Usercontrol properties in Styles - silverlight

Question

I have a usercontrol that expose a public property like this :
public Double ButtonImageHeight
{
get { return imgButtonImage.Height; }
set { imgButtonImage.Height = value; }
}
when I use that control, I want to be able to set that property throught a Style like that :
<Style x:Key="MyButtonStyle" TargetType="my:CustomButtonUserControl" >
<Setter Property="ButtonImageHeight" Value="100" />
</Style>
What am I doing wrong?
Thanks

Answer 1

thanks Matt, I just found it myself but you were absolutely right... here's the exact code I used in case it can help someone else (all the examples I found were on WPF, silverlight is just slightly different) :
public static readonly DependencyProperty ButtonImageHeightProperty = DependencyProperty.Register("ButtonImageHeight", typeof(Double), typeof(CustomButtonUserControl),new PropertyMetadata(ButtonImageHeight_PropertyChanged ));
public Double ButtonImageHeight
{
get { return (Double)GetValue(ButtonImageHeightProperty); }
set { SetValue(ButtonImageHeightProperty, value); }
}
private static void ButtonImageHeight_PropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
((CustomButtonUserControl)source).imgButtonImage.Height = (Double)e.NewValue;
}

Answer 2

The property needs to be a dependency property in order to support styles.

Answer 3

You can make it even more generic and nice by passing through a Style for your imgButtonImage, that way you can set multiple properties. So within your user control add the dependency property, but make it a Style:
public static readonly DependencyProperty UseStyleProperty =
DependencyProperty.Register("UseStyle", typeof(Style), typeof(CustomButtonUserControl), new PropertyMetadata(UseStyle_PropertyChanged));
public Style UseStyle
{
get { return (Style)GetValue(UseStyleProperty); }
set { SetValue(UseStyleProperty, value); }
}
private static void UseStyle_PropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
((CustomButtonUserControl)source).imgButtonImage.Style = (Style)e.NewValue;
}
Notice how within the PropertyChanged function I set the style of the control to the new style.
Then when I host the UserControl I can pass through the style:
<Style x:Name="MyFancyStyle" TargetType="Button" >
<Setter Property="FontSize" Value="24" />
</Style>
<controls:MyUserControl UseStyle="{StaticResource MyFancyStyle}" />
works in VS design mode too! (It's a miracle)