Communicate two view models in WPF MVVM [closed]

Question

I am developing a WPF application and I have some problems to communicate one view model with another.

I have:

1. MainViewModel
2. ChildViewModel1
3. ChildViewModel2

Every time a property changes in MainViewModel, ChildViewModel1 and ChildViewModel2 should get notified.

Can anyone suggest a workaround?

EDIT: I am thinking in a solution descrided MVVM Light (http://simplemvvmtoolkit.codeplex.com/SourceControl/changeset/view/23821#313594.), that is implementing a message bus. Is it the right approach?

Answer 1

the common way for viewmodels to communicate between themselves is implimentation of theMediator design pattern

here is how it is done in MVVMLight http://social.msdn.microsoft.com/Forums/en-US/wpf/thread/27aaefff-e463-451c-87d9-37367a343e0e

in Prism is: http://blogs.u2u.be/diederik/post/2011/01/15/Using-the-Prism-40-Event-Aggregator.aspx

in Caliburn is: http://www.mindscapehq.com/blog/index.php/2012/02/01/caliburn-micro-part-4-the-event-aggregator/

Answer 2

In most cases I would NOT suggest using any centralized place to share "events"/"notifications", like EventAggregator, etc.. This leads to later issues related with not clear relations between ViewModels. Such notifications makes sense in very specific cases when relations between listener/publisher is not known even on design stage. I would suggest draw simple diagram with relations between ViewModels and find a way of using standard .NET events, so when you have clear realtionships between ViewModels like ViewModel1 has a reference to ViewModel2 so can subscribe to an event or provide own callback, so it will be easy to build such event notifications.

Answer 3

I would use a IService that is implemented by each view model. Then in the view models you can pass the service properties to properties of the view model that implement INotifypropertychanged. For example, I have a service called INavigationService that is implemented by my view models and it has properties like CanNavigate, currentView etc that I bind to in my view models. Changes to these properties can cause navigation or change properties that other view models are binding to.