kivy NumericProperty问题

Question

I am working on incrementer app, and this is my code.

from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.gridlayout import GridLayout
from kivy.uix.label import Label
from kivy.properties import NumericProperty

value = NumericProperty(0)

class documentScreen(GridLayout):
    def __init__(self, **kwargs):
        super(documentScreen, self).__init__(**kwargs)

        self.cols = 1
        self.inc = Button(text='++')
        self.add_widget(self.inc)
        self.add_widget(Label(text=str(value)))

class MainScreen(App):
    def build(self):
        return documentScreen()

if __name__=='__main__':
    MainScreen().run()

but when i an run the code, Label display as <NumericProperty name=> instead of 0. It's doesn't display 0.

Answer 1

Kivy properties are defined at class level. So you need to put your NumericProperty one line above the init method of your DocumentScreen class. You made it a global variable which doesn't make sense.