Question

I have the following property definition:

public static class Extensions
{
    public static readonly DependencyProperty TestProperty = DependencyProperty.RegisterAttached("Test", typeof(Storyboard), typeof(UIElement), new UIPropertyMetadata(null));

    public static void SetTest(UIElement element, Storyboard value)
    {
         element.SetValue(TestProperty, value);
    }

    public static Storyboard GetTest(UIElement element)
    {
         return (Storyboard)element.GetValue(TestProperty);
    }
}

And try it use in the xaml

<UserControl
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:Application;assembly=Application"
    x:Name="template"
    Height="40" Width="1460">
    <Grid Background="#FF000000">
        <TextBlock Foreground="White" VerticalAlignment="Center" HorizontalAlignment="Left" TextAlignment="Left" FontSize="32">Example</TextBlock>
    </Grid>
    <UserControl.Style>
        <Style>
            <Setter Property="local:Extensions.Test">
                <Setter.Value>
                    <Storyboard>
                        <DoubleAnimation Storyboard.TargetName="template" From="270" To="360" Duration="0:0:1" Storyboard.TargetProperty="Angle" />
                    </Storyboard>
                </Setter.Value>
            </Setter>
         </Style>
    </UserControl.Style>
</UserControl>

when i try to load such xaml (for example using XamlReader.Load(stream);), i get the exception with the following message

‘local:Extensions.Test’ property is not a valid DependencyProperty on the type ‘Application.Extensions’. Verify that the property has a DependencyProperty defined with a member field that ends with the ‘Property’ suffix. Error at object ‘System.Windows.Setter’.

Can anybody help me with this problem?

thanks in advance!

Answer 1

The owner type should be Extensions instead of UIElement:

public static readonly DependencyProperty TestProperty =
    DependencyProperty.RegisterAttached(
        "Test",
        typeof(Storyboard),
        typeof(Extensions), // here
        new UIPropertyMetadata(null)); 

Could also be written without metadata:

public static readonly DependencyProperty TestProperty =
    DependencyProperty.RegisterAttached(
        "Test",
        typeof(Storyboard),
        typeof(Extensions));