Question

I have a DataTemplate with a number of layered text and graphic objects. One of them is a glow effect that comes from the RadialGradientBrush Fill property of a Rectangle. At first, I named the Rectangle and bound to the Fill property and changed it using a DataTrigger. This worked fine, but I have a number of RadialGradientBrush objects in the Resources section and as you can see below, it is a lot to repeat when all I want to do is change the GradientStops. So I removed the Fill binding and added and named a RadialGradientBrush and although I can bind to the brush from Resources, I can’t access it in the DataTrigger. I get the ‘Cannot find Trigger target’ error.

<Rectangle x:Name="Glow" IsHitTestVisible="False" RadiusX="1.5" RadiusY="1.5" VerticalAlignment="Stretch" HorizontalAlignment="Stretch" StrokeThickness="0" Opacity="1.0">
    <Rectangle.Fill>
        <RadialGradientBrush x:Name="GlowGradient" Center="0.5,0.848" GradientOrigin="0.5,0.818" RadiusX="-1.424" RadiusY="-0.622" GradientStops="{StaticResource DefaultGradient}">
            <RadialGradientBrush.RelativeTransform>
                <TransformGroup>
                    <ScaleTransform CenterX="0.5" CenterY="0.848" ScaleX="1" ScaleY="1.8"/>
                    <SkewTransform AngleX="0" AngleY="0" CenterX="0.5" CenterY="0.848"/>
                    <RotateTransform Angle="-33.418" CenterX="0.5" CenterY="0.848"/>
                    <TranslateTransform Y="0.278"/>
                </TransformGroup>
            </RadialGradientBrush.RelativeTransform>
        </RadialGradientBrush>
    </Rectangle.Fill>
</Rectangle>

In the resources, I have several RadialGradientBrush objects like this one.

<RadialGradientBrush x:Key="EscalatedGlow" Center="0.5,0.848" GradientOrigin="0.5,0.818" RadiusX="-1.424" RadiusY="-0.622">
    <RadialGradientBrush.RelativeTransform>
        <TransformGroup>
            <ScaleTransform CenterX="0.5" CenterY="0.848" ScaleX="1" ScaleY="1.8"/>
            <SkewTransform AngleX="0" AngleY="0" CenterX="0.5" CenterY="0.848"/>
            <RotateTransform Angle="-33.418" CenterX="0.5" CenterY="0.848"/>
            <TranslateTransform Y="0.278"/>
        </TransformGroup>
    </RadialGradientBrush.RelativeTransform>
    <GradientStop Color="Aqua" Offset="0.168"/>
    <GradientStop Color="#5E1D96FF" Offset="0.474"/>
    <GradientStop Color="#1101FFFF" Offset="1"/>
</RadialGradientBrush>

I want to replace them with less code for each colour change, so I created some GradientStopCollection objects in the Resources to replace them with.

<GradientStopCollection x:Key="EscalatedGradient">
    <GradientStop Color="Aqua" Offset="0.168"/>
    <GradientStop Color="#5E1D96FF" Offset="0.474"/>
    <GradientStop Color="#1101FFFF" Offset="1"/>
</GradientStopCollection>

Although I can bind to the Resource gradients, the problem is that I can’t access the GlowGradient brush to change its GradientStops property. I could previously access the Glow Rectangle using a DataTrigger with the following.

<DataTrigger Binding="{Binding Path=Status}" Value="Escalated">
    <Setter TargetName="Glow" Property="Fill" Value="{StaticResource EscalatedGlow}"/>
</DataTrigger>

When I use the following, I get the ‘Cannot find Trigger target’ error.

<DataTrigger Binding="{Binding Path=Status}" Value="Escalated">
        <Setter TargetName="GlowGradient" Property="GradientStops" Value="{StaticResource EscalatedGradient}"/>
</DataTrigger>

I’m thinking there just has to be a way to save me from replicating the whole RadialGraientBrush each time I want to change the colours. Is there any way to access the Rectangle Fill brush from the DataTrigger? Any tips anyone? Thanks in advance.

Answer 1

In the end, I went with the following code:

<Rectangle Name="Glow" IsHitTestVisible="False" RadiusX="2.5" RadiusY="2.5" 
Fill="{StaticResource OrangeGlow}" />

<Storyboard x:Key="GlowColourStoryboard" TargetName="Glow" Duration="0:0:1.5" 
AutoReverse="True" BeginTime="0:0:0" RepeatBehavior="Forever">
    <ColorAnimation Storyboard.TargetProperty="Fill.GradientStops[0].Color" 
To="{StaticResource RedGradient.Colour1}" />
    <ColorAnimation Storyboard.TargetProperty="Fill.GradientStops[1].Color" 
To="{StaticResource RedGradient.Colour2}" />
    <ColorAnimation Storyboard.TargetProperty="Fill.GradientStops[2].Color" 
To="{StaticResource RedGradient.Colour3}" />
</Storyboard>

I haven’t shown the Brush resources because… well you can make your own. This Storyboard is used in the following way and works as required:

<DataTrigger.EnterActions>
    <BeginStoryboard Storyboard="{StaticResource GlowColourStoryboard}" />
</DataTrigger.EnterActions>