how to change screen to a screen with kivymd bottomnavigation - python-3.x

Question

I added KivyMD BottomNavigation to my App, I am able to switch screens with icon, but the issue is switching back to a screen containing the BottomNavigation
(let's say we in any of the screens containing Toolbar and BottomNavigation, we use the toolbar to switch to a entirely different screen, I am unable to go back to the previous screen or even navigate to any of thr screens containing the bottomnavigation and toolbar, it returns a blank white screen).
Despite naming the screen, so my question is; 1. am I refering (naming) the BottomNavigationItem wrongly, if yes please what should I change. (2) is there something am missing, please let me know.
Thank you.
here's my main.py file
from kivymd.app import MDApp
from kivy.uix.screenmanager import Screen, ScreenManager, NoTransition
from kivy.core.window import Window
Window.size = (300, 530)
class MainScreen(Screen):
pass
class IntroScreen(Screen):
pass
class WaysScreen(Screen):
pass
class To_DoScreen(Screen):
pass
class SuccessScreen(Screen):
pass
class GoalsScreen(Screen):
pass
class BellaBaron(Screen):
pass
class SearchScreen(Screen):
pass
class MenuScreen(Screen):
pass
class CalendarScreen(Screen):
pass
class ExtraScreen(Screen):
pass
class ArchiveScreen(Screen):
pass
class Contact_InfoScreen(Screen):
pass
class TenThousandApp(MDApp):
def build(self):
self.theme_cls.primary_palette = 'Green'
self.theme_cls.primary_hue = '200'
# self.theme_cls.theme_style = 'Light'
self.sm = ScreenManager(transition=NoTransition())
self.sm.add_widget(MainScreen(name="main_screen"))
self.sm.add_widget(IntroScreen(name="intro_screen"))
self.sm.add_widget(WaysScreen(name="ways_screen"))
self.sm.add_widget(To_DoScreen(name="to_do_screen"))
self.sm.add_widget(SuccessScreen(name="success_screen"))
self.sm.add_widget(GoalsScreen(name="goals_screen"))
self.sm.add_widget(BellaBaron(name="bella_baron"))
self.sm.add_widget(SearchScreen(name="search_screen"))
self.sm.add_widget(MenuScreen(name="menu_screen"))
self.sm.add_widget(CalendarScreen(name="calendar_screen"))
self.sm.add_widget(ExtraScreen(name="extra_screen"))
self.sm.add_widget(ArchiveScreen(name="archive_screen"))
self.sm.add_widget(Contact_InfoScreen(name="contact_info_screen"))
return self.sm
def change_screen(self, screen):
self.sm.current = screen
TenThousandApp().run()
and here's my .kv file
# ScreenManager:
#start of imagelist
<MyTile#SmartTileWithLabel>
size_hint_y: None
height: "240dp"
<MainScreen>:
MDBottomNavigation:
# panel_color: .2, .2, .2, 1
MDBottomNavigationItem:
name: "intro_screen"
text: 'home'
icon: 'home'
MDBoxLayout:
orientation: 'vertical'
# md_bg_color: app.theme_cls.bg_dark
MDToolbar:
id: intro_screen_toolbar
title: '[font=Gabriola][size=40][color=#FD0101]First[/color][/size][size=28]project[/size][/font]'
right_action_items: [["calendar-month", lambda x: app.change_screen('to_do_screen')]] #links to to-do listss screen
elevation: "8dp"
MDCard:
orientation: 'vertical'
padding: 16
size_hint: None, None
size: "280dp", "360dp"
pos_hint: {"center_x": .5, "center_y": .6}
height: root.height - intro_screen_toolbar.height - dp(55)
y: root.height - intro_screen_toolbar.height - dp(50)
elevation: "8dp"
orientation: 'vertical'
radius: 15
ScrollView:
MDLabel:
markup: True
size_hint_y: None
size: self.texture_size
text:
"""[b][i]“Your time is limited, so don’t waste it living someone else’s life. Don’t be trapped by dogma – which is living with the results of other people’s thinking. Don’t let the noise of other’s opinions drown out your own inner voice. And most important, have the courage to follow your heart and intuition. They somehow already know what you truly want to become. Everything else is secondary.”[/i][/b]
– Steve Jobs"""
MDBottomNavigationItem:
name: "success_screen"
text: 'home'
icon: 'account-group'
BoxLayout:
orientation: 'vertical'
MDToolbar:
id: success_screen_toolbar
title: "Success Stories"
right_action_items: [["progress-clock", lambda x: app.change_screen('goals_screen')]] #links to goals and how screen
elevation: "8dp"
ScrollView:
MDGridLayout:
cols: 1
adaptive_height: True
padding: dp(4), dp(4)
spacing: dp(4)
MyTile:
source: "C:/Users/HP USER/Downloads/bella_baron.jpg"
text: "[size=26]Cat 1[/size]\\n[size=14]cat-1.jpg[/size]"
on_release:
app.root.current = 'bella_baron'
MyTile:
source: "C:/Users/HP USER/Downloads/bella_baron.jpg"
text: "[size=26]Cat 2[/size]\\n[size=14]cat-2.jpg[/size]"
tile_text_color: app.theme_cls.accent_color
MyTile:
source: "C:/Users/HP USER/Downloads/bella_baron.jpg"
text: "[size=26][color=#ffffff]Cat 3[/color][/size]\\n[size=14]cat-3.jpg[/size]"
tile_text_color: app.theme_cls.accent_color
MDBottomNavigationItem:
name: "search_screen"
text: 'search'
icon: 'magnify'
FloatLayout:
MDTextField:
mode: 'fill'
hint_text: "Search"
pos_hint: {"center_x": .5,"center_y": .9}
size_hint_x: None
width: 280
MDBottomNavigationItem:
name: "menu_screen"
text: 'menu'
icon: 'menu'
BoxLayout:
orientation: "vertical"
md_bg_color: (240/255, 240/255, 240/255, 1)
MDToolbar:
id: menu_screen_toolbar
title: "Tools"
elevation: "8dp"
MDCard:
orientation: 'vertical'
padding: 16
size_hint: None, None
size: "280dp", "360dp"
pos_hint: {"center_x": .5, "center_y": .6}
height: root.height - menu_screen_toolbar.height - dp(55)
y: root.height - menu_screen_toolbar.height - dp(50)
elevation: 8
orientation: 'vertical'
radius: 15
ScrollView:
MDList:
OneLineIconListItem:
text: "Calendar"
on_release:
app.root.current = "calendar_screen"
IconLeftWidget:
icon: "calendar-month"
OneLineIconListItem:
text: "Extra"
on_release:
app.root.current = "extra_screen"
IconLeftWidget:
icon: "notebook-multiple"
OneLineIconListItem:
text: "Archive"
on_release:
app.root.current = "archive_screen"
IconLeftWidget:
icon: "archive"
OneLineIconListItem:
text: "contact Us"
on_release:
app.root.current = "contact_info_screen"
IconLeftWidget:
icon: "email-mark-as-unread"
<WaysScreen>
name: "ways_screen"
BoxLayout:
orientation: 'vertical'
MDToolbar:
id: ways_screen_toolbar
title: "How-tos"
left_action_items: [['keyboard-backspace', lambda x: app.change_screen('intro_screen')]] # to add more list
left_action_items: [['keyboard-backspace', lambda x: app.change_screen('intro_screen')]]
elevation: "8dp"
ScrollView:
MDGridLayout:
cols: 1
adaptive_height: True
spacing: 10
padding: 10
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
Image:
source: "C:/Users/HP USER/Downloads/bella_baron.jpg"
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello dear'
ScrollView:
MDLabel:
size_hint_y: None
size: self.texture_size
# halign: 'center'
text:
"""This screens contains a MDcard which where the image is placed, and a MDLabel and neccessary widgets used to tell the success story, under the MDCard."""
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello boss'
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello goodness'
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello hi'
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello yes?'
<To_DoScreen>
name: "to_do_screen"
BoxLayout:
orientation: 'vertical'
MDToolbar:
id: to_do_screen_toolbar
title: 'To-Do-List'
right_action_items: [['plus', lambda x: x]] # to add more list
left_action_items: [['keyboard-backspace', lambda x: app.change_screen('intro_screen')]]
elevation: "8dp"
MDCard:
orientation: 'vertical'
padding: 16
elevation: 8
radius: 15
size_hint: None, None
size: '280', '360'
pos_hint: {"center_x": .5, "center_y": .6}
height: root.height - to_do_screen_toolbar.height + dp(10)
y: root.height - to_do_screen_toolbar.height - dp(20)
<GoalsScreen>
name: 'goals_screen'
BoxLayout:
orientation: 'vertical'
MDToolbar:
id: goals_screen_toolbar
title: 'Goals'
left_action_items: [['keyboard-backspace', lambda x: app.change_screen('success_screen')]]
elevation: "8dp"
MDCard:
orientation: 'vertical'
padding: 16
size_hint: None, None
size: "280dp", "360dp"
pos_hint: {"center_x": .5, "center_y": .6}
height: root.height - goals_screen_toolbar.height + dp(10)
y: root.height - goals_screen_toolbar.height - dp(20)
elevation: "8dp"
orientation: 'vertical'
radius: 15
<BellaBaron>
name: 'bella_baron'
BoxLayout:
orientation: 'vertical'
md_bg_color: (240/255, 240/255, 240/255, 1)
MDToolbar:
id: bella_baron_toolbar
title: "Bella Baron"
left_action_items: [["keyboard-backspace", lambda x: app.change_screen('success_screen')]]
right_action_items: [["progress-check", lambda x: app.change_screen('goals_screen')]] #link to progress screen
elevation: "8dp"
ScrollView:
MDGridLayout:
cols: 1
adaptive_height: True
spacing: 10
padding: 10
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
Image:
source: "C:/Users/HP USER/Downloads/bella_baron.jpg"
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello dear'
ScrollView:
MDLabel:
size_hint_y: None
size: self.texture_size
# halign: 'center'
text:
"""This screens contains a MDcard which where the image is placed, and a MDLabel and neccessary widgets used to tell the success story, under the MDCard."""
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello boss'
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello goodness'
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello hi'
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello yes?'
<CalendarScreen>
name: "calendar_screen"
BoxLayout:
orientation: 'vertical'
MDToolbar:
id: calendar_screen_toolbar
title: 'Calendar'
left_action_items: [['keyboard-backspace', lambda x: app.change_screen('menu_screen')]]
right_action_items: [['calendar', lambda x: x]] # on press returns today's date
elevation: "8dp"
MDCard:
orientation: 'vertical'
padding: 16
elevation: 8
radius: 15
size_hint: None, None
size: '280', '360'
pos_hint: {"center_x": .5, "center_y": .6}
height: root.height - calendar_screen_toolbar.height + dp(10)
y: root.height - calendar_screen_toolbar.height - dp(20)
# I will remove this screen if there is no need for it.
<ExtraScreen>
name: "extra_screen"
BoxLayout:
orientation: 'vertical'
MDToolbar:
id: extra_screen_toolbar
title: 'Extra'
left_action_items: [['keyboard-backspace', lambda x: app.change_screen('menu_screen')]]
elevation: "8dp"
ScrollView:
MDGridLayout:
cols: 1
adaptive_height: True
spacing: 10
padding: 10
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
Image:
source: "C:/Users/HP USER/Downloads/bella_baron.jpg"
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello dear'
ScrollView:
MDLabel:
size_hint_y: None
size: self.texture_size
# halign: 'center'
text:
"""This screens contains a MDcard which where the image is placed, and a MDLabel and neccessary widgets used to tell the success story, under the MDCard."""
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello boss'
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello goodness'
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello hi'
MDCard:
size_hint: None, None
size: "280dp", "130dp"
radius: 15
caption: 'Hello yes?'
<ArchiveScreen>
name: "archive_screen"
BoxLayout:
orientation: 'vertical'
MDToolbar:
id: archive_screen_toolbar
title: 'Archive'
left_action_items: [['keyboard-backspace', lambda x: app.change_screen('menu_screen')]]
elevation: "8dp"
MDCard:
orientation: 'vertical'
padding: 16
elevation: 8
radius: 15
size_hint: None, None
size: '280', '360'
pos_hint: {"center_x": .5, "center_y": .6}
height: root.height - archive_screen_toolbar.height + dp(10)
y: root.height - archive_screen_toolbar.height - dp(20)
<Contact_InfoScreen>
name: "contact_info_screen"
BoxLayout:
orientation: 'vertical'
MDToolbar:
id: contact_info_screen_toolbar
title: 'Contact Info'
left_action_items: [['keyboard-backspace', lambda x: app.change_screen('menu_screen')]]
elevation: "8dp"
MDCard:
orientation: 'vertical'
padding: 16
elevation: 8
radius: 15
size_hint: None, None
size: '280', '360'
pos_hint: {"center_x": .5, "center_y": .6}
height: root.height - contact_info_screen_toolbar.height + dp(10)
y: root.height - contact_info_screen_toolbar.height - dp(20)
ScrollView:
MDLabel:
size_hint_y: None
size: self.texture_size
text:
"""feel free to reach us #"""

Answer 1

To change to a different MDBottomNavigationItem in a MDBottomNavigation, you should use the switch_tab() method of MDBottomNavigation. You can add a method to your TenThousandApp class:
def change_screen_item(self, nav_item):
# change to the MainScreen and switch to the spcified MDBottomNavigationItem
s = self.sm.get_screen('main_screen')
s.ids.bottom_nav.switch_tab(nav_item)
self.sm.current = 'main_screen'
In your kv, you must add an id for the MDBottomNavigation:
<MainScreen>:
MDBottomNavigation:
id: bottom_nav
# panel_color: .2, .2, .2, 1
That id is used to access the MDBottomNavigation instance.
Then in the kv, you can use the change_screen_item() to switch to the MainScreen and switch to the specified MDBottomNavigationItem, like this:
<CalendarScreen>
name: "calendar_screen"
BoxLayout:
orientation: 'vertical'
MDToolbar:
id: calendar_screen_toolbar
title: 'Calendar'
left_action_items: [['keyboard-backspace', lambda x: app.change_screen_item('intro_screen')]]
right_action_items: [['calendar', lambda x: x]] # on press returns today's date
elevation: "8dp"
The above code will switch to the intro_screen item of the MainScreen.