XAML Binding only works on first item of array? - wpf

Question

I have a custom user control which has a dependency property as follows:
public static readonly DependencyProperty PagesProperty =
DependencyProperty.Register("Pages", typeof(IEnumerable<MyContentPage>), typeof(UC_ApplicationWindow),
new PropertyMetadata(new List<MyContentPage>()));
public IList<MyContentPage> Pages
{
get => (IList<MyContentPage>)GetValue(PagesProperty);
set => SetValue(PagesProperty, value);
}
I use this in another project something like this:
<graphicElements:UC_ApplicationWindow>
<graphicElements:UC_ApplicationWindow.Pages>
<x:Array Type="{x:Type graphicElements:MyContentPage}">
<graphicElements:MyContentPage>
<graphicElements:MyContentPage.Content>
<StackPanel>
<ContentControl DataContext="{Binding DataContext, ElementName=gd_Main}">
...some content
</ContentControl>
...other content
</StackPanel>
</graphicElements:MyContentPage.Content>
</graphicElements:MyContentPage>
<graphicElements:MyContentPage>
<graphicElements:MyContentPage.Content>
<StackPanel>
<ContentControl DataContext="{Binding DataContext, ElementName=gd_Main}">
...some content
</ContentControl>
...other content
</StackPanel>
</graphicElements:MyContentPage.Content>
</graphicElements:MyContentPage>
</x:Array>
</graphicElements:UC_ApplicationWindow.Pages>
</graphicElements:UC_ApplicationWindow>
Basically in one part of the content I'm trying to pull the DataContext from the context of the parent grid (gd_Main) instead of the page that is passed down to it. My ElementName binding works... for the first element in the array. For all other elements in the array I get this:
Cannot find source for binding with reference 'ElementName=gd_Main'. BindingExpression:Path=DataContext; DataItem=null; target element is 'ContentControl' (Name=''); target property is 'DataContext' (type 'Object')
What am I missing? Why would it bind properly for the first item and not for the rest? Is there a better way to go about this?

Answer 1

Ok I'm not sure if this is the best solution but I got it to work. What I ended up doing was basically going brute force and manually setting the datacontext. I created the value in the constructor as an observable collection and subscribed to the collection changed event like this:
Pages = new ObservableCollection<MyContentPage>();
((ObservableCollection<MyContentPage>)Pages).CollectionChanged += UC_ApplicationWindow_CollectionChanged;
Then in the collection changed event I bind the data context of the individual items to the data context of the current control. Here is that method:
void UC_ApplicationWindow_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
foreach (MyContentPage pg in e.NewItems.OfType<MyContentPage>())
{
var bnd = new Binding(nameof(DataContext)) {Source = this};
pg.Content.SetBinding(FrameworkElement.DataContextProperty, bnd);
}
}
Note that I couldn't just directly set the DataContext because on initialization while it's parsing out the XAML the data context is not yet set, plus it may change later, so I needed to create an actual binding so it updates properly.
Also worth noting. This is essentially doing the same thing as the comment by #Shivani Katukota above with one difference which is fairly crucial in my case but may be inconsequential in others. This method binds in code behind as items are added to the collection, binding in XAML means that you have to do it in the XAML for each item. My control is designed to have other users use it in other projects so having to set it in XAML would require me to give the user that instruction and it wouldn't work right if they didn't do so. If you are doing this internally it's not a really big deal to just use {x:Reference}...