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Editorial Team
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Asked: 2026-05-16T11:19:12+00:00

I have a simple app that consists of: Model Items Filter criteria applied to

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I have a simple app that consists of:

Model

  • Items
  • Filter criteria applied to that list of items

Views

  • WelcomePage
  • MainItemsPage
  • FilterEditPage

I am using MVVM Light and Windows Phone 7

I currently have 3 ViewModels, one for each View. In the past I have had a single ViewModel which made the comunication which I am about to ask about very easy. However I wanted to go with the 3 seperate VMs as that seems to be the correct way.

The WelcomePage is able to set one of the Filter criteria before navigating to the MainItemsPage. The MainItemsPage is bound to an Items property that is exposed by its ViewModel. That ViewModel needs to have filtered that list depending on the current filter criteria. The FilterEditPage allows the user to edit the full criteria set of 4 variables. When the criteria is changed the Items collection used in the ViewModel for MainItemsPage needs to be refiltered.

The question is how I flow the Filter changes through the app. I know that MVVM has the concept of Messaging and the MVVM Light toolkit provides the Messenger class. However what I am struggling with is where does the responsibility lie for sending those messages?

  1. Do the 3 VMs go to the Model whenever they need to work with the current Filter set?
  2. Do all Filter updates go through the FilterEditViewModel and that in turn broadcasts a filter change message?
  3. Do I go back to a single VM for all the Views?

I cannot see 1. working because something will need to trigger the VMs to go back to the Model
I know I can get 3. working right now with no problem. Is it that wrong?

TIA

Pat Long

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1 Answer

  1. Editorial Team

    I would put the shared current filter in the Model not the view model. You’ve got lots viewModels potentially on different pages or on the same page (consider a breadcrumb showing current selection and something else that needs to show a filter has been applied).

    How about a singleton model for the Filter that view models can subscribe to?

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