[WASM] SettingsExpander does not render correctly

[MartinZikmund]

Current behavior

CommunityToolkit/Windows#393

Expected behavior

No response

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

No response

Workaround

No response

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

[ajpinedam]

We found the problem with this issue is connected to the Uno Expander Control.

The SettingsExpander has the following Style Configuration (simplified version):

<Expander>
    <Expander.Header>
        <SettingsCard />
    </Expander.Header>
    <Expander.Content>
        <ItemsControl />
    </Expander.Content>
</Expander>

When rendered, the SettingsCard is part of the Visual Tree, but the Data bound is not correct.

The SettingsCard sets a TemplateBinding from the Expander.Header but due to an issue on the TemplatedParent Syncronization this is returning the wrong information.

Expander Control Template Template (simplified version):

<!-- Expander ControlTemplate -->
<Grid>
    <RowDefinition x:Name="Row0" Height="Auto" />
    <RowDefinition x:Name="Row1" Height="*" />    
    <ToggleButton  Content="{TemplateBinding Header}" Style="{StaticResource ExpanderHeaderDownStyle}" />
    <Border>
        <ContentPresenter Content="{TemplateBinding Content}" Grid.Row="1" />
    </Border>
</Grid>


<!-- Expander Header Control Template (ExpanderHeaderDownStyle) -->
<Grid>
     <ContentPresenter x:Name="ContentPresenter" />
</Grid>

As can be seen, the Header ContentPresenter is inside a ToggleButton. When calling the TemplatedParentSyncronization here, this returns a level dip in the UI tree.

Specifically, in this line of code:

return (this.TemplatedParent as IFrameworkElement)?.TemplatedParent;

It's returning the Expander instead of the SettingsExpander

We believe that @Xiaoy312 PR 17645 will fix this issue since this PR is fixing issues related to the TemplatedParent like this one.