Animating objects via ID in kivy - kivy

Question

I am trying to animate a graphic in kivy. Since all my inputs will be coming from the keyboard, I need to have object references in python, however I still want to set up the widgets in the kv file. To do this I found the only way to trigger anything from python was using IDs. However when trying to start an animation via ID the object doesn't move. Printing the x coordinate shows a change, although I don't see it move.
Here is my main.py:
import threading
import time
import keyboard
from kivy.app import App, ObjectProperty
from kivy.uix.screenmanager import Screen, ScreenManager, NoTransition
from kivy.uix.floatlayout import FloatLayout
from kivy.animation import Animation, AnimationTransition
class MainScreen(Screen):
pass
class OtherScreen(Screen):
pass
def left_animate(object):
anim = Animation(x=object.x - 40, transition='in_back')
anim.start(object)
class RootWidget(FloatLayout):
def __init__(self, **kwargs):
super(RootWidget, self).__init__(**kwargs)
self.screenman = ScreenManager()
self.screenman.add_widget(MainScreen(name="main"))
self.screenman.add_widget(OtherScreen(name="other"))
self.add_widget(self.screenman)
x = threading.Thread(target=self.keyboard_thread)
x.start()
def keyboard_thread(self):
print("Thread started")
while True:
if keyboard.is_pressed('h'):
self.key_event('h')
elif keyboard.is_pressed('j'):
self.key_event('j')
elif keyboard.is_pressed('left'):
self.left_pressed()
def left_pressed(self):
if self.screenman.current == 'main':
anim = Animation(x = 40)
print(self.ids.main.ids.img_ok.x)
anim.start(self.ids.main.ids.img_ok)
def key_event(self, key):
if key == 'h':
self.screenman.current = "main"
else:
self.screenman.current = "other"
class TestApp(App):
def build(self):
return RootWidget()
if __name__ == '__main__':
TestApp().run()
and this is the .kv file:
<RootWidget>:
ScreenManager:
MainScreen:
id: main
OtherScreen:
id: other
<MainScreen>:
canvas.before:
Color:
rgba: 0, 0, 0, 1
canvas:
Rectangle:
pos: root.pos
size: root.size
Image:
id: img_ok
source: '../graphics/icons8-abstimmung-80.png'
pos: 200, 200
<OtherScreen>:
Button:
text: 'Go to main screen'
on_press: root.manager.current = 'main'

Answer 1

The first problem is that you are building two ScreenManagers. One is built in the __init__() method of RootWidget. The other is being built by kv when it evaluates the <RootWidget>: rule in your .kv file. Both of those ScreenManagers fill the RootWidget and one obscures the other. I believe that your Animation is moving the Image widget, but it is underneath and not visible.
I suggest that you start fixing this by eliminating:
self.screenman = ScreenManager()
self.screenman.add_widget(MainScreen(name="main"))
self.screenman.add_widget(OtherScreen(name="other"))
self.add_widget(self.screenman)
from the __init__() method. That will force additional changes to your code.