was introduced in Prism-v2 and the post you mention from Julian Dominguez targets Prism-v1. On the other hand, when you create regions by code region behaviors are not attached. As Julian says in his post:
"One drawback of this particular implementation is that if I have a more complex Control that not only binds, but interacts with a region,
there is no out-of-the-box behavior that will use Region Adapters
to enhance this binding (in the example the ItemsControl just binds to the Views collection exposed by the region and that’s it)."
To workaround this issue you might register the
AutoPopulateRegionBehavior (which is in charge of listening to the
IRegionViewRegistry changes and populate the region content) for the regions you create by code (this is automatically done by region adapters when regions are registered in XAML). The code should be similar to the following:
SubMenuRegion = new Region();
Depending on your scenario, you might need to register other behaviors. You can find prism behaviors in the
Region/Behaviors folder of the Composite.Presentation.Desktop project.
You can also you the IRegionBehaviorFactory to get the default behaviors
Hope it helps!