How can I implement a scrolling label in Kivy without using Builder (or a .kv file)? - kivy

Question

I am trying to implement a scrolling label in a Kivy program, and found this example (slightly modified) that works:
from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.scrollview import ScrollView
from kivy.properties import StringProperty
from kivy.lang import Builder
long_text = "".join(["this is a long line "+str(n)+"\n" for n in range(1,101)])
Builder.load_string('''
<ScrollableLabel>:
Label:
size_hint_y: None
height: self.texture_size[1]
text_size: self.width, None
text: root.text
''')
class ScrollableLabel(ScrollView):
text = StringProperty('')
class ScrollApp(App):
def build(self):
return ScrollableLabel(text=long_text)
if __name__ == "__main__":
ScrollApp().run()
Partly for my own education, I am trying to convert this sample to not use Builder (and not resort to a .kv file). I have modified the above example to:
from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.scrollview import ScrollView
from kivy.properties import StringProperty
long_text = "".join(["this is a long line "+str(n)+"\n" for n in range(1,101)])
class ScrollableLabel(ScrollView):
text = StringProperty('')
def __init__(self, **kwargs):
super(ScrollableLabel, self).__init__(**kwargs)
self.label = Label(size_hint_y=None, text=self.text)
self.label.height = self.label.texture_size[1]
self.label.text_size = (self.label.width, None)
self.add_widget(self.label)
class ScrollApp(App):
def build(self):
return ScrollableLabel(text=long_text)
if __name__ == "__main__":
ScrollApp().run()
To my obviously untutored eye, these programs look like they should be equivalent. However, my (second) version doesn't work correctly (on several fronts).
So my question is two-fold: why doesn't the second version work the same as the first, and (if the answer isn't obvious from the first), how can I make it do so?
Thanks! -David

Answer 1

Try this:
from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.scrollview import ScrollView
from kivy.properties import StringProperty
from kivy.clock import Clock
long_text = "".join(["this is a long line "+str(n)+"\n" for n in range(1,101)])
class ScrollableLabel(ScrollView):
text = StringProperty('')
def __init__(self, **kwargs):
super(ScrollableLabel, self).__init__(**kwargs)
self.label = Label(size_hint_y=None, text=self.text)
self.add_widget(self.label)
Clock.schedule_once(self.update, 1)
def update(self, *args):
self.label.text_size = (self.label.width, None)
self.label.height = self.label.texture_size[1]
class ScrollApp(App):
def build(self):
return ScrollableLabel(text=long_text)
if __name__ == "__main__":
ScrollApp().run()
the output now is the same as your first