问题
I am using version 3.0.3.19 of the MVVM Light Toolkit.
From http://blog.galasoft.ch/archive/2010/03/16/whatrsquos-new-in-mvvm-light-v3.aspx:
Messages can now be sent through the Messenger with a token.
To send a message with token, use the method overload Send(TMessage message, object token).
To receive a message with token, use the methods Register(object recipient, object token, Action action) or Register(object recipient, object token, bool receiveDerivedMessagesToo, Action action)
The token can be a simple value (int, string, etc…) or an instance of a class. The message is not delivered to recipients who registered with a different token, or with no token at all.
According to the documentation above, I have tried the following in ViewModel A:
Messenger.Default.Send(new NotificationMessage("message"), "token");
Along with the following in ViewModel B:
Messenger.Default.Register<NotificationMessage>(this, "token", (msg) => Console.WriteLine(msg.Notification));
However, the callback is never executed. What am I doing wrong?
回答1:
My ViewModelLocator was initializing ViewModel A before ViewModel B. In other words, the message was being sent properly by ViewModel A, but ViewModel B was not yet around to actually receive it.
I changed the order of initialization in the ViewModelLocator and the problem was solved. Also, verified that the Messenger worked with tokens of other types besides String.
来源：https://stackoverflow.com/questions/11804050/what-is-the-proper-way-to-use-tokens-with-the-messenger-class