Bind to a property in a ResourceDictionary

Question

I have a Templates.xaml file in my project which contains the ResourceDictionary of styles.

I want to bind Direction of a DropShadowEffect to MyNamespace.MyPage.LightDirection. Currently I did this:

// MyPage.xaml.cs
/// <summary>
/// Direction of light source for shadows and gradients.
/// </summary>
public static double LightDirection => 45;

<!--Templates.xaml-->
<Style x:Key="ControlButtons" TargetType="{x:Type Button}">
    <Setter Property="Effect">
        <Setter.Value>
            <DropShadowEffect ShadowDepth="4" Direction="{Binding LightDirection}" Color="Black" Opacity="0.5" BlurRadius="4" />
        </Setter.Value>
    </Setter>
    <!--Other Setters-->
</Style>

<!--MyPage.xaml-->
<Page x:Name="MyPage"
      DataContext="{Binding ElementName=MyPage}">
      <!--MyPage as some other default attributes which I didn't write here-->
    <Grid>
        <Button x:Name="MyButton" Style="{StaticResource ControlButtons}">
            My Button
        </Button>
    </Grid>
</Page>

It works. The shadow direction is set to LightDirection and program runs normally. However, while debugging, debugger shows a binding error:

Cannot find governing FrameworkElement or FrameworkContentElement for target element.

What is my mistake? How should I prevent this error?

Answer 1

I suggest making a constant

namespace MyNamespace
{
    public class Constants
    {
        public static double LightDirection { get; set; }
    }
}

XAML

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"                
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:local="clr-namespace:MyNamespace">
    <Style x:Key="ControlButtons" TargetType="{x:Type Button}">
        <Setter Property="Effect">
            <Setter.Value>
                <DropShadowEffect ShadowDepth="4"
                                  Direction="{x:Static local:Constants.LightDirection}"
                                  Color="Black"
                                  Opacity="0.5" 
                                  BlurRadius="4" />
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

Or declare constant directly in XAML

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"                
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:local="clr-namespace:MyNamespace"
                    xmlns:sys="clr-namespace:System;assembly=mscorlib" >
    <sys:Double x:Key="LightDirection">45.0</sys:Double>
    <Style x:Key="ControlButtons" TargetType="{x:Type Button}">
        <Setter Property="Effect">
            <Setter.Value>
                <DropShadowEffect ShadowDepth="4"
                                  Direction="{StaticResource LightDirection}"
                                  Color="Black"
                                  Opacity="0.5" 
                                  BlurRadius="4" />
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>