callbackbased

Callback based communication

This way of communicating is very similar to interface based. Instead of passing an interface, it will pass Actions. The Actions can then be invoked in the appropriate places

The idea

MainViewModel is the glue between IFriendsViewModel and IHairColorCountingViewModel. So, each IFriendViewModel has to tell MainViewModel that its hair color has changed, that way it can tell HairColorCountingViewModel to reevaluate.

MainViewModel should pass an Action to FriendsViewModel, which then passes that Action for each FriendViewModel. The FriendViewModel should invoke the action when changing it's hair color.

How did I implement it?

Expanded the constructor of FriendViewModel with Action OnFriendChanged. Saves the action in a backing field (m_onFriendChanged).

FriendViewModel invokes m_onFriendChanged in HairColor setter.

Expanded FriendsViewModel.Initialize with an Action OnFriendChanged.

MainViewModel sends EvaluateHairColor to FriendsViewModel.Initialize.

FriendsViewModel sends OnFriendChanged to each FriendViewModel constructor.

Summary

This pattern is very similar to ìnterface based, and is probably more suitable for smaller projects with not that much communication. But this can be troublesome when dealing with loads of communication. I believe that having interfaces that can be expanded is better than having to send many actions back and forth. It is also not strongly typed, so you could be facing bugs where you send the wrong action down the line. This can be fixed with using an Action<MyArgumentClass>, that way you are strongly typed.