How can I add widgets to an existing screen? - python-3.x

Question

my application is built from a .kv file.
I want to add buttons to a Screen from my python file.
class Profiles(Screen):
def suh(self):
for i in range(5):
self.add_widget(Button(text=i))
The suh function seem to have no effect. Is this because the function is called after the app is built? Is there a better way to do this?

Answer 1

Solution 1
Since Screen is a RelativeLayout, use on_pre_enter or on_enter to inovke method, suh(), plus add size and pos to Button widget.
Solution 2
Use a container e.g. BoxLayout or Gridayout on top of Screen.
Note
Whenever widget is added to a screen via on_pre_enter or on_enter, use on_pre_leave or on_leave to remove the widget. This is to prevent doubling your widget each time the screen is entered.
If the widgets are cleared too fast, use Clock.schedule_once with a time interval.
Note 1: Screen Events
Kivy Screen has the following events.
Kivy Screen » Events
on_pre_enter: ()
Event fired when the screen is about to be used: the entering
animation is started.
on_enter: ()
Event fired when the screen is displayed: the entering animation is
complete.
on_pre_leave: ()
Event fired when the screen is about to be removed: the leaving
animation is started.
on_leave: ()
Event fired when the screen is removed: the leaving animation is
finished.
Note 2: Screen is a RelativeLayout
Kivy Screen » RelativeLayout
Please note that by default, a Screen displays nothing: it’s just
a RelativeLayout. You need to use that class as a root widget for
your own screen, the best way being to subclass.
Warning
As Screen is a RelativeLayout, it is important to understand
the Common Pitfalls.
Example - Solution 1
main.py
from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.button import Button
from kivy.lang import Builder
Builder.load_string("""
<Profiles>:
# on_pre_enter: self.suh()
on_enter: self.suh()
""")
class Profiles(Screen):
def suh(self):
for i in range(5):
self.add_widget(Button(text=str(i), size_hint=(0.1, 0.1), pos=(i*100, i*100)))
sm = ScreenManager()
sm.add_widget(Profiles(name='profiles'))
class TestApp(App):
def build(self):
return sm
if __name__ == "__main__":
TestApp().run()
Output - Solution 1
Example - Solution 2
main.py
from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.button import Button
from kivy.lang import Builder
Builder.load_string("""
<Profiles>:
# on_pre_enter: self.suh()
on_enter: self.suh()
BoxLayout:
id: container
""")
class Profiles(Screen):
def suh(self):
for i in range(5):
self.ids.container.add_widget(Button(text=str(i), size_hint=(0.1, 0.1)))
sm = ScreenManager()
sm.add_widget(Profiles(name='profiles'))
class TestApp(App):
def build(self):
return sm
if __name__ == "__main__":
TestApp().run()
Output - Solution 2

Answer 2

Add the widgets through the App class in stead of the Screen. So you would have to create a function that creates the widgets, and in your build function, you would have to use Clock.schedule_once from the Clock module to run the other function. Example:
class TestApp(App):
def build(self):
Clock.schedule_once(self.yoyo, 0)
return MainWin()
def yoyo(self, *args):
for i in memu_acc:
self.root.ids["prof"].ids["pro"].add_widget(Button(text=i))