Kivy: Don't know how to update "on_size: root.center = win.Window.center" in ScreenManager - kivy

Question

I added the Kivy scatter example to a kivy screen. But it didn´t work properly. I have to reconfigure the center on the window. It's done in the kv-file. But I don´t know how to do it on a screen. See the code below.
python
class Picture(Scatter):
source = StringProperty(None)
class ScreenThree(Screen):
def __init__(self, **kwargs):
super().__init__(**kwargs)
root = BoxLayout() # instantiate BoxLayout
self.add_widget(root) # add BoxLayout to screen
curdir = dirname(__file__)
for filename in glob(join(curdir, 'images', '*')):
print(filename)
try:
picture = Picture(source=filename, rotation=randint(-30, 25))
root.add_widget(picture)
except Exception as e:
Logger.exception('Pictures: Unable to load <%s>' % filename)
def on_pause(self):
return True
class TestApp(App):
def build(self):
sm = ScreenManager()
sc1 = ScreenOne(name='screen1')
sc2 = ScreenTwo(name='screen2')
sc3 = ScreenThree(name='screen3')
sm.add_widget(sc1)
sm.add_widget(sc2)
sm.add_widget(sc3)
print (sm.screen_names)
return sm
if __name__ == '__main__':
TestApp().run()
kivy
#:kivy 1.0
#:import kivy kivy
#:import win kivy.core.window
FloatLayout:
canvas:
Color:
rgb: 1, 1, 1
Rectangle:
source: 'data/images/background.jpg'
size: root.size
BoxLayout:
padding: 10
spacing: 10
size_hint: 1, None
pos_hint: {'top': 1}
height: 44
Image:
size_hint: None, None
size: 24, 24
source: 'data/logo/kivy-icon-24.png'
Label:
height: 24
text_size: self.width, None
color: (1, 1, 1, .8)
text: 'Kivy %s - Pictures' % kivy.__version__
<Picture>:
on_size: root.center = win.Window.center <-- this is the question i guess
size: image.size
size_hint: None, None
Image:
id: image
source: root.source
# create initial image to be 400 pixels width
size: 400, 400 / self.image_ratio
# add shadow background
canvas.before:
Color:
rgba: 1,1,1,1
BorderImage:
source: 'shadow32.png'
border: (36,36,36,36)
size:(self.width+72, self.height+72)
pos: (-36,-36)
See the example here, Kivy Gallery of Examples » Basic Picture Viewer

Answer 1

In the kv file, on_size: root.center = win.Window.center will work fine, when you make the instantiated object, FloatLayout: as child of class rule, <ScreenThree>: plus some enhancements in Python script.
kv file
Replace #:kivy 1.0 with the Kivy version installed e.g. #:kivy 1.11.1
Add class rule, <ScreenThree>: and make FloatLayout: object as child of <ScreenThree>:
Snippets - kv file
<ScreenThree>:
FloatLayout:
canvas:
Color:
rgb: 1, 1, 1
Rectangle:
source: 'data/images/background.jpg'
size: root.size
BoxLayout:
padding: 10
spacing: 10
size_hint: 1, None
pos_hint: {'top': 1}
height: 44
Image:
size_hint: None, None
size: 24, 24
source: 'data/logo/kivy-icon-24.png'
Label:
height: 24
text_size: self.width, None
color: (1, 1, 1, .8)
text: 'Kivy %s - Pictures' % kivy.__version__
py file
Remove root = BoxLayout() and self.add_widget(root)
Replace root.add_widget(picture) with self.add_widget(picture)
Snippets - py file
class ScreenThree(Screen):
def __init__(self, **kwargs):
super().__init__(**kwargs)
curdir = dirname(__file__)
for filename in glob(join(curdir, 'images', '*')):
print(filename)
try:
picture = Picture(source=filename, rotation=randint(-30, 25))
self.add_widget(picture)
except Exception as e:
Logger.exception('Pictures: Unable to load <%s>' % filename)
Output