android - LiveData prevent receive the last value when start observing

Question

Is it possible to prevent LiveData receive the last value when start observing? I am considering to use LiveData as events.

For example events like show message, a navigation event or a dialog trigger, similar to EventBus.

The problem related to communication between ViewModel and fragment, Google gave us LiveData to update the view with data, but this type of communication not suitable when we need update the view only once with single event, also we cannot hold view's reference in ViewModel and call some methods because it will create memory leak.

I found something similar SingleLiveEvent - but it work only for 1 observer and not for multiple observers.

--- Update ----

As @EpicPandaForce said "There is no reason to use LiveData as something that it is not", probably the intent of the question was Communication between view and ViewModel in MVVM with LiveData

Answer 1

I`m using this EventWraper class from Google Samples inside MutableLiveData

/**
 * Used as a wrapper for data that is exposed via a LiveData that represents an event.
 */
public class Event<T> {

    private T mContent;

    private boolean hasBeenHandled = false;


    public Event( T content) {
        if (content == null) {
            throw new IllegalArgumentException("null values in Event are not allowed.");
        }
        mContent = content;
    }
    
    @Nullable
    public T getContentIfNotHandled() {
        if (hasBeenHandled) {
            return null;
        } else {
            hasBeenHandled = true;
            return mContent;
        }
    }
    
    public boolean hasBeenHandled() {
        return hasBeenHandled;
    }
}

In ViewModel :

 /** expose Save LiveData Event */
 public void newSaveEvent() {
    saveEvent.setValue(new Event<>(true));
 }

 private final MutableLiveData<Event<Boolean>> saveEvent = new MutableLiveData<>();

 public LiveData<Event<Boolean>> onSaveEvent() {
    return saveEvent;
 }

In Activity/Fragment

mViewModel
    .onSaveEvent()
    .observe(
        getViewLifecycleOwner(),
        booleanEvent -> {
          if (booleanEvent != null)
            final Boolean shouldSave = booleanEvent.getContentIfNotHandled();
            if (shouldSave != null && shouldSave) saveData();
          }
        });