Updating another ViewModel on PropertyChanged of another ViewModel

Question

Both ViewModels know nothing about each other, but i need to send the new value that have changed in one viewmodel to a method in the other view model, what are my options?

could you please list all possibilities and what would be the best way?

See [my answer](http://stackoverflow.com/a/19191496/643085) to a similar question. — Federico Berasategui, Oct 07 '13 at 22:46
yes, if you don't want to have a reference from one ViewModel to the other. — Federico Berasategui, Oct 07 '13 at 22:49
I would recommend an Event Aggregator. @HighCore linked to one. There are any number of examples once you know what to search for. — Kevin, Oct 07 '13 at 22:50
@HighCore Thank you :) it worked as it should ,please feel free to write an answer, but i still wonder why you called it DumbAggregator, what could a smarter one do? — FPGA, Oct 07 '13 at 23:13

score 3 · Accepted Answer · edited May 23 '17 at 12:00

Taken from this answer:

If you want loosely-coupled communication you need an EventAggregator:

//Simplest EventAggregator
public static class DumbAggregator
{
    public static void BroadCast(string message)
    {
       if (OnMessageTransmitted != null)
           OnMessageTransmitted(message);
    }

    public static Action<string> OnMessageTransmitted;
}

Usage:

public class MySender
{
   public void SendMessage()
   {
       DumbAggregator.BroadCast("Hello There!");
   }
}

public class MySubscriber
{
   public MySubscriber()
   {
       DumbAggregator.OnMessageTransmitted += OnMessageReceived;
   }

   private void OnMessageReceived(string message)
   {
      MessageBox.Show("I Received a Message! - " + message);
   }
}

Notice however, that EventAggregators included in MVVM frameworks such as Prism are much more complex and include a whole lot of functionality. This is just a simple example.

Updating another ViewModel on PropertyChanged of another ViewModel

1 Answers1