It seems like the trigger Collection do not accept custom triggers in .NET 3.5 (it's actually working in 4.0)
However, you don't need to inherit the DataTrigger class if you just want to add a Description property. That's what Attached Properties are for :)
Define this attached property in your Control1.xaml.cs :
public static string GetDescription(DependencyObject obj)
{
return (string)obj.GetValue(DescriptionProperty);
}
public static void SetDescription(DependencyObject obj, string value)
{
obj.SetValue(DescriptionProperty, value);
}
// Using a DependencyProperty as the backing store for Description. This enables animation, styling, binding, etc...
public static readonly DependencyProperty DescriptionProperty =
DependencyProperty.RegisterAttached("Description", typeof(string), typeof(Control1), new UIPropertyMetadata(string.Empty));
And simply set it in you xaml :
<DataTrigger dc:Control1.Description="Background Color Trigger Where Value Is Greater Than 100">