Develop Reference

Adaptive_width property of MDLabel is not working correctly

I am making an app using kivy & kivymd and in one part of it, I would like the labels to take as much space as the actual text.
This seems pretty straightforward with kivy itself but for some reason, nothing works with the MDLabel class. I tried setting the adaptive_width property to True and I also tried to directly set the width to the texture_size[0] property but none of them worked (and yes I installed kivymd directly from github).
Here is my code:
from kivy.lang import Builder
from kivymd.app import MDApp
class MainApp(MDApp):
def __init__(self, **kwargs):
super(MainApp, self).__init__(**kwargs)
self.kv = Builder.load_string('''
#:kivy 2.0.0
BoxLayout:
MDLabel:
text: "Supposedly adaptive width (KivyMD)"
font_size: "21sp"
halign: "center"
adaptive_width: True
# I also tried directly setting the width to the texture_size but the results were worse
# size_hint_x: None
# width: self.texture_size[0]
canvas.before:
Color:
rgba: .8, .1, .2, .5
Rectangle:
pos: self.pos
size: self.size
Widget:
MDSeparator:
orientation: "vertical"
Widget:
Label:
text: "Actual adaptive width (Standard Kivy)"
font_size: "21sp"
color: 0, 0, 0, 1
size_hint_x: None
width: self.texture_size[0]
canvas.before:
Color:
rgba: 0, .6, .2, .5
Rectangle:
pos: self.pos
size: self.size
''')
def build(self):
return self.kv
if __name__ == '__main__':
MainApp().run()
Here is my results:

I don't believe that MDLabel supports the adaptive_width property. In using the width: self.texture_size[0], it seems that you must also add the text_size: None, None to the MDLabel, and it seems that its location in the kv is important. Here is a version of part of your kv that seems to work:
BoxLayout:
MDLabel:
text: "Supposedly adaptive width (KivyMD)"
font_size: "21sp"
halign: "center"
# adaptive_width: True
# I also tried directly setting the width to the texture_size but the results were worse
size_hint_x: None
width: self.texture_size[0]
text_size: None, None # added, and must be in this location
canvas.before:
Color:
rgba: .8, .1, .2, .5
Rectangle:
pos: self.pos
size: self.size

How to change label background color dynamically in Kivy

I try to make a simple ToDoList program.There are add, remove and do it buttons. But I have some bugs about labels color. When I click "DO IT" button label color change in scrollview but when I click remove button when some of them done, colored labels change. I did using canvas. How can I fix this problem?
class Home(Screen):
def __init__(self,**kwargs):
super(Home,self).__init__(**kwargs)
def addWidget(self):
task_input = self.ids.task_input.text
newListItem = EachTask(text=task_input ,
id=str((len(self.ids.add_field.children))) )
print(newListItem.id)
self.ids.add_field.add_widget(newListItem)
class EachTask(BoxLayout):
def __init__(self, text= "", **kwargs):
super(EachTask,self).__init__(**kwargs)
self.ids.label.text = text
def Do_Task(self,instance):
child = instance.parent.parent
with self.canvas.before:
Color(.5,1,.2,1, mode='rgba')
Rectangle(pos=child.ids.label.pos, size=child.ids.label.size)
kv_file
<FlatButton#ButtonBehavior+Label>:
font_size: 15
<Home>:
BoxLayout:
id: home
orientation: "vertical"
spacing: 5
#space_x: self.size[0]/2
canvas.before:
Color:
rgba: (1,1,1,1)
Rectangle:
size: self.size
pos: self.pos
##########HEADER#######
BoxLayout:
id: header
size_hint_y: None
height: 50
canvas.before:
Color:
rgba: (.85,.7,.2,1)
Rectangle:
size: self.size
pos: self.pos
Label:
text: "TO DO LIST"
font_size: "20sp"
bold: True
size_hint_x: .9
FlatButton:
text: "Back"
size_hint_x: .1
####################################
ScrollView:
canvas.before:
Color:
rgba: (1,1,.2,.2)
Rectangle:
size: self.size
pos: self.pos
BoxLayout:
id: add_field
size_hint_y: None
height: self.minimum_height
orientation: 'vertical'
spacing: 2 #Spaces between childs
#####################################################
BoxLayout:
id: input_field
size_hint_y: None
height: 80
TextInput:
id: task_input
focus: True
size_hint_x: .9
multiline: False
Button:
font_size: "40sp"
size_hint_x: .1
text: "+"
on_release: root.addWidget()
id: button1
color: 1,0.5,0.5,1
#######################################################
<EachTask>:
size_hint_y: None
height: 50
id: each_task
BoxLayout:
Label:
size_hint_x: .8
id: label
canvas.before:
Color:
rgba: (1,.2,.2,.2)
Rectangle:
size: self.size
pos: self.pos
Button:
size_hint_x: .1
text: "X"
on_release: app.root.ids.add_field.remove_widget(root)
Button:
size_hint_x: .1
text: "DO IT"
on_release: root.Do_Task(self)

The following enhancements are required to the kv and py files to solve the problem.
Method 1 - Kivy automatically created & added an ObjectProperty, rgba
Kivy automatically created & added an ObjectProperty
If the widget doesn’t have a property with the given name, an
ObjectProperty will be automatically created and added to the widget.
kv file
Add a class attribute, rgba and initialize it to default colour, (1, .2, .2, .2) to class rule, <EachTask>:
Replace label's colour to root.rgba
Snippets - kv file
<EachTask>:
rgba: (1,.2,.2,.2) # Kivy auto created & added ObjectProperty, "rgba"
...
BoxLayout:
Label:
size_hint_x: .8
id: label
canvas.before:
Color:
rgba: root.rgba
...
py file
Remove all the codes in method Do_Task()
Add self.rgba = [.5, 1, .2, 1] whereby self refers to the current widget i.e. EachTask object.
Snippets - py file
def Do_Task(self, instance):
self.rgba = [.5, 1, .2, 1]
Method 2 - Explicitly declaring rgba
kv file
Replace rgba: (1,.2,.2,.2) with root.rgba
Snippets - kv file
<EachTask>:
...
BoxLayout:
Label:
size_hint_x: .8
id: label
canvas.before:
Color:
rgba: root.rgba
...
py file
Add import statement, from kivy.properties import ListProperty
Declare class attribute, rgba of ListProperty type and initilaize it to default colour, [1, .2, .2, .2] in class EachTask()
Remove all the codes in method Do_Task()
Add self.rgba = [.5, 1, .2, 1] whereby self refers to the current widget i.e. EachTask object.
Snippets - py file
from kivy.properties import ListProperty
...
class EachTask(BoxLayout):
rgba = ListProperty([1, .2, .2, .2])
...
def Do_Task(self, instance):
self.rgba = [.5, 1, .2, 1]

button and label text not showing

the two windows in the picture are exact copies(same line of code), only difference being that the right window is a screen inside a screen manager, but somehow the window on the right does not show the texts.
i'm not sure what the problem is and can't find anything related to it while doing research.
RIGHT WINDOW PYTHON FILE:
import kivy
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.config import Config
space = ""
x = [(a * 9), (a*16)]
Config.set('graphics', 'width', x[0])
Config.set('graphics', 'height', x[1])
class MainScreen(Screen):
pass
class SecondScreen(Screen):
pass
class ThirdScreen(Screen):
pass
kv = Builder.load_file("main2.kv")
class ComplimentUI(App):
def build(self):
return kv
def change_screen(self, x):
scrnmanager = self.root.ids['sm']
scrnmanager.current = x
if __name__ == "__main__":
ComplimentUI().run()
RIGHT WINDOW BUILDER FILE:(main2.kv)
#:include secondscreen.kv
#:include thirdscreen.kv
<MainScreen>:
canvas.before:
Color:
rgb: .59, .74, .20
Rectangle:
size: self.size
pos: self.pos
FloatLayout:
TextInput:
pos_hint: {'center_x':1, 'top':.1}
size_hint: .1,.1
multiline: False
font_size: 20
font_name: "Dimbo Regular"
background_normal: ''
background_color: 0,0,0,0
Button:
text: "PLAY!"
pos_hint: {'center_x':.5, 'center_y':.3}
size_hint: .8, .17
font_name: "Splatch"
color: 0.15, .5, 0.2, 1
font_size: 0.14 * self.width
background_normal: ''
background_color: 0,0,0,0
on_press:
print("pressed, navigating to prev screen")
app.change_screen("screentwo")
root.manager.transition.direction = "left"
canvas.before:
Color:
rgb: 1,1, .8,1
RoundedRectangle:
size: self.size
pos: self.pos
radius: [4,]
ScreenManager:
GridLayout:
cols: 1
ScreenManager:
id: sm
MainScreen:
name: "screenone"
id: screenone
SecondScreen:
name: "screentwo"
id: screentwo
ThirdScreen:
name: "thirdscreen"
id: thirdscreen[enter image description here][1]
LEFT WINDOW PYTHON FILE:
import kivy
from kivy.app import App
from kivy.lang import Builder
from kivy.config import Config
space = "";
x = [(a * 9), (a*16)]
Config.set('graphics', 'width', x[0])
Config.set('graphics', 'height', x[1])
kv = Builder.load_file("main.kv")
class MyMainApp(App):
def build(self):
return kv
if __name__ == "__main__":
MyMainApp().run()
LEFT WINDOW BUILDER FILE:(main.kv)
FloatLayout:
canvas.before:
Color:
rgb: .59, .74, .20
Rectangle:
size: self.size
pos: self.pos
TextInput:
pos_hint: {'center_x':1, 'top':.1}
size_hint: .1,.1
multiline: False
font_size: 20
font_name: "Dimbo Regular"
background_normal: ''
background_color: 0,0,0,0
Button:
text: "PLAY!"
pos_hint: {'center_x':.5, 'center_y':.3}
size_hint: .8, .17
font_name: "Splatch"
color: 0.15, .5, 0.2, 1
font_size: 0.14 * self.width
background_normal: ''
background_color: 0,0,0,0
on_press:
print("pressed, navigating to prev screen")
app.change_screen("screentwo")
root.manager.transition.direction = "left"
canvas.before:
Color:
rgb: 1,1, .8,1
RoundedRectangle:
size: self.size
pos: self.pos
radius: [4,]
NEW EDIT:
as i pointed out in the comment below, the same problem happens with the FloatLayout of secondscreen.kv and thirdscreen.kv, if i put it inside the builder file of the left window, its normal. But when i put it inside a screen inside a screen manager(like the right window) it's gone. the same problem happens to all my screens. the reason i only put the mainscreen.kv is because its the shortest out of all the screens, but nonetheless i will still provide the files, but only 1 version of it (the one used for the right window) since they're basically the same lines. (only difference being the added first line for its class name and a slight indetation change to fit the levels)
SECONDSCREEN BUILDER FILE:
<SecondScreen>:
FloatLayout:
canvas.before:
Color:
rgb: .59, .74, .20
Rectangle:
size: self.size
pos: self.pos
TextInput:
pos_hint: {'center_x':.5, 'center_y':.56}
size_hint: .8, .3
multiline: False
font_size: 20
font_name: "Dimbo Regular"
background_normal: ''
background_color: 1, 1, .8, 1
Label:
pos_hint: {'center_x':.5, 'center_y':.76}
size_hint: .8, .07
text: "NAME!"
font_size: 0.8 * self.height
font_name: "kidsrock"
color: 0.15, .5, 0.2, 1
background_color: 0,0,0,0
canvas.before:
Color:
rgb: 1,1, .8,1
RoundedRectangle:
size: self.size
pos: self.pos
radius: [4,]
Button:
text: "<<<"
size_hint: .28, .07
pos_hint: {'center_x':.24, 'center_y':.1}
font_name: "kidsrock"
color: 0.15, .5, 0.2, 1
font_size: 0.35 * self.width
background_normal: ''
background_color: 0,0,0,0
on_press:
print("pressed, navigating to prev screen")
app.change_screen("screenone")
root.manager.transition.direction = "right"
canvas.before:
Color:
rgb: 1,1, .8,1
RoundedRectangle:
size: self.size
pos: self.pos
radius: [4,]
Button:
pos_hint: {'center_x':.8, 'center_y':.35}
size_hint: .2, .07
background_normal: ''
background_color: 0,0,0,0
color: 0.15, .5, 0.2, 1
text: "ENTER"
font_name: "kidsrock"
font_size: 0.25 * self.width
on_press:
print("pressed, navigating to next screen")
app.change_screen("thirdscreen")
root.manager.transition.direction = "left"
canvas.before:
Color:
rgb: 1,1, .8,1
RoundedRectangle:
size: self.size
pos: self.pos
radius: [4,]
THIRDSCREEN BUILDER FILE:
<ThirdScreen>:
FloatLayout:
canvas.before:
Color:
rgb: .59, .74, .20
Rectangle:
size: self.size
pos: self.pos
TextInput:
pos_hint: {'center_x':1, 'top':.1}
size_hint: .1, .1
multiline: False
font_size: 20
font_name: "Dimbo Regular"
background_normal: ''
background_color: 0, 0, 0, 0
Label:
pos_hint: {'center_x':.5, 'center_y':.71}
size_hint: .8, .17
text: "COMPLIMENT!"
font_size: 20
font_name: "kidsrock"
color: 0.15, .5, 0.2, 1
background_color: 0,0,0,0
canvas.before:
Color:
rgb: 1,1, .8,1
RoundedRectangle:
size: self.size
pos: self.pos
radius: [4,]
Button:
pos_hint: {'center_x':.24, 'center_y':.1}
size_hint: .28, .07
font_name: "kidsrock"
color: 0.15, .5, 0.2, 1
font_size: 0.35 * self.width
text: "<<<"
background_normal: ''
background_color: 0,0,0,0
on_press:
print("pressed, navigating to prev screen")
app.change_screen("screentwo")
root.manager.transition.direction = "right"
canvas.before:
Color:
rgb: 1,1, .8,1
RoundedRectangle:
size: self.size
pos: self.pos
radius: [4,]
NEW- NEW EDIT!:
UPDATE
after restarting my computer, it now looks like this.

Root Cause - Button & Label text not showing
The most probable cause is that the default color for text is white ([1, 1, 1, 1]), and the background color for both widgets are also white. You need to set the text color to non-white e.g. black ([0, 0, 0, 1]).
TextInput Box - not showing
The TexInput box is not visible in both windows (left & right) because of background_normal: '' and background_color: 0,0,0,0.
Comment them off and the TextInput box will be visible.
Button's text, 'PLAY' - not showing in right window
It could be something in the include kv files e.g. secondscreen.kv, and/or thirdscreen.kv that are/is causing the visibility. Comment off both kv files to trouble shoot the problem.
Example
The following example of the right window i.e. using ScreenManager is able to display the Button's text, "PLAY" and also the TextInput box.
main-right.py
from kivy.app import App
from kivy.uix.screenmanager import Screen
from kivy.lang import Builder
class MainScreen(Screen):
pass
class SecondScreen(Screen):
pass
class ThirdScreen(Screen):
pass
kv = Builder.load_string("""
# :include secondscreen.kv
# :include thirdscreen.kv
<MainScreen>:
canvas.before:
Color:
rgb: .59, .74, .20
Rectangle:
size: self.size
pos: self.pos
FloatLayout:
TextInput:
hint_text: 'Type here'
pos_hint: {'center_x':1, 'top':.1}
size_hint: .1,.1
multiline: False
font_size: 20
# font_name: "Dimbo Regular"
# background_normal: ''
# background_color: 0,0,0,0
Button:
text: "PLAY!"
pos_hint: {'center_x':.5, 'center_y':.3}
size_hint: .8, .17
#font_name: "Splatch"
color: 0.15, .5, 0.2, 1
font_size: 0.14 * self.width
background_normal: ''
background_color: 0,0,0,0
on_press:
print("pressed, navigating to prev screen")
app.change_screen("screentwo")
root.manager.transition.direction = "left"
canvas.before:
Color:
rgba: 1, 1, .8, 1
RoundedRectangle:
size: self.size
pos: self.pos
radius: [4,]
GridLayout:
cols: 1
ScreenManager:
id: sm
MainScreen:
name: "screenone"
id: screenone
SecondScreen:
name: "screentwo"
id: screentwo
ThirdScreen:
name: "thirdscreen"
id: thirdscreen
""")
class RightWindow(App):
title = "ComplimentUI"
def build(self):
return kv
if __name__ == "__main__":
RightWindow().run()
Output

I was facing a similar problem and the bug for me turned out to be a declaration of size_hint_x for the button. Once I removed that, the text was visible.

Why is Screens not loading in Kv Language?

I have an App with three toggle buttons in a fixed header that is an outside indented layout for screen manager. On initialisation, the Import screen must show i.e. self.ids.scrn_man.current = 'import_scn" and when a toggle button is pushed a next screen should show i.e. on_state: scrn_man.current = "settings_scrn".
But for some reason, only the header is showing and the screens do not want to transition. I don't get any errors.
I tried different layouts as my Apps main class inheritance including, FloatLayout, StackLayout and BoxLayout. I also made the header fixed with AnchorLayout and use a different layout as the inline layout for ScreenManager. If I remove the ScreenManager I see my widgets, but of course, I cannot transition. I did at first try using TabbedPanel to house my different widgets but I encountered a constant RefError: weak object reference if I added too many widgets (but that's not for now). So I re-designed with something I knew worked on a previous App albeit less complex.
Here is my faulty code:
from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.stacklayout import StackLayout
from kivy.uix.togglebutton import ToggleButton
from kivy.lang import Builder
from kivy.uix.popup import Popup
from kivy.properties import StringProperty, ObjectProperty
Builder.load_string("""
<RoundedButton#Button>:
background_color: 0,0,0,0
canvas.before:
Color:
rgba: (.47,.47,.47,1) if self.state=='normal' else (1,.6,0,1)
RoundedRectangle:
pos: self.pos
size: self.size
radius: [8,]
<RoundedCancelButton#Button>:
background_color: 0,0,0,0
canvas.before:
Color:
rgba: (.47,.47,.47,1) if self.state=='normal' else (1,.2,.2,1)
RoundedRectangle:
pos: self.pos
size: self.size
radius: [8,]
<RoundedAcceptButton#Button>:
background_color: 0,0,0,0
canvas.before:
Color:
rgba: (.47,.47,.47,1) if self.state=='normal' else (.2,1,.6,1)
RoundedRectangle:
pos: self.pos
size: self.size
radius: [8,]
<TabbedContainer#ToggleButton>:
background_color: (1, .5, 0, 1)
background_normal: ''
size_hint_y: None
height: 50
size_hint_x: (1 / 3)
spacing: 30
<Tab>:
canvas.before:
Color:
rgba: (.89, .89, .89, 1)
Rectangle:
size: self.size
pos: self.pos
orientation: 'lr-tb'
BoxLayout:
orientation: 'horizontal'
size_hint_y: None
height: 30
canvas.before:
Color:
rgba: (1, .3, 0, 1)
Rectangle:
size: self.size
pos: self.pos
Label:
text: 'Test'
color: (1, 1, 1, 1)
size_hint_x: 1
StackLayout:
orientation: 'lr-tb'
Label:
text: ''
size_hint_x: 1
size_hint_y: None
height: 10
TabbedContainer:
id: import_tog
text: 'Import'
state: 'down'
group: 'admin_navs'
on_state: root.change_screen(self)
TabbedContainer:
id: calculate_tog
text: 'Calculate'
group: 'admin_navs'
on_state: root.change_screen(self)
TabbedContainer:
id: settings_tog
text: 'Settings'
group: 'admin_navs'
on_state: root.change_screen(self)
BoxLayout:
id: ui_content
padding: 10
ScreenManager: #Problem here I think
id: scrn_man
Screen:
id: import_scrn
name: 'import_scrn'
StackLayout:
orientation: 'lr-tb'
Label:
text: ''
size_hint_x: 1
Label:
text: ''
size_hint_x: 0.2
RoundedButton:
text: 'Choose File'
size_hint_x: 0.2
TextInput:
id: get_file
readonly: True
size_hint_x: 0.5
Label:
text: ''
size_hint_x: 0.1
Label:
text: ''
size_hint_x: 0.2
RoundedButton:
text: 'Import'
size_hint_x: 0.2
Label:
text: ''
size_hint_x: 0.6
StackLayout:
id: import_data_content
orientation: 'lr-tb'
size_hint_y: None
height: 90
Screen:
id: calculate_scrn
name: 'calculate_scrn'
Screen:
id: settings_scrn
name: 'settings_scrn'
StackLayout:
orientation: 'lr-tb'
size_hint_x: 0.5
Label:
text: ''
size_hint_x: 0.1
Button:
text: 'Add Employee'
size_hint_x: 0.2
Label:
text: ''
size_hint_x: 0.2
Button:
text: 'CSV'
size_hint_x: 0.2
Label:
text: ''
size_hint_x: 0.3
BoxLayout:
orientation: 'horizontal'
size_hint_x: 0.5
Label:
text: 'In Time'
size_hint_x: 0.7
TextInput:
size_hint_x: 0.3
Label:
text: 'Out Time'
size_hint_x: 0.7
TextInput:
size_hint_x: 0.3
""")
class TabbedContainer(ToggleButton):
pass
class FileChoosePopup(Popup):
load = ObjectProperty()
class RoundedButton(Button):
pass
class RoundedCancelButton(Button):
pass
class RoundedAcceptButton(Button):
pass
class Tab(StackLayout):
file_path = StringProperty("No file chosen")
the_popup = ObjectProperty(None)
def __init__(self, **kwargs):
super().__init__(**kwargs)
#load import window on initialisation
import_window = self.ids.import_scrn
self.ids.scrn_man.current = 'import_scrn'
def change_screen(self, instance):
if instance.text == 'Import':
self.ids.scrn_man.current = 'import_scrn'
elif instance.text == 'Calculate':
self.ids.scrn_man.current = 'calculate_scrn'
else:
self.ids.scrn_man.current = 'settings_scrn'
class TestApp(App):
def build(self):
return Tab()
if __name__ == '__main__':
TestApp().run()
I expect that the import screen must show on initialisation and screens transition on toggle button state: down. Can someone please give me some advice on how to make my App act as explained above?

Your screens are loading correctly according to your settings. You need to review your entire kv string looking at your size_hint settings. Check each item that contains children and make sure that the total of size_hint_x for its children is less than or equal to 1.0 and the same for size_hint_y.

How to change text of a label in the kivy language with python

I was wondering how I could change the text of a label made inside the Kivy language using Python.
Like how would I have user input from python be made as the text of a label in kivy.
(By the way I have the formatting correct in the actual program but I screwed up pasting it to stackoverflow)
Say if I wanted to make the text of the label in from the code be a random number generated in python how would I go about doing that?
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.graphics import Color, Rectangle
from kivy.properties import ObjectProperty
# Create both screens. Please note the root.manager.current: this is how
# you can control the ScreenManager from kv. Each screen has by default a
# property manager that gives you the instance of the ScreenManager used.
Builder.load_string("""
<ButImage#ButtonBehavior+AsyncImage>
<TutImage#ButtonBehavior+AsyncImage>
<MenuScreen>:
GridLayout:
cols: 4
row_force_default: True
col_default_width: 175
row_default_height: 150
padding: 15
spacing: 15
canvas.before:
BorderImage:
# BorderImage behaves like the CSS BorderImage
border: 10, 10, 10, 10
source: '/Users/clayhigh/Desktop/kivy/aot.png'
pos: self.pos
size: self.size
Button:
text: 'Goto settings'
background_color: 1,0,0,0.5
on_press: root.manager.current = 'settings'
ButImage:
on_press: root.manager.current = 'UBW'
id: but
size_hint: .5, .5
opacity: 1 if self.state == 'normal' else .5
allow_stretch: True
keep_ratio: False
source: 'http://s3.amazonaws.com/rapgenius/1361742626_beautiful-ocean-beautiful-pictures-27115524-1440-900.jpg'
Label:
center: but.center
text: "UBW"
color: 0.78,0.145,0.016,2
ButImage:
id: lh
size_hint: .5, .5
opacity: 1 if self.state == 'normal' else .5
allow_stretch: True
keep_ratio: False
source: 'http://s3.amazonaws.com/rapgenius/1361742626_beautiful-ocean-beautiful-pictures-27115524-1440-900.jpg'
Label:
center: lh.center
text: "LH 2"
color: 0,0,0,1
ButImage:
id: ttl
size_hint: .5, .5
opacity: 1 if self.state == 'normal' else .5
allow_stretch: True
keep_ratio: False
source: 'http://s3.amazonaws.com/rapgenius/1361742626_beautiful-ocean-beautiful-pictures-27115524-1440-900.jpg'
Label:
center: ttl.center
text: "TwTl"
color: 0,0,0,1
ButImage:
id: gris
size_hint: .5, .5
opacity: 1 if self.state == 'normal' else .5
allow_stretch: True
keep_ratio: False
source: 'http://s3.amazonaws.com/rapgenius/1361742626_beautiful-ocean-beautiful-pictures-27115524-1440-900.jpg'
Label:
center: gris.center
text: "Gris"
color: 0,0,0,1
ButImage:
id: shig
size_hint: .5, .5
opacity: 1 if self.state == 'normal' else .5
allow_stretch: True
keep_ratio: False
source: 'http://s3.amazonaws.com/rapgenius/1361742626_beautiful-ocean-beautiful-pictures-27115524-1440-900.jpg'
Label:
center: shig.center
text: "Shig"
color: 0,0,0,1
Button:
text: 'Test3'
background_color: 1,0,0,0.5
Button:
text: 'Test4'
background_color: 1,0,0,0.5
Button:
text: 'Quit'
background_color: 1,0,0,0.5
on_press: App.on_stop
<SettingsScreen>:
GridLayout:
row_force_default: True
row_default_height: 100
cols: 2
canvas.before:
BorderImage:
# BorderImage behaves like the CSS BorderImage
border: 10, 10, 10, 10
source: '/Users/clayhigh/Desktop/kivy/ato.jpeg'
pos: self.pos
size: self.size
Button:
text: 'Button'
color: 0,0,.5
background_color: 1,0,0,1
Button:
text: 'Back to menu'
background_color: 1,0,0,1
on_press: root.manager.current = 'menu'
<UBW>:
GridLayout:
row_force_default: True
row_default_height: 100
cols: 2
canvas.before:
Color:
rgb: .5, .5, .5
Rectangle:
pos: self.pos
size: self.size
Color:
rgb: 1, 1, 1
BorderImage:
# BorderImage behaves like the CSS BorderImage
border: 10, 10, 10, 10
source: '/Users/clayhigh/Desktop/kivy/fsn.jpg'
pos: self.pos
size: self.size
Button:
text: 'Back to menu'
color: 0,0,.5
on_press: root.manager.current = 'menu'
background_color: 1,0,0,1
Label:
id: AName
text: "F S/N: UBW"
font_size: '24sp'
""")
# Declare both screens
class MenuScreen(Screen):
pass
class SettingsScreen(Screen):
pass
class UBW(Screen):
pass
# Create the screen manager
sm = ScreenManager()
sm.add_widget(MenuScreen(name='menu'))
sm.add_widget(SettingsScreen(name='settings'))
sm.add_widget(UBW(name='UBW'))
class TestApp(App):
def build(self):
return sm
if __name__ == '__main__':
TestApp().run()

Text of a label can be a kivy property, which can be later changed and since it is a kivy property it will automatically updated everywhere. Here is an example of your .py
from kivy.app import App
from kivy.uix.widget import Widget
from kivy.properties import StringProperty
import random
class YourWidget(Widget):
random_number = StringProperty()
def __init__(self, **kwargs):
super(YourWidget, self).__init__(**kwargs)
self.random_number = str(random.randint(1, 100))
def change_text(self):
self.random_number = str(random.randint(1, 100))
class YourApp(App):
def build(self):
return YourWidget()
if __name__ == '__main__':
YourApp().run()
and your .kv
<YourWidget>:
BoxLayout:
size: root.size
Button:
id: button1
text: "Change text"
on_release: root.change_text()
Label:
id: label1
text: root.random_number
When you click the button, it will call change_text() function, which will randomly change the text of the label to random integer between 1 and 100.