Very strange problem in Silverlight with XAML, custom property and animation - silverlight

Question

I created a custom user control that has a property of type Storyboard. Something like:
public class UC : UserControl
{
public static readonly DependencyProperty AnimationProperty = DependencyProperty.Register(
"Animation",
typeof(Storyboard),
typeof(UC),
null);
public Storyboard Animation
{
get { return (Storyboard)GetValue(AnimationProperty); }
set { SetValue(AnimationProperty, value); }
}
public UC()
{
this.Loaded += new RoutedEventHandler(UC_Loaded);
}
private void UC_Loaded(object sender, RoutedEventArgs e)
{
if (this.Animation != null)
{
this.Animation.Begin();
}
}
}
In XAML I used it as follows:
<loc:UC x:Name="uc" Opacity="0" >
<TextBlock FontSize="50">Some text</TextBlock>
<loc:UC.Animation>
<Storyboard>
<DoubleAnimation Storyboard.TargetName="uc" Storyboard.TargetProperty="Opacity" To="0.5" Duration="0:0:1" />
</Storyboard>
</loc:UC.Animation>
</loc:UC>
So far so good.
Later on I decided that I needed another item along with the storyboard. So I changed the code to accept a custom object that contains the storyboard and another piece of information. Something like:
public class UC : UserControl
{
public static readonly DependencyProperty AnimationProperty = DependencyProperty.Register(
"Animation",
typeof(AnimationHolder),
typeof(UC),
null);
public AnimationHolder Animation
{
get { return (AnimationHolder)GetValue(AnimationProperty); }
set { SetValue(AnimationProperty, value); }
}
public UC()
{
this.Loaded += new RoutedEventHandler(UC_Loaded);
}
private void UC_Loaded(object sender, RoutedEventArgs e)
{
if (this.Animation != null)
{
this.Animation.Animation.Begin();
}
}
}
public class AnimationHolder
{
public Storyboard Animation
{
get;
set;
}
public int OtherValue
{
get;
set;
}
}
And used it in XAML:
<loc:UC x:Name="uc" Opacity="0" >
<TextBlock FontSize="50">Some text</TextBlock>
<loc:UC.Animation>
<loc:AnimationHolder OtherValue="20">
<loc:AnimationHolder.Animation>
<Storyboard>
<DoubleAnimation Storyboard.TargetName="uc" Storyboard.TargetProperty="Opacity" To="0.5" Duration="0:0:0" />
</Storyboard>
</loc:AnimationHolder.Animation>
</loc:AnimationHolder>
</loc:UC.Animation>
</loc:UC>
However, now when I try to begin the animation I get an InvalidOperationException with the message: "Cannot resolve TargetName uc."
Anyone has an idea why?
I know that in this example I can work around the problem by not using a custom object, and using another property instead. However this is a simplified version of my scenario, which focuses at the problem. In the real scenario I must use a custom object.

Answer 1

Two things need to be done with your new approach:
In AnimationHolder class, make Animation property a dependency property, just like it previously was.
Derive AnimationHolder class from DependencyObject. This is necessary so that you can make Animation a dependency property. Please remember that only classes deriving from DependencyObject can define dependency properties!
I think once you do these two things, it'll solve your problem!