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How can a ViewModel know when data in a service is being updated?

In my application, I have several ViewModels that have a separate service (repository, DAO, whatever), let me call it the WidgetService introduced in them.

Let's say that one of these ViewModels is a list of all user widgets. Another may be a ViewModel for editing / creating one of these widgets.

The user can view the list of widgets WidgetListView supporting WidgetListViewModel and click a button to add a new widget. To create this new widget, CreateWidgetViewModel is updated and inserted into the DataContext of some UserControl / Window, thus, thanks to the magic of DataTemplates displaying CreateWidgetViewModel in CreateWidgetView . In addition, the innovation of CreateWidgetViewModel does not necessarily occur as part of the WidgetListViewModel .

When the WidgetListViewModel instance of WidgetService was added . CreateWidgetViewModel This WidgetService tag has been added .

Now, when the user clicks on save in CreateWidgetView , the Save method in WidgetService will be called and the widget will be saved. Now WidgetListViewModel needs to be notified about the appearance of a new widget!

A lengthy build leads to this question: how can I let WidgetListViewModel know that it needs to display a new widget?

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  • Update periodically, you have a ViewModel class that updates the list every X seconds, this is the only way to get updates without any notification mechanism that you have to manage.

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I agree that Cameron uses the WeakEvent template. I created a base class for ViewModel (in my example, I use the name PresentationModel) that supports the WeakEvent template.

You may find my sample project useful: http://www.codeplex.com/CompositeExtensions

Jbe

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Source: https://habr.com/ru/post/1704760/

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