Tyro
I am at sea again in trying to refer to widgets both within and outside of the class in which they’re created. I was able to do so before I incorporated screens into my program, having been taught to use the App.get_running_app() method, but that doesn’t seem to work now. In this scaled-down code example, I use two screens, one created within the Python code and one in a kv file. I’ve highlighted three examples of the problem I’m having.
Hoping for guidance. Thanks.
kv file:
<CustButton@Button>:
font_size: 40
color: 0, 0, 0, 1
background_normal: ''
background_color: .3, .3, 1,1
<FirstScreen>:
BoxLayout:
orientation: 'vertical'
BoxLayout:
padding: 200
CustButton:
id: switch_button
text: "screen switch
button"
on_press:
root.manager.current = 'second'
Python:
from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.dropdown import DropDown
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.uix.textinput import TextInput
user_list = ['alpha','beta','gamma']
class SecondScreen(Screen):
def __init__(self, **kwargs):
super(SecondScreen, self).__init__(**kwargs)
b = BoxLayout(orientation='vertical', padding=500)
t = TextInput(id='my_text', height='60dp', cursor_width="2sp")
dropdown = DropDown()
for index in range(len(user_list)):
btn = Button(text=user_list[index], size_hint_y=None, height=44)
btn.bind(on_release=lambda btn: dropdown.select(btn.text))
dropdown.add_widget(btn)
mainbutton = Button(text='Names')
mainbutton.bind(on_release=dropdown.open)
dropdown.bind(on_select=lambda instance, x: setattr(t, 'text', x))
b.add_widget(t)
b.add_widget(mainbutton)
l=Label(height='60dp') #spacer
b.add_widget(l)
j= Button(text ="switch back")
#j.bind(on_release=outside_function())
j.bind(on_release=self.switcher)
b.add_widget(j)
self.add_widget(b)
def switcher(self,obj):
global user
self.manager.current = 'first'
# 1) If I try this:
user = self.t.text
# I get: AttributeError: 'SecondScreen' object has no attribute 't'
# 2) If I try this:
app_ref = App.get_running_app()
user = app_ref.root.ids.t.text
# I get: AttributeError: 'super' object has no attribute '__getattr__'
# 3) If I call this function from within SecondScreen class and try to refer to a widget:
def outside_function():
app_ref = App.get_running_app()
app_ref.root.ids.switch_button.disabled = True
# I get: AttributeError: 'NoneType' object has no attribute 'ids'
class FirstScreen(Screen):
pass
class TestApp(App):
def build(self):
sm = ScreenManager()
sm.add_widget(FirstScreen(name='first'))
sm.add_widget(SecondScreen(name='second'))
return sm
if __name__ == '__main__':
TestApp().run()
Monty Mole
example below, all 3 references in def callback_rvbtn(self) work.
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.recycleview import RecycleView
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
Builder.load_string('''
<MainInterface>:
orientation: 'vertical'
Label:
text: 'Recycleviewtest'
font_size: '20'
size_hint: 1,.1
text_size: self.size
Label:
id: stat
text: 'status here...'
font_size: '20'
size_hint: 1,.1
text_size: self.size
RecycleView:
id: rv
viewclass: 'myButton'
RecycleBoxLayout:
orientation: 'vertical'
default_size: None, dp(40)
default_size_hint: 1, None
size_hint_y: None
height: self.minimum_height
Button:
text: 'Press me'
size_hint_y: 0.1
on_release: root.callback_btn(self)
<myButton>:
on_release:self.callback_rvbtn()
''')
root = None
stat = None
class myButton(Button):
def callback_rvbtn(self):
#self.parent.parent.parent.ids.stat.text = 'btn recycle pressed: %s' %self.text
#root.ids.stat.text = 'btn recycle pressed: %s' %self.text
stat.text = 'btn recycle pressed: %s' %self.text
class MainInterface(BoxLayout):
def __init__(self, **kwargs):
super(MainInterface, self).__init__(**kwargs)
self.ids.rv.data = [{'text': str(x)} for x in range(200)]
def callback_btn(self,btn):
self.ids.rv.data = [{'text': 'yo !'} for x in range(200)]
class TestApp(App):
def build(self):
global root
global stat
root = MainInterface()
stat = root.ids.stat
return root
Tyro
Monty Mole
without looking too much into your code I wonder why you dont declare everything in the kv file ? You could start with the screenmanager and then put the screens under it with ids to reference each...
something like this:
<MaintInterface>:
ScreenManager:
id: screenmanager
Screen:
name: 'screen1'
id: screen1
BoxLayout:
......
Screen:
name: 'screen2'
id: screen2
BoxLayout:
......
in order to access the instances of those classes you can keep the reference to the main instance and then access all other instances by their ids:
class Loader(App):
def build(self):
global root
Builder.load_file(kvfile)
root = MainInterface()
return root
and then later:
root.ids['screenmanager'].current='screen1'
learn kv... it' easier ... do your gui stuff in kv and the logic in the python part...
and btw: the good thing about classes is that they are encapsulated ... the bad thing is that they are encapsulated :)
Tyro
user_list = []
try:
with open('user.dat', 'rb') as f:
user_data = pickle.load(f)
for i in user_data:
user_list.append(i[0])
except:
user_list = []
class SecondScreen(Screen):
def __init__(self, **kwargs):
super(SecondScreen, self).__init__(**kwargs)
b = BoxLayout(orientation = 'vertical', padding = '100dp')
t = TextInput(id = 'my_text', size_hint_y = None, halign = 'middle', valign = 'middle', height = '60dp')... (more stuff here)
ZenCODE
for index in range(len(user_list)):
self.btns = [Button(text=user_list[index], size_hint_y=None, height=44) for index in range(len(user_list)]
[drop_down.add_widget(btn) for btn in self.btns]
Now you should be able to access those buttons via self.manager.current_screen.btns[0] etc. There are other ways of course, but that should work?
Tyro
Matthew Einhorn
Thanks for your help. What I want is to be able to refer to *any* widget from *any* part of my program, for example, get the text in t, the text widget, regardless of which method is referring to it, whether the method is in the current screen's class or that of another screen, or outside of both. I'd like to be able to do this from any method or function anywhere in the program. This seems fundamental.Before I introduced screens, I was able to do all this with the App.get_running_app() method. (So, to get the text in t: user = app_ref.root.ids.t.text). I don't know why this doesn't work now that my classes are within screens (if that's the right way to phrase it). But I'd happily accept anything equivalent!
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Tyro
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Monty Mole
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.recycleview import RecycleView
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
Builder.load_string('''
<MainInterface>:
Screen:
BoxLayout:
orientation: 'vertical'
Label:
id: statlabel
text: ''
Button:
text: 'btn1'
on_release: root.callback_btn_insideroot(self)
ButtonOutsideRoot:
text: 'btn2'
on_release: self.callback_btn_outsideroot()
ButtonOutsideRoot:
text: 'btn3'
on_release: self.callback_btn_outsideroot()
ButtonOutsideRoot:
text: 'btn4'
on_release: self.callback_btn_outsideroot()
''')
class ButtonOutsideRoot(Button):
def callback_btn_outsideroot(self): # no args given so the reference to the root interface(ScreenManager) has has to be found otherwise
if self.text == 'btn2': # self refers to the calling class automatically
main.ids.statlabel.text = 'referenced by global main %s' %self.text
elif self.text == 'btn3':
App.get_running_app().root.ids.statlabel.text = 'referenced by App.get_running_app() %s' %self.text
if self.text == 'btn4':
self.parent.parent.parent.ids.statlabel.text = 'refereced by kivy tree %s' %self.text
class MainInterface(ScreenManager):
def callback_btn_insideroot(self,btn):
if btn.text == 'btn1':
self.ids.statlabel.text = 'self referecenced by callback %s' %btn.text
class ExampleApp(App):
def build(self):
global main
main = MainInterface() # global main reference
return main
if __name__ == '__main__':
ExampleApp().run()
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Tyro
main = None
class ButtonOutsideRoot(Button):
global main
def callback_btn_outsideroot(self): # no args given so the reference to the root interface(ScreenManager) has has to be found otherwise
if self.text == 'btn2': # self refers to the calling class automatically
main.ids.statlabel.text = 'referenced by global main %s' %self.text
elif self.text == 'btn3':
App.get_running_app().root.ids.statlabel.text = 'referenced by App.get_running_app() %s' %self.text
if self.text == 'btn4':
self.parent.parent.parent.ids.statlabel.text = 'refereced by kivy tree %s' %self.text
class MainInterface(ScreenManager):
def callback_btn_insideroot(self,btn):
if btn.text == 'btn1':
self.ids.statlabel.text = 'self referecenced by callback %s' %btn.text
print untersuche(self)
Monty Mole
Tyro
ZenCODE
from kivy.uix.screenmanager import ScreenManager
Builder.load_string('''
<MainInterface>:
Screen:
BoxLayout:
orientation: 'vertical'
Label:
id: statlabel
text: ''
Button:
text: 'btn1'
on_release: root.callback_btn_insideroot(self)
ButtonOutsideRoot:
text: 'btn2'
ButtonOutsideRoot:
text: 'btn3'
on_release: root.callback_btn_insideroot(self)
ButtonOutsideRoot:
text: 'btn4'
on_release: root.callback_btn_insideroot(self)
''')
class ButtonOutsideRoot(Button):
pass
class MainInterface(ScreenManager):
def callback_btn_insideroot(self, btn):
self.ids.statlabel.text = 'Screen = {0}, button = {1}'.format(self, btn)
class ExampleApp(App):
def build(self):
Monty Mole
Tyro
I’ve made good progress, thanks to numerous helpful explanations--I (believe I) can now access any widget from any class.
I have a new problem, though. The code below is a minimal version of my program. I can get either of its two screens to display by setting current screen in the app build. And if I start with SecondScreen, I can switch to FirstScreen. However, I can’t go the other direction—If I start with FirstScreen and its button is clicked, only a black screen appears. What do I have wrong here? (FirstScreen has to be constructed within the Python code rather than in the kv file, because in the actual program I load the button texts from a file.)
Another, less serious problem: If I start with FirstScreen, the other one (SecondScreen) appears for a fraction of a second before FIrstScreen is displayed. Maybe related to the first problem? Thanks for any edification.
import kivy
kivy.require('1.9.0')from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.dropdown import DropDown
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.uix.textinput import TextInput
from kivy.lang import Builder
Builder.load_string('''
<CustButton@Button>:
font_size: 40
color: 0, 0, 0, 1
background_normal: ''
background_color: .3, .3, 1,1
height: "130dp"
size_hint_y: None
<MainInterface>:
padding: 50
switch_button: switch_button
exit_button: exit_button
SecondScreen:
BoxLayout:
spacing: 20
CustButton:
id: switch_button
text: "Switch to FirstScreen"
on_release: root.current = "first"
CustButton:
id: exit_button
background_color: [.71, .086, .075,1]
text: "Exit"
on_release: app.stop()
''')
class MainInterface(ScreenManager):
pass
class SecondScreen(Screen):
pass
class FirstScreen(Screen):
def __init__(self, **kwargs):
super(FirstScreen, self).__init__(**kwargs)
players_list = ['alpha', 'beta', 'gamma']
b = BoxLayout(orientation='vertical', padding=500)
self.txt = TextInput(id='my_text', height='60dp', cursor_width="2sp")
dropdown = DropDown()
for index in range(len(players_list)):
btn = Button(text=players_list[index], size_hint_y=None, height=44)
btn.bind(on_release=lambda btn: dropdown.select(btn.text))
dropdown.add_widget(btn)
mainbutton = Button(text='Names')
mainbutton.bind(on_release=dropdown.open)
dropdown.bind(on_select=lambda instance, x: setattr(self.txt, 'text', x))
b.add_widget(self.txt)
b.add_widget(mainbutton)
l=Label(text = '')
b.add_widget(l)
j= Button(text ="switch to SecondScreen")
j.bind(on_release=self.fetch_name)
b.add_widget(j)
self.add_widget(b)
def fetch_name(self,obj):
app_ref = App.get_running_app()
app_ref.root.ids.switch_button.text = self.txt.text
main.current = 'second'
class MinimalApp(App):
def build(self):
global main
main = MainInterface()
main.add_widget(FirstScreen(name='first'))
main.add_widget(SecondScreen(name='second'))
main.current = 'first'
return main
if __name__ == '__main__':
MinimalApp().run()
Monty Mole
because I couldnt figure out what exactly was wrong with your code and to see how it would look like, I reworked the code and it mostly works. This is what I did:
- tried to put most stuff in kv
- tried to move all calls to the main layout class so everything is in one place in main (global)
- put the dynamic dropdown in __init__ of the main layout. (so everything is in one place...)
- put ??? behind lines with possible errors
When I started with kivy I did it exactly like you (doing most gui stuff in code) until I realised that it just gets very complicated when your code grows and even worse when you have to rework the complete layout.
I have an app that has a different layouts with different screens when started on tablet or phone and found it unpossible to do everything dynamicall in python code. Now I just load two different kv files.
And as you can see, you can always add additional widget with add_widget later.
hope this helps
# ---------------------------------------------------------------------------------------------------------------------------------------
import kivy
kivy.require('1.9.0')
from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.dropdown import DropDown
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.uix.textinput import TextInput
from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout
Builder.load_string('''
<MainInterface>:
padding: 50
#switch_button: switch_button # ???
#exit_button: exit_button
Screen:
id: firstscreen
name:'first'
BoxLayout:
orientation:'vertical'
padding: 50 # ??? instead of 500 thats why you got a black screenn
TextInput:
id: txt
height:'60dp'
cursor_width:"2sp"
Button:
text: 'Names'
on_release: root.dropdown.open(root.ids.txt)
Label:
text: 'Label here'
Button:
text: "switch to SecondScreen"
on_release: root.fetch_name()
Screen:
name: 'second'
id: secondscreen
BoxLayout:
spacing: 20
CustButton:
id: switch_button
text: 'Switch to FirstScreen'
size_hint_y: .1
CustButton:
id: exit_button
background_color: .71, .086, .075,1
text: "Exit"
on_release: app.stop()
<CustButton@Button>:
font_size: 40
color: 0, 0, 0, 1
background_normal: ''
background_color: .3, .3, 1,1
height: "130dp"
size_hint_y: None
class MainInterface(ScreenManager):
def __init__(self, **kwargs):
super(MainInterface, self).__init__(**kwargs)
players_list = ['alpha', 'beta', 'gamma']
for index in range(len(players_list)):
btn = Button(text=players_list[index], size_hint_y=None, height=44)
self.dropdown.add_widget(btn)
self.dropdown.bind(on_select=lambda instance, x: setattr(main.ids.txt, 'text', x)) # somethin was wrong here and broke the screenmanager
def fetch_name(self):
pass
#app_ref = App.get_running_app() #you dont need this becaus you already have it in the global main var
#app_ref.root.ids.switch_button.text = self.txt.text
main.ids.switch_button.text = main.ids.txt.text
main.current = 'second'
class MinimalApp(App):
def build(self):
global main
main = MainInterface()