CODEWITHSUNDEEP
pythonpropertiesbindkivy
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Reputation: 323

Understanding Kivy properities and binding methods

I am having problems understanding the usage of custom Properities and ways of binding methods to events. Here's my code:

from kivy.app import App
from kivy.lang import Builder

from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label
from kivy.uix.button import Button
from kivy.properties import StringProperty

kivy_lang = '''
<MainWidget>:
    on_my_property: my_label.text = 'from button bind method via StringProperty' + my_property

    Label:
        id: my_label
        text: root.my_property
    Button:
        id: my_button
        text: 'intro button'

'''


class MainWidget(BoxLayout):
    # bind some properties
    my_property = StringProperty('0')

    def __init__(self, **kwargs):
        super(MainWidget, self).__init__(**kwargs)
    #     if needed to do sth on widget construction
        self.ids.my_button.bind(on_press=self.my_method)


    def my_method(self,*args,**kwargs):
        self.my_property = str(int(self.my_property)+1)
        self.ids.my_button.text = 'new'


class MyApp(App):
    def build(self):
        Builder.load_string(kivy_lang)
        return MainWidget()

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

When I run it it renders OK, but when I click a button, as a result I get NameError: name 'my_property' is not defined

I tried binding method for Button in kv lang with (and removing whole 'init()' on python side):

on_press: root.my_method

and then when I press button the app doesn't crash but nothing happens

Can someone explain me how to adjust this code to work? I understand the code is a little 'mixed techniques' but I did it that way to get to know different approaches, so I would appreciate if You don't turn it all around :)

Upvotes: 0

Views: 1186

Answers (1)

Tshirtman
Tshirtman

Reputation: 5947

1/ you are missing 'self' before 'my_property' in 'on_my_property' bindind, hence the crash

2/ in kv bindings. the python code is called as written, so you need '()' after 'root.my_method', or the statement has no effect.

Upvotes: 1

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