The ElementFlow control was something I was working on a while back and I even posted about it here. The control originally derived from a FrameworkElement and had its own properties for enabling binding to a data-source, namely ElementsSource and ElementTemplate. These properties behave similar to the ItemsSource and ItemTemplate of ItemsControl.
One could argue that instead of deriving from FrameworkElement, I should derive from ItemsControl. That way I would get the Databinding support free of cost. But making ElementFlow an ItemsControl means that I could use any Panel as my ItemsPanel. This ofcourse is NOT true. ElementFlow is primarily meant to visualize items in 3D. This means I would be using Viewport3D and GeometryModels to represent my items. Using any other kind of panel doesn’t really work well and is simply not correct. Also I think it violates the Liskov Substitution Principle (LSP).
However, ItemsControl does take care of data-binding by automatically generating the ContentPresenters for the items in the data-source. That idea led to a philosophical debate with myself, where I was arguing (with myself) that ElementFlow should really be handling layout of the items in 3D and should not worry about the data-source and deciphering DataTemplates. Its primary job is really to layout items in 3D.
The component in WPF that does pure layout is a Panel. Making ElementFlow a Panel was “definitely” the way to go.
Deriving directly from Panel required me to make couple different changes to the control and I also ran into a few issues along the way:
protected override void OnVisualChildrenChanged(DependencyObject visualAdded, DependencyObject visualRemoved)
I make a change to my Viewport3D (adding/removing models) within this method.
Once past those issues, I had ElementFlow working in collaboration with ItemsControl. I can now get all my UI elements from the ItemsControl and not have to worry about data-binding and its related issues (children add/remove/update). This also saves me lot of development and maintenance time, as I rely more on the framework for things its really good at, namely DataBinding!
Note that ElementFlow also works independently of ItemsControl, just like any other Panel :)