MVVM - what is the ideal way for usercontrols to talk to each other

Question

I have a a user control which contains several other user controls. I am using MVVM. Each user control has a corresponding VM. How do these user controls send information to

Answer 1

As others have said you have a couple of options.

Exposing DepedencyProperties on your user controls and binding to those properties provides a pure XAML solution in most cases but can introduce some UI dependencies in order for the bindings to see each other

The other option is a decoupled messaging pattern to send messages between ViewModels. I would have your user controls bind to properties on thier own VM's and then on the property change inside that VM it can "publish" a message that notifies other "subscribers" that something has happened and they can react to that message however they want to.

I have a blog post on this very topic if it helps: http://www.bradcunningham.net/2009/11/decoupled-viewmodel-messaging-part-1.html