如何从app.xaml访问当前视图模型

Question

When the program closes I want to save any changes to the data. I currently have a method to do so in my ViewModel . I have a OnExit method in the app.xaml file, but how can I access the save-method in the ViewModel from here?

App.xaml.cs

    protected override void OnExit(ExitEventArgs e)
    {
        //This is were I want to access the ViewModel

        base.OnExit(e);
    }

ViewModel.cs

    public void Save(){
        //This method save to the DB
    }

Answer 1

Consider using the Observer Pattern. Register your view-models as subscribers to an App's Close event. When the app's close event is triggered, notify your subscribers (ie view-models) so that they can react to that event.

• Prism provides an EventAggregator.

• Xamarin.Forms provides a MessagingCenter.

• Bizmonger provides a MessageBus.

You can use a mediator like the ones specified to manage a publisher / subscribe model without the classes knowing about each other.