void Attach()
        {
            _contentTemplateProperty.Attach(OnContentTemplateChanged);
            _contentProperty.Attach(OnContentChanged);

            TemplateControlProperty.Attach(OnTemplateControlChanged);
            IsExpandedProperty.Attach(OnExpandedChanged);
        }
 void Attach()
 {
     _contentTemplateProperty.Attach(OnContentTemplateChanged);
     _contentProperty.Attach(OnContentChanged);
     HorizontalContentAlignmentProperty.Attach(OnContentAlignmentChanged);
     VerticalContentAlignmentProperty.Attach(OnContentAlignmentChanged);
     TemplateControlProperty.Attach(OnTemplateControlChanged);
 }