'{DependencyProperty.UnsetValue}' is not a valid value for property 'FocusVisualStyle'

Question

I have a weird error I\'m trying to debug with no luck.

I have subclassed hwndhost showing some content, I have the following function in that class to set to fullsc

Answer 1

In case you got here by Googling the question title: Another way to cause this exception is to use a Trigger, but forget to set the Value.

Example:

<ControlTemplate.Triggers>
  <Trigger Property="IsEnabled">
    <Setter Property="Background" Value="Gray" />
  </Trigger>
</ControlTemplate.Triggers>

This causes a XamlParseException where the inner exception reads:

'{DependencyProperty.UnsetValue}' is not a valid value for property 'IsEnabled'.

Correction:

<ControlTemplate.Triggers>
  <Trigger Property="IsEnabled" Value="False">
    <Setter Property="Background" Value="Gray" />
  </Trigger>
</ControlTemplate.Triggers>

Answer 2

my guess is that the control that gets the focus when you close the mentioned window has a custom style set by you that does not include any FocusVisualStyle.

so to help you further, you should explain a bit more: what happens (or should happen) when you close this window?

what control type is supposed to get the focus?

Answer 3

Yet another way to cause mentioned exception is when you declare StaticResource after using it, for example in style declaration.

WRONG

<Style TargetType="Label">
    <Setter Property="Foreground" Value="{StaticResource BlueAccent}"/>
</Style>

<SolidColorBrush x:Key="BlueAccent" Color="#22afed"/>

CORRECT

<SolidColorBrush x:Key="BlueAccent" Color="#22afed"/>

<Style TargetType="Label">
    <Setter Property="Foreground" Value="{StaticResource BlueAccent}"/>
</Style>

Answer 4

This can happen when a Style is pointing to a StaticResource that does NOT exist.

This xaml was failing:

<Grid.Resources>
    <Style TargetType="{x:Type TextBox}">
        <Setter Property="Height" Value="{StaticResource StandardControlHeight}"/>
        <Setter Property="VerticalContentAlignment" Value="Center"/>
    </Style>
</Grid.Resources>

The error was:

System.InvalidOperationException: ''{DependencyProperty.UnsetValue}' is not a valid value for property 'Height'.'

When I added the missing StaticResource, the problem went away.