how do i disable a widget based on the value of another widget in Kivy

Question

I have a Spinner widget in a .kv file and I need the value of this Spinner to enable another Spinner widget.

This is the code i have tried and it does not work and gives me a Syntax error:

CustLabel:
    text: "Aux LO Pump Status"


CustSpinner:
    id: auxlo
    text: "Select"
    values: ('On', 'Off')
    focus: True
    on_state: (self.auxlonum.disabled) if (self.auxlo == 'off')

CustLabel:
    text: "Aux LO Pump Number"

CustSpinner:
    id: auxlonum
    text: "Select"
    values: ('# 1', '# 2')
    focus: True

i would actually prefer the auxlonum widget to start off disabled and 'greyed out' and then only be enabled if the auxlo widget had 'on' selected, however i was not sure how to go about this.

Thank you.

Answer 1

First, you can´t use on_state event because it emit before you selected one value. You need use on_text event instead.

On the other hand, self.auxlonum is an incorrect syntax, you should use the id only to refer to any widget inside kv.

Finally, you only need to use the ternary operator syntax to do what you want:

Spinner:
    id: auxlo
    on_text: auxlonum.disabled = True if auxlo.text == 'Off' else False

Or:

Spinner:
    id: auxlonum
    disabled: True if auxlo.text == 'Off' else False

Executable example:

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout

from kivy.lang import Builder


Builder.load_string('''
<MyWidget>
    orientation: 'vertical'
    Spinner:
        id: auxlo
        text: "Select"
        values: ('On', 'Off')
        focus: True
        on_text: auxlonum.disabled = True if auxlo.text == 'Off' else False

    Label:

    Spinner:
        id: auxlonum
        text: "Select"
        values: ('# 1', '# 2')
        focus: True

    Label:
''')


class MyWidget(BoxLayout):
    pass

class TestApp(App):
    def build(self):            
        return  MyWidget()

TestApp().run()