In MVVMCross, is it possible to close a viewmodel and pass values back to the previous viewmodel in the navigation stack?

Question

Consider the following example. I have three view models, ViewModel_A, ViewModel_B, and ViewModel_Values.

I want to be able to navigate to ViewModel_Values from either ViewModel_A or ViewModel_B, select a value from ViewModel_Values, then return that value to the calling view model.

Is there a way of passing arguments to previous view models in the navigation stack so that I can simply call ViewModel_Values.Close(this), thereby ensuring that the ViewModels_Values is decoupled from any other view models and can be used with arbitrary "parent" view models?

Answer 1

Installing & using the MvxMessenger plugin is a great way to decouple view model communication in MvvmCross -

In your case, you could set up a new message -

public class ValuesChangedMessage : MvxMessage
{      
    public ValuesChangedMessage(object sender, int valuea, string valueb)
        : base(sender)
    {
        Valuea = valuea;
        Valueb = valueb;        
    }

    public int Valuea { get; private set; }
    public string Valueb { get; private set; }
}

In ViewModel_Values, you would act on / publish your UX changes with -

_mvxMessenger.Publish<ValuesChangedMessage>(new ValuesChangedMessage(this, 1, "boo!"));

And in ViewModel_A, ViewModel_B you would subscribe and act on them (as your ViewModel A / B would be still in the navigation stack when you pushed ViewModel_Values from them, so they could receive the message) -

private MvxSubscriptionToken _messageToken;              

_messageToken = _mvxMessenger.Subscribe<ValuesChangedMessage>(async message =>
        {
            // use message.Valuea etc ..
        });

More infos here -

https://www.mvvmcross.com/documentation/plugins/messenger?scroll=644 https://www.youtube.com/watch?feature=player_embedded&v=HQdvrWWzkIk