Question

I’ve seen many Tutorials about the MVVM-Patern but I still don’t get why I need to get a Dependency-Property or an INotiyfyPropertyChanged-Property if I want to send information from the ViewModel back to the View.

Answer 1

Dependency properties provide built in change notification for when a property changes which means WPF knows when a controls value has changed.

Your ViewModel types do not, by default, provide any mechanism for change notification so if they don’t support either of these options how is the view supposed to know when a property in your viewModel has been changed?

You need your viewModel to use either of these options so that the view can be notified when a property value changes.

This means if a property value is changed in code, the user interface is updated and if a property is changed by user input your viewModel (and ultimately your model) is also updated to reflect these changes. (basically both sides of a binding require a way of communicating a property change to each other).

The INotifyPropertyChanged interface is the preferred method as it means your viewModels are not specific to WPF and can be used by other user interface technologies. also, dependency properties can only be used in types that derive from DependencyObject.