Question

Is it right that wpf-objects that are freezable are freezed in any case automatically if they are generated through a DataTemplate, ControlTemplate or a style?

Answer 1

I played a little around with brushes in my VisualTree-Analyzer to see how the automatic freezing works. Here the result of my tests:

All Brushes that were attached through ControlTemplates, DataTemplates or Styles have been frozen, regardless if the declaring Brush in the template or in the style has been frozen.

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For getting this, I checked the resulting visual tree of the following templates and styles:

<DataTemplate x:Key="Test_DataTemplate">
    <Grid> 
        <!-- Explicit creation to ensure Brush is !IsFrozen through the converter-->
        <Grid.Background> 
            <SolidColorBrush Color="Red"/>
        </Grid.Background>
        <TextBlock Text="{Binding}"/>
    </Grid>
</DataTemplate>

<ControlTemplate x:Key="Test_ControlTemplate"  TargetType="{x:Type ContentControl}">
    <Border >
        <Border.Background>
            <SolidColorBrush Color="Green" />
        </Border.Background>
        <ContentPresenter />
    </Border>
</ControlTemplate/>

<Style x:Key="Test_Style" TargetType="TextBlock">
    <Setter Property="Background" >
        <Setter.Value>
            <SolidColorBrush Color="Yellow" />                    
        </Setter.Value>                
    </Setter>
</Style>   

<TextBlock >
    <TextBlock.Style>
    <Style TargetType="TextBlock">
        <Setter Property="Background" >
            <Setter.Value>
                <SolidColorBrush Color="Violet" />                    
            </Setter.Value>                
        </Setter>
    </Style>
    </TextBlock.Style>            
</TextBlock>

As already remarked, the Brushes in the visual tree always were frozen.

Furthermore also the Brush of the setter in the style of the style-test was frozen, if the style has been used at least one time. I think this “one-time restriction” is because WPF must test if no animation touches the Brush and it does this on the moment of first use. But that’s only speculative. I haven’t done any test with animation.

Based on elder observations to this topic, I think my initial question may be answered with yes. Such a behavior seems to me also as logical. But it’s clear that so few tests with one type of resource also can lead in a totally wrong direction. Sadly, there’s not a lot of information about this topic available. If someone has some good links, or if I have made an obvious mistake in my simple tests, please leave me a comment.