How to send parameters between viewmodels using viewmodellocator

Question

I am creating a WPF application using MVVMLight. I use ViewModelLocator to create viewmodels. My problem is passing parameters between them.

For example we have a situation:

We have a grid with some entities, when one of them is doubleclicked I need to create a new view with details of that entity. How to send the selected item id to ViewModel of the new View?

Flossieflossy

Hi are you using any MessagingServices Like that of Galasoft or any Messaging to Communicate from ViewModel to View – Cinthiacintron

Answer 1

Typically you would use some kind of messaging system, such as Prism's EventAggregator or MVVM Light's Messenger.

Both systems remind me of a paging system: any part of the application can broadcast messages, and any part of the application and subscribe to listen for messages.

So your DoubleClick command would broadcast a LoadItemMessage containing the selected item Id, and whatever is responsible for showing the item would subscribe to receive LoadItemMessages and would load the item whenever it hears a LoadItemMessage.

If you're interested, I have a brief article on my blog about Communication between Viewmodels with MVVM that gives a high level overview of event systems.

Butyraldehyde

Thanks, I knew a little about messaging system but your article made things simple – Flossieflossy

Answer 2

That is a problem with ViewModelLocator (to pass the parameters to ViewModel from View xaml). What you can do is Create a Property Parameter of Type object or (of type your SelectedItem) in ViewModelLocator class. Bind this to the SelectedItem of your Grid and then pass it to your new ViewModel. I hope this will help. NOte: If you create the property of type object don't forget to cast it.

Cinthiacintron

If I understand you correctly your approach can work but it will be very difficult to manage a huge system. Could you please provide some code sample to help me understand. Thanks – Flossieflossy