/// </code>.
///
/// So the result is that when assigning the attached property on a control, the assigned
/// <see cref="BindingBridge"/> stores the reference to the control. And that reference can be
/// retrieved from the <see cref="BindingBridge.SourceElement"/>.
/// </remarks>
public sealed class BindingBridge : DependencyObject
{
#region BridgeInstance property
public static BindingBridge GetBridgeInstance(DependencyObject obj)
{
Contract.Requires(obj != null);
return (BindingBridge)obj.GetValue(BridgeInstanceProperty);
}
public static void SetBridgeInstance(DependencyObject obj, BindingBridge value)
{
Contract.Requires(obj != null);
obj.SetValue(BridgeInstanceProperty, value);
}
// Using a DependencyProperty as the backing store for BridgeInstance. This enables animation, styling, binding, etc...
public static readonly DependencyProperty BridgeInstanceProperty =
DependencyProperty.RegisterAttached("BridgeInstance", typeof(BindingBridge), typeof(BindingBridge),
new PropertyMetadata(OnBridgeInstancePropertyChanged));
#endregion BridgeInstance property
#region SourceElement property
public FrameworkElement SourceElement
{
get { return (FrameworkElement)GetValue(SourceElementProperty); }
private set { SetValue(SourceElementPropertyKey, value); }
}
// Using a DependencyProperty as the backing store for SourceElement. This enables animation, styling, binding, etc...
private static readonly DependencyPropertyKey SourceElementPropertyKey =
DependencyProperty.RegisterReadOnly("SourceElement", typeof(FrameworkElement), typeof(BindingBridge), new PropertyMetadata(null));
public static readonly DependencyProperty SourceElementProperty;
#endregion SourceElement property
/// <summary>
/// Initializes the <see cref="BindingBridge"/> class.
/// </summary>
static BindingBridge()
{
SourceElementProperty = SourceElementPropertyKey.DependencyProperty;
}
private static void OnBridgeInstancePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var sourceElement = (FrameworkElement)d;
var bridge = (BindingBridge)e.NewValue;
bridge.SourceElement = sourceElement;
}
}
使用例を次に示します（リソース辞書は表示されていません）。
<ItemsControl
infrastructure:BindingBridge.BridgeInstance="{StaticResource ImagesBindingBridge}">
<ItemsControl.ItemsSource>
<Binding>
<Binding.Source>
<CollectionViewSource
Source="{Binding SourceElement.DataContext.Images, Source={StaticResource ImagesBindingBridge}, Mode=OneWay}">
<CollectionViewSource.SortDescriptions>
<componentModel:SortDescription PropertyName="Timestamp" Direction="Descending"/>
</CollectionViewSource.SortDescriptions>
</CollectionViewSource>
</Binding.Source>
</Binding>
</ItemsControl.ItemsSource>
</ItemsControl>