Question

loosly coupled communication between viewmodels is a nice concept.
I have used Prism Eventaggregator as well as MVVM Light Toolkit’s Messanger.

If the project grows I get alot of messages back and forth.

What is best practise of keeping track of my messages? Naming conventions? patterns?
etc…
How do you keep track?

Answer 1

I’ve found that there is a lot of value in providing a “Messages” namespace that contains your strongly typed messages. Keep in mind that well-defined messages will be more like contracts/DTOs – you want to maintain as much decoupling as possible, so dependencies should be kept to a minimum, otherwise the senders and receivers will both rely on common libraries. Sometimes this is necessary due to the nature of the message.

I think you’ll also find that many messages may follow a particular pattern. Two common message patterns are what I’ll call the Action and Command. Action is more of a “verb” and a “subject”.

For example, you might have MessageAction that exposes T Target, and the action is an enumeration that indicates update, select, add, delete, etc. That’s common and a generic message can wrap it, and your handlers listen for the generics that close the type they are interested in.

The Command is an Action that originates from somewhere and then applies an action to a target. For example, maybe you are adding a role to a user. In that case, your item of interest is the role, your target is the user, and your action is adding it. That can be a CommandAction.

Another common way to organize messages would be to implement a common interface or base class. It then becomes trivial to search for implementors in the project to determine where messages are being used.