DialogVisitor

Maintaining the layering of MVVM (Model-View-ViewModel) when displaying a dialog form is challenging, because the command handler in the ViewModel layer needs to somehow access the dialog window without breaking the layering. The ViewModel should not have a compile-time dependency on any View (Windows UI) object, including the View that contains the dialog window, while the dialog window needs to be given a reference to the data it will manipulate, which is not known until runtime. This article describes a simplified approach using a modified Visitor Pattern (Gamma, et al, Design Patterns) and dependency injection (DI) to maintain the separation of layers.