How to animate Opacity of a DropShadowEffect?

Question

I have a WPF project with a border using the following style. The plan is to get the glow effect to fade in when the mouse moves over the border, and fade out when it leaves.

<Style x:Key="BorderGlow" TargetType="Border">
    <Style.Resources>
        <Storyboard x:Key="GlowOn">
            <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetProperty="(DropShadowEffect.Opacity)">
                <SplineDoubleKeyFrame KeyTime="0:0:0.3" Value="1"/>
            </DoubleAnimationUsingKeyFrames>
        </Storyboard>
        <Storyboard x:Key="GlowOff">
            <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetProperty="(DropShadowEffect.Opacity)">
                <SplineDoubleKeyFrame KeyTime="0:0:0.3" Value="0"/>
            </DoubleAnimationUsingKeyFrames>
        </Storyboard>
    </Style.Resources>

    <Setter Property="CornerRadius" Value="6,1,6,1" />
    <Setter Property="BorderBrush" Value="{StaticResource SelectedBorder}" />
    <Setter Property="BorderThickness" Value="1" />
    <Setter Property="Background" Value="{StaticResource DeselectedBackground}" />
    <Setter Property="RenderTransformOrigin" Value="0.5,0.5" />
    <Setter Property="TextBlock.Foreground" Value="{StaticResource SelectedForeground}" />

    <Setter Property="RenderTransform">
        <Setter.Value>
            <RotateTransform Angle="90"/>
        </Setter.Value>
    </Setter>

    <Setter Property="Effect">
        <Setter.Value>
            <DropShadowEffect ShadowDepth="0" BlurRadius="8" Color="#FFB0E9EF"/>
        </Setter.Value>
    </Setter>

    <Style.Triggers>
        <Trigger Property="IsMouseOver" Value="True">

            <Trigger.EnterActions>
                <BeginStoryboard Storyboard="{StaticResource GlowOn}"/>
            </Trigger.EnterActions>

            <Trigger.ExitActions>
                <BeginStoryboard Storyboard="{StaticResource GlowOff}"/>
            </Trigger.ExitActions>

        </Trigger>
    </Style.Triggers>
</Style>

The problem is, nothing happens! The animation works if I change the "DropShadowEffect" to "UIElement" in the Storyboard TargetProperty, but this fades the entire control.

How do I fade just the DropShadowEffect?

Answer 1

A couple of points to note

1) You need to be targeting an actual property of Border - You are in effect trying to target the value (DropShadowEffect) of the Effect property, not the property itself.

2) You need to sort the syntax of the PropertyPath.

Change your Storyboard.Target property to the following and you should be fine:

Storyboard.TargetProperty="(Effect).Opacity"

EDIT Working code as noted in comment:

<Border BorderThickness="10" Height="100" Width="100">
    <Border.BorderBrush>
        <SolidColorBrush Color="Red"></SolidColorBrush>
    </Border.BorderBrush>
    <Border.Style>
        <Style TargetType="Border">
            <Style.Resources>
                <Storyboard x:Key="GlowOn">
                    <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" 
                          Storyboard.TargetProperty="(Effect).Opacity">
                        <SplineDoubleKeyFrame KeyTime="0:0:0.3" Value="1"/>
                    </DoubleAnimationUsingKeyFrames>
                </Storyboard>
                <Storyboard x:Key="GlowOff">
                    <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" 
                          Storyboard.TargetProperty="(Effect).Opacity">
                        <SplineDoubleKeyFrame KeyTime="0:0:0.3" Value="0"/>
                    </DoubleAnimationUsingKeyFrames>
                </Storyboard>
            </Style.Resources>

            <Setter Property="CornerRadius" Value="6,1,6,1" />
        <!--<Setter Property="BorderBrush"
                    Value="{StaticResource SelectedBorder}" />-->
            <Setter Property="BorderThickness" Value="1" />
        <!--<Setter Property="Background"
                    Value="{StaticResource DeselectedBackground}" />-->
            <Setter Property="RenderTransformOrigin" Value="0.5,0.5" />
        <!--<Setter Property="TextBlock.Foreground"
                    Value="{StaticResource SelectedForeground}" />-->

            <Setter Property="RenderTransform">
                <Setter.Value>
                    <RotateTransform Angle="90"/>
                </Setter.Value>
            </Setter>

            <Setter Property="Effect">
                <Setter.Value>
                    <DropShadowEffect ShadowDepth="20"
                                      BlurRadius="8"
                                      Color="#FFB0E9EF"/>
                </Setter.Value>
            </Setter>

            <Style.Triggers>
                <Trigger Property="IsMouseOver" Value="True">

                    <Trigger.EnterActions>
                        <BeginStoryboard
                              Storyboard="{StaticResource GlowOn}"/>
                    </Trigger.EnterActions>

                    <Trigger.ExitActions>
                        <BeginStoryboard
                              Storyboard="{StaticResource GlowOff}"/>
                    </Trigger.ExitActions>

                </Trigger>
            </Style.Triggers>

        </Style>
    </Border.Style>
</Border>