Binding a DependencyPropery to an IRelayCommand<T>

[thomasrea0113]

I've create a simply project to demonstrate my issue. Basically, I have a custom UserControl that exposes a DependencyProperty, which is bound to the Window view model (an ObservableObject). I'm looking for a way for a UserControl to make modifications to another view model via an ICommand parameter, so as to not have to directly couple the control to the window.

My actual use case is a separate AddItemUserControl, which will add an item to an ObservableCollection, without the AddItemUserControl needing to have a direct reference to the collection. Instead, the collection is passed as a parameter to some AddItemCommand on the user control. The Collection is then bound as a DependencyProperty on the user control, where the binding points back to the Window's view model collection.

The simple project I've created to demonstrate my issue, simply binds a string from the window to the command parameter, and then uses it to update a TextBox in the control. The same issue exists - the DepedencyProperty is not being bound to the value that I am setting

https://github.com/thomasrea0113/wpf-DependencyProperty-bind

I realize this may be a code-smell, and am open to alternative solutions. Thanks!