Inconsistent behavior of Behaviors SDK - xaml

Question

I have the following, very simple repro case. It's a Universal Windows (Phone) 8.1 app. I have a very simple model:
public class SimpleModel
{
public bool IsLoading { get; set; } = false;
}
and a collection of these models, defined as shared classes:
public class SimpleModelCollection : List<SimpleModel>
{
public SimpleModelCollection()
{
this.Add(new SimpleModel());
this.Add(new SimpleModel());
this.Add(new SimpleModel());
this.Add(new SimpleModel());
this.Add(new SimpleModel());
this.Add(new SimpleModel());
}
}
I have only a single page in both Windows and Windows Phone 8.1 project. They have identical XAML, a simple ItemsControl:
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<ItemsControl x:Name="items" HorizontalAlignment="Center">
<ItemsControl.ItemTemplate>
<DataTemplate>
<Grid>
<interactivity:Interaction.Behaviors>
<core:DataTriggerBehavior Binding="{Binding IsLoading}" Value="True">
<core:ChangePropertyAction TargetObject="{Binding ElementName=text}" PropertyName="Visibility" Value="Visible"/>
</core:DataTriggerBehavior>
<core:DataTriggerBehavior Binding="{Binding IsLoading}" Value="False">
<core:ChangePropertyAction TargetObject="{Binding ElementName=text}" PropertyName="Visibility" Value="Collapsed"/>
</core:DataTriggerBehavior>
</interactivity:Interaction.Behaviors>
<StackPanel>
<TextBlock x:Name="text" Text="Should I be visible?" FontSize="26"></TextBlock>
</StackPanel>
</Grid>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</Grid>
Of course, Behaviors SDK is added to both (Win & WP 8.1) projects.
In code-behind, I set the ItemsSource to an instance of the previously mentioned simple model collection. Windows Phone constructor:
public MainPage()
{
this.InitializeComponent();
this.items.ItemsSource = new SimpleModelCollection();
this.NavigationCacheMode = NavigationCacheMode.Required;
}
and Windows constructor:
public MainPage()
{
this.InitializeComponent();
this.items.ItemsSource = new SimpleModelCollection();
}
What would you expect as a result if IsLoading was initialized to false:
public bool IsLoading { get; set; } = false;
Let me show you what the app looks like if Isloading is initialized to false on Windows Phone:
This is OK, and completely expected, since the Visibility maps to the bool value, so the TextBlocks should be collapsed if IsLoading is false. But on Windows, they are not:
My question is - why? What am I missing?
This is also problematic when comparing WP 8.1 behavior with the behavior in Windows 10 UWP. In UWP it behaves just like on Windows 8.1, which make porting from WP 8.1 to UWP a bit painful.
EDIT: The full repro project is here: https://github.com/igrali/BehaviorsSDK_Bug

Answer 1

This is indeed a bug. I can see two ways to fix it.
First, if you absolutely know that the initial state of the TextBlocks should be Collapsed, you can default them to Collapsed in XAML as it only doesn't work for the first time.
Alternatively, you can attach all the Behaviors to the Textblock directly inside the template. This should work too.
<DataTemplate>
<Grid>
<StackPanel>
<TextBlock x:Name="text" Text="Should I be visible?" FontSize="26">
<interactivity:Interaction.Behaviors>
<core:DataTriggerBehavior Binding="{Binding IsLoading}" Value="True">
<core:ChangePropertyAction TargetObject="{Binding ElementName=text}" PropertyName="Visibility" Value="Visible" />
</core:DataTriggerBehavior>
<core:DataTriggerBehavior Binding="{Binding IsLoading}" Value="False">
<core:ChangePropertyAction TargetObject="{Binding ElementName=text}" PropertyName="Visibility" Value="Collapsed" />
</core:DataTriggerBehavior>
</interactivity:Interaction.Behaviors>
</TextBlock>
<Button Click="Button_Click" Content="Visible?" />
</StackPanel>
</Grid>
</DataTemplate>