UserControl in DataTemplate doesn't applied style for font - wpf

Question

I have a user control in a DataTemplate, The Style of a TextBlock doesn't change the FontSize but changes the Background.
Attached are the samples:
Create a WPF window.
Create a User control, UserControl1
Inside the Window paste the below code:
<Window.Resources>
<Style TargetType="{x:Type TextBlock}"
x:Key="TextBlockStyleFontAndBackgound">
<Setter Property="FontSize"
Value="20" />
<Setter Property="Background"
Value="Blue" />
</Style>
<DataTemplate x:Key="contentTemplate">
<StackPanel>
<m:UserControl1 />
</StackPanel>
</DataTemplate>
</Window.Resources>
<Grid>
<ContentControl FontSize="10">
<StackPanel x:Name="stackPanel">
<Button Click="Button_Click" />
<ContentControl ContentTemplate="{StaticResource contentTemplate}" />
<!--<m:UserControl1 />-->
</StackPanel>
</ContentControl>
</Grid>
In the user control paste the following code:
<UserControl.Resources>
<DataTemplate x:Key="contentTemplateInsideUserControl">
<TextBlock Name="textBlockInResourse" Text="textBlockInsideUserControlResource"
Style="{DynamicResource TextBlockStyleFontAndBackgound}"/>
</DataTemplate>
</UserControl.Resources>
<Grid>
<StackPanel>
<ContentControl ContentTemplate="{StaticResource contentTemplateInsideUserControl}" />
<Button Content="St" Click="Button_Click" />
<TextBlock Name="textBlockInControl" Text="textBlockInsideUserControl"
Style="{DynamicResource TextBlockStyleFontAndBackgound}" />
</StackPanel>
</Grid>
We have 2 text blocks with the same background color, blue, but with different font sizes.
textBlockInResourse FontSize = 20, taken from the style TextBlockStyleFontAndBackgound
textBlockInControl FontSize = 10, inherited value, why does it happen?
I have added a handle in the user control:
private void Button_Click(object sender, RoutedEventArgs e)
{
Style style = FindResource("TextBlockStyleFontAndBackgound") as Style;
textBlockInControl.Style = null;
textBlockInControl.Style = style;
}
And now the Font is set to the style TextBlockStyleFontAndBackgound, and it's size is 20
Why now the FontSize is taken from the style TextBlockStyleFontAndBackgound.
Thanks,
barak

Answer 1

That's a very peculiar problem you have found there. I'm not sure why the FontSize is not affected when not in a DataTemplate... looking at the two property descriptions and remarks on MSDN, the only difference between them is that TextBlock.FontSize is also an AttachedProperty, but I can't see how that would affect anything.
I can however offer a solution to the problem if you're still interested. Try declaring your Style in your App.xaml file:
<Application.Resources>
<Style TargetType="{x:Type TextBlock}" x:Key="TextBlockStyleFontAndBackgound">
<Setter Property="FontSize" Value="20" />
<Setter Property="Background" Value="Blue" />
</Style>
</Application.Resources>
Then declare your TextBlock in your UserControl using StaticResource like so:
<TextBlock Text="text" Style="{StaticResource TextBlockStyleFontAndBackgound}" />