Get Element Root's ViewModel Context in WINUI3 - xaml

Question

I have a page which contains a ListView x:bound to an object in my ViewModel. This object contains a list of objects (timestamps) that contains a list of Subjects that contains a list of another objects. I'm presenting the data in 2 list views, one inside another.
<ListView
x:Name="primaryList" // for exemplification purposes
ItemsSource="{x:Bind ViewModel.VideoProject.TimeStamps, Mode=OneWay}"
ItemClick='{x:Bind ViewModel.ListViewTimeStamps_ItemClick, Mode=OneWay}'>
The ListView contains a DataTemplate for another ListView
<ListView.ItemTemplate>
<DataTemplate>
<StackPanel Spacing="5">
<TextBlock Text="{Binding Id}"
FontSize="15"
HorizontalAlignment="Left"
FontWeight="Bold" />
<ListView ItemsSource="{Binding Subjects}"
x:Name="secondaryList"
SelectionMode="Multiple">
<ListView.ItemTemplate>
....
And the second ListView is followed by another same structure.
My goal is to bind the second ListView ItemClickEvent to ListViewTimeStamps_ItemClick method inside my ViewModel, because I need the data contained in the object that secondaryListView holds (Subject).
I could try to set the Data Template Context to the ViewModel but it would break the Subject bind.
I found a ton of questions about this topic but differently from WPF there's not AncestorType to catch the up tree reference.
Obs:
My project is based on the Template Model which creates the XAML .cs with the ViewModel as a Property. I also haven't set the DataContext on the XAML page because I can x:bind normally my view model to the page elements without explicit set.
Is there a way to accomplish without using Attached Properties?
Thank you.

Answer 1

Since there is no support for setting the AncestorType property of a RelativeSource in WinUI, there is no way to accomplish this in pure XAML without writing some code.
You could implement an attached bevaiour as suggested and exemplified here:
public static class AncestorSource
{
public static readonly DependencyProperty AncestorTypeProperty =
DependencyProperty.RegisterAttached(
"AncestorType",
typeof(Type),
typeof(AncestorSource),
new PropertyMetadata(default(Type), OnAncestorTypeChanged)
);
public static void SetAncestorType(FrameworkElement element, Type value) =>
element.SetValue(AncestorTypeProperty, value);
public static Type GetAncestorType(FrameworkElement element) =>
(Type)element.GetValue(AncestorTypeProperty);
private static void OnAncestorTypeChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
FrameworkElement target = (FrameworkElement)d;
if (target.IsLoaded)
SetDataContext(target);
else
target.Loaded += OnTargetLoaded;
}
private static void OnTargetLoaded(object sender, RoutedEventArgs e)
{
FrameworkElement target = (FrameworkElement)sender;
target.Loaded -= OnTargetLoaded;
SetDataContext(target);
}
private static void SetDataContext(FrameworkElement target)
{
Type ancestorType = GetAncestorType(target);
if (ancestorType != null)
target.DataContext = FindParent(target, ancestorType);
}
private static object FindParent(DependencyObject dependencyObject, Type ancestorType)
{
DependencyObject parent = VisualTreeHelper.GetParent(dependencyObject);
if (parent == null)
return null;
if (ancestorType.IsAssignableFrom(parent.GetType()))
return parent;
return FindParent(parent, ancestorType);
}
}
So no replacement so far for AncestorType?
No. Not in XAML.