Binding behavior on Breadcrumbbar has changed in 5.6

[iurycarlos]

Current behavior

Fail to correct bind breadcrumb items in different scenarios.

Using a resourced ItemTemplate, breadcrumb will fail to accept pointer events.
Using a local Item content, breadcrumb will fail to construct its items.

App was working perfectly before updating to 5.6

Expected behavior

Breadcrumbbar should be working as expected, accepting click for " ... " when not enough space.

How to reproduce it (as minimally and precisely as possible)

A repro project can be found here:

BreadcrumbBindingBlank.zip

Workaround

Original issue was related to resourced ItemTemplate.
When trying to workaround using local content, we start to get the wrong rendering of items in the flyout.

Works on UWP/WinUI

None

Environment

No response

NuGet package version(s)

No response

Affected platforms

No response

IDE

No response

IDE version

No response

Relevant plugins

No response

Anything else we need to know?

No response

[MartinZikmund]

Based on my investigation so far it seems the problem is caused by TemplatedParent in some capacity. Specifically, BreadcrumbBarItem WinUI template uses the following for the individual buttons:

<Button x:Name="PART_ItemButton" x:DeferLoadStrategy="Lazy" ...>
	...
	<!-- This is the Button Content -->
	  <Grid AutomationProperties.AccessibilityView="Raw">
	  <ContentPresenter x:Name="PART_ItemContentPresenter"
	    AutomationProperties.AccessibilityView="Raw"
	    Content="{TemplateBinding Content}"
	    ContentTransitions="{TemplateBinding ContentTransitions}"
	    ContentTemplate="{TemplateBinding ContentTemplate}"
	    FontFamily="{TemplateBinding FontFamily}"
	    FontSize="{TemplateBinding FontSize}"
	    FontWeight="{TemplateBinding FontWeight}"
	    HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
	    VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
	    LineHeight="20" />
	  <TextBlock x:Name="PART_EllipsisTextBlock"
	    AutomationProperties.AccessibilityView="Raw"
	    FontFamily="{ThemeResource SymbolThemeFontFamily}"
	    FontSize="{TemplateBinding FontSize}"
	    Padding="3"
	    Text="&#xE712;"
	    Visibility="Collapsed"
	    VerticalAlignment="Stretch"
	    IsTextScaleFactorEnabled="False" />
	</Grid>
</Button>

Now, this worked before #15672, but after these changes the materialization presumably happens later, so during ElementStub.Materialize the Button gets created with no TemplatedParent initially and you can see that in the logs where you will see:

Applying template binding parent  on Microsoft.UI.Xaml.Controls.ContentPresenter

Note the two spaces after "parent" in the log - this is actually "null". As a result, the ContentPresenter.Content is left null and the buttons are invisible.

I am guessing the TemplatedParent of ContentPresenter needs to be evaluated correctly as BreadcrumbBarItem immediately when the ElementStub materialization happens, as TemplatedParent should remain "constant" throughout the lifecycle. However, I am not sure how to do that