How to clear LiveData stored value?

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暖寄归人
暖寄归人 2021-01-30 02:34

According to LiveData documentation:

The LiveData class provides the following advantages:

...

Always up to date data: If a Li

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  • 2021-01-30 03:07

    I`m not sure if it will work in your case, but in my case (increasing/decreasing items amount in Room by click on views) removing Observer and checking if there is active observers let me do the job:

    LiveData<MenuItem> menuitem = mViewModel.getMenuItemById(menuid);
    menuitem.observe(this, (MenuItem menuItemRoom) ->{
                    menuitem.removeObservers(this);
                    if(menuitem.hasObservers())return;
    
                    // Do your single job here
    
                    });
    });  
    

    UPDATE 20/03/2019:

    Now i prefer 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<>();
    
     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();
              }
            });
    
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