在Uwp VisualState.Setters中使用StaticResource

Question

This is my code

<VisualState x:Name="Focused">
  <VisualState.Setters>
    <Setter Property="Background" Value="{StaticResource LightButtonBackground}"/>
    <Setter Property="Foreground" Value="White" />
  </VisualState.Setters>
</VisualState>

The compiler says XamlCompiler error WMC0615: Type 'StaticResource' used after '{' must be a Markup Extension. Error code 0x09ff. XamlCompiler error WMC0615: Type 'StaticResource' used after '{' must be a Markup Extension. Error code 0x09ff. I didn't find any useful information on the network. What's wrong?

Answer 1

You're mixing the two usages of the Setter here.

The Property property can be used only when defining a Style :

    <Style TargetType="TextBlock" x:Key="TextBlockStyle">
        <Setter Property="Foreground" Value="Navy"/>
        <Setter Property="FontSize" Value="14"/>
        <Setter Property="VerticalAlignment" Value="Bottom"/>
    </Style>

In a style definition the targeted control type is already known (It is provided by Style.TargetType ).

In a VisualState.Setters list, you are not defining a Style . You are altering some properties on some existing child controls . In this case, you need to use the Target property to let the XAML runtime know which element and properties you are targeting.

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <VisualStateManager.VisualStateGroups>
        <VisualStateGroup>
            <VisualState x:Name="NarrowState">
                <VisualState.Setters>
                    <Setter Target="myPanel.Orientation" Value="Vertical"/>
                    <Setter Target="myPanel.Width" Value="380"/>
                    <Setter Target="myTextBlock.MaxLines" Value="3"/>
                </VisualState.Setters>
            </VisualState>
        </VisualStateGroup>
    </VisualStateManager.VisualStateGroups>

    <StackPanel x:Name="myPanel" Orientation="Horizontal">
        <TextBlock x:Name="myTextBlock" MaxLines="5" Style="{ThemeResource BodyTextBlockStyle}"/>
    </StackPanel>
</Grid>

Answer 2

As @Vincent answer points out, you are not utilizing the setter correctly when defining it inside a visual state, but instead utilizing as you would when defining a style resource. Nevertheless my answer is an insight on how you can utilize a defined StaticResource on a style, analyzing the two situations and whether it is possible or not.

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With that said, I don't think it's possible to define a property of a style by setting it onto a resource.

• What would happen if you were defining more than one property on your resource? How would you then be able to set a property style to that resource holding multiple styled properties?
• What would happen if you defined a resource holding a Color for the background, but you then use that resource to set it as the foreground of your dependency object control? Should that flexibility exist, since you are targeting a property which accepts the same type?

What you are actually looking for is the BasedOn , property which allows to inherit styles. The only downside is that Styles that inherit from other styles must target the same type of control or either a control that derives from the type targeted by the base style.

Take a look onto the documentation, here: https://docs.microsoft.com/en-us/windows/uwp/design/controls-and-patterns/xaml-styles#use-based-on-styles

Edit:

Unfortunately, I don't think it's possible to define your VisualState style to inherit from a resource using the BasedOn , since we are forced to specify every setter on its definition. Might we be under an XY problem ? On a resource definition, that would be the way to go if you want to inherit from a style, but actually applying it on a visual state seems to be another completely story.