如何为ItemTemplate和ItemsSource实现可附加属性

I am trying to use the WPF Grid as an ItemsControl using attached properties for the purposes of creating a scalable Piano Keyboard. Each key in the keyboard may span 1 to three columns depending upon what precedes and succeeds it and will span 1 row if sharp or 2 if natural. I already have 2 attached properties for setting the Grid's Column Count and Row Count dynamically (albeit these will need to be adjusted to support the setting of each column/row's width/height).I am trying to use the WPF Grid as an ItemsCont