public override void UpdateValue ()
{
if (PropertyInfo != null) {
ValueType = PropertyInfo.PropertyType;
Value = PropertyInfo.GetValue (Source, null);
} else if (DependencyProperty != null) {
ValueType = DependencyProperty.PropertyType;
Value = ((DependencyObject) Source).GetValue (DependencyProperty);
} else {
ValueType = null;
Value = null;
}
}
}