UWP Why does a style not apply to TargetTypes in DataTemplate?

Question

Given a style in a Page.Resource:

    <Style x:Name="ItemTitle" TargetType="TextBlock">
        <Setter Property="FontSize" Value="16"></Setter>
        <Setter Property="FontWeight" Value="Bold"></Setter>
    </Style>

It is correctly applied to any regular TextBlock on the same page.

However, when I use a DataTemplate for an Item in a GridView on that page, this style does not apply.

    <DataTemplate  x:Key="Output" x:DataType="vm:Output">
        <TextBlock Text="{x:Bind Text}"></TextBlock>
    </DataTemplate>

It does work when I apply the style explicitly on the DataTemplate, e.g.:

    <DataTemplate  x:Key="Output" x:DataType="vm:Output">
        <TextBlock Style="{StaticResource ItemTitle}" Text="{x:Bind Text}"></TextBlock>
    </DataTemplate>

Does anyone know what's up?

Answer 1

It's expected and intentional. If it doesn't derive from Control (like DataTemplate) then it won't inherit an implicit style unless they're in the application resource dictionaries as global defaults.

Or more specifically;

Templates are viewed as an encapsulation boundary when looking up an implicit style for an element which is not a subtype of Control.

Hope this helps. Cheers.

Addendum:

If it's a situation where you have a lot of the same element nested in a Template you can just set it once and allow it to inherit to all the nested controls of the type like (in pseudo);

<Parent>
  <Parent.Resources>
    <Style TargetType="TextBlock" BasedOn="{StaticResource ItemTitle}"/>
  <Parent.Resources>

  <!-- These will all inherit the Style resource now,
       without explicit style setting individually. -->
  <TextBlock/>
  <TextBlock/>
  <TextBlock/>

</Parent>