Kivy: RecycleView not updating - kivy

Question

I have two screens in my Kivy-based app, each with a RecycleView to display lists. Both RVs should update when I press a button (add_button_clicked()) on one screen. Currently, the first RV (AddRecipe screen) works mostly as intended. However, the RV on the ViewList screen does not update with new data.
I am new to Python and even newer to Kivy - what am I missing here?
.py:
#! python3
# GroceryList.py
import kivy
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.gridlayout import GridLayout
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.widget import Widget
from kivy.uix.label import Label
from kivy.uix.button import Button
from kivy.uix.spinner import Spinner
from kivy.properties import ListProperty
from kivy.properties import ObjectProperty
from kivy.uix.recycleview import RecycleView
selectedMeals = []
ingredients = []
class ViewList(Screen):
def updateList(self, portions, recipe):
ingredients.append((portions, recipe))
print(ingredients) # This proves updateList is getting called
##THE FOLLOW RV THINGS DON'T WORK:
self.ids.shoplist.data = [{'text': '%s (%s)' %(ingredients[i][0], ingredients[i][1])}
for i in range(len(ingredients))]
self.ids.shoplist.refresh_from_data()
##
class AddRecipe(Screen):
recipes = ListProperty()
recipes = {'Guacarole':5, 'Salsa':3, 'Chips':1} # Sample dict for demo
def add_one(self):
if self.addportions.text != '':
value = int(self.addportions.text)
self.addportions.text = str(value+1)
def subtract_one(self):
if self.addportions.text != '':
value = int(self.addportions.text)
self.addportions.text = str(value-1)
def add_button_clicked(self, recipe, portions):
if recipe != '':
selectedMeals.append((recipe, portions))
self.ids.mealslist.data = [{'text': '%s (%s)' %(selectedMeals[i][0], selectedMeals[i][1])}
for i in range(len(selectedMeals))]
self.ids.mealslist.refresh_from_data()
ViewList().updateList(portions, recipe)
def spinner_clicked(self, val):
self.addportions.text = str(self.recipes[val])
class WindowManager(ScreenManager):
pass
class GroceryList(App):
mealsRVdata = ListProperty()
shoppingRVdata = ListProperty()
def __init__(self, **kwargs):
super().__init__(**kwargs)
self.sm = ScreenManager()
def build(self):
Builder.load_file("grocerylist.kv")
screens = [ViewList(name='viewlist'), AddRecipe(name='addrecipe')]
for screen in screens:
self.sm.add_widget(screen)
self.sm.current = "addrecipe"
return self.sm
if __name__ == '__main__':
GroceryList().run()
And .kv:
#:kivy 1.11.1
# GroceryList.kv
# Used by GroceryList.py
WindowManager:
AddRecipe:
ViewList:
<ViewList>:
name: "viewlist"
shoplist: shoplist
BoxLayout:
orientation: 'vertical'
BoxLayout:
size_hint: (1, 0.8)
RecycleView:
id: shoplist
data: app.shoppingRVdata
viewclass: 'RVLabel'
RecycleGridLayout:
cols: 1
size_hint: None, None
default_size: sp(200), sp(25)
height: self.minimum_height
width: self.minimum_width
BoxLayout:
size_hint: (1, 0.2)
Button:
text: "View shopping list"
on_release:
app.root.current = "viewlist"
Button:
text: "Add recipes"
on_release:
app.root.current = "addrecipe"
root.manager.transition.direction = "left"
<AddRecipe>:
name: "addrecipe"
addportions: addportions
mealslist: mealslist
BoxLayout:
orientation: 'vertical'
BoxLayout:
size_hint: (1, 0.08)
Label:
size_hint: (0.64, 1)
font_size: 20
text: "Select a meal to add"
Label:
size_hint: (0.36, 1)
font_size: 20
text: "Select portions"
BoxLayout:
size_hint: (1, 0.08)
Spinner:
id: add_spinner
size_hint: (0.64, 1)
text: ""
values: root.recipes.keys()
on_text:
root.spinner_clicked(add_spinner.text)
Button:
size_hint: (0.12, 1)
font_size: 36
text: "-"
on_release: root.subtract_one()
Label:
id: addportions
size_hint: (0.12, 1)
font_size: 24
text: ''
Button:
size_hint: (0.12, 1)
font_size: 36
text: "+"
on_release: root.add_one()
FloatLayout:
size_hint: (1, 0.08)
Button:
size_hint: (0.4, 1)
pos_hint: {"x": 0.3, "top": 1}
text: "Add to shopping list"
on_release:
root.add_button_clicked(add_spinner.text, addportions.text)
BoxLayout:
size_hint: (1, 0.68)
RecycleView:
id: mealslist
data: app.mealsRVdata
viewclass: 'RVLabel'
RecycleGridLayout:
cols: 1
size_hint: None, None
default_size: sp(200), sp(25)
height: self.minimum_height
width: self.minimum_width
BoxLayout:
size_hint: (1, 0.08)
Button:
text: "View shopping list"
on_release:
app.root.current = "viewlist"
root.manager.transition.direction = "right"
Button:
text: "Add recipes"
on_release:
app.root.current = "addrecipe"
<RVLabel#Label>:
text_size: self.size

Answer 1

I stumbled across the fix while browsing other questions - specify the RV more fully:
App.get_running_app().root.get_screen('viewlist').ids.shoplist.data = ....
I'm going to leave the question up, though, because now I want to know why this RV needs to be specified so completely, while the one in the AddRecipe screen doesn't.