Viewmodel’s communication: return data to previous screen

Question

I have a screen A that has a text field and a button, that screen button A, opens a second screen B.

That screen B has another text field to fill and save, when the person click save the screen closes, and what she filled on the screen B must appear filled in the screen field A.

I used canvas A and B as an example, how to do using MVVM ?

I found this question, but what I want to do is the opposite of MVVM.

Answer 1

One possibility is to use the Event Aggregator Pattern.

Write a class for the event:

public class TelaBResultEvent : PubSubEvent<string>{}

In the Viewmodel maker of the screen A subscribe the event:

eventAggregator.GetEvent<TelaBResultEvent>().Subscribe(OnTelaBResult);

• eventAggregator is a IEventAggregator injected into the manufacturer.

• OnTelaBResult is a Viewmodel method with signature

  public void OnTelaBResult(string telaBResult)
  

  that will be called when the event is received.
  Use the value received in the parameter telaBResult in the text field.

In Viewmodel of screen B publish the event when save/close the screen, passed the value of the text field.

_eventAggregator.GetEvent<TelaBResultEvent>().Publish("Texto a publicar");

• _eventAggregator is a field/property to which a IEventAggregator injected into the Viewmodel constructor.