GWT Asynchronous callback and UI

Hello all,

      I have a Composite with Widgets that are populated from the database.  Let's assume I need to add new Item object and ID for this object comes from database after object is persisted on the server. So I did:

     

private void addItem(String title, String description) {
          ItemDTO itemDto = new ItemDTO(0L, title, description, false);
          todoService.saveItem(itemDto, new AsyncCallback<ItemDTO>() {
            @Override
            public void onFailure(Throwable caught) {
                Window.alert("Failed to save item");
            }
            @Override
            public void onSuccess(ItemDTO itemDto) {
                Window.alert("Item saved");
                item.setId(itemDto.getId());
                item.setTitle(itemDto.getTitle());
                item.setDescription(itemDto.getDescription());
                content.add(item);
            }
           
        });

      
       This way Item is added to database, but Window.alert is not shown and UI does not show the item newly added.
       If I did this way:
 

private void addItem(String title, String description) {
        Item item = new Item();
        item.setTitle(title);
        item.setDescription(description);
        content.add(item);
        ItemDTO itemDto = new ItemDTO(0L, title, description, false);
        todoService.saveItem(itemDto, new AsyncCallback<Long>() {
            @Override
            public void onFailure(Throwable caught) {
                Window.alert("Failed to save item");
            }

            @Override
            public void onSuccess(Long id) {
                Window.alert("Item saved");
                updateItem(id);
            }

        });
    }

    private void updateItem(Long id) {
        Item item = (Item) content.getWidget(content.getWidgetCount()-1);
        item.setId(id);
    }

         Everything works as expected, but "update" item logic is a bit dangerous. Why I can't add item object in callback?  What's wrong with a first example?

Thank you.

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