猕猴桃外部规则继承2

Question

As follow-up question to:

• Kivy outside rule inherence
• Kivy rule inherence with add_widget()

main.py

import os
from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.stacklayout import StackLayout
from kivy.properties import ObjectProperty


class FancyButton(Button):
    imp = ObjectProperty(None)


class Important(StackLayout):

    font_kanji = os.path.join('fonts', 'TakaoPMincho.ttf')

    def NoInspiration(self, smile):
        print("Received: {}".format(smile))

    def AddFancy(self):
        print(self.ids)
        temp = FancyButton(text='f', imp = self)
        self.ids.boxy.add_widget(temp)


class TestApp(App):
    def build(self):
        pass

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

test.kv

#:kivy 1.9.0

<FancyButton>:
    font_name: self.imp.font_kanji  # ERROR
    on_release: self.imp.NoInspiration(':)')  # WORKS


<Important>:
    id: imp

    BoxLayout:
        id: boxy
        orientation: 'vertical'

        FancyButton:
            text: "smiley"
            imp: root

        Button:
            text: "add fancy"
            on_release: imp.AddFancy()


BoxLayout:
    Important

In the above example 'on_release: self.imp.NoInspiration(':)')' works because FancyButton has 'imp: root'.

However 'font_name: self.imp.font_kanji' doesn't work and gives the error:

AttributeError: 'NoneType' object has no attribute 'font_kanji'

My guess is the reason for this is that on_release takes place after all widgets are loaded and font_name directly, so without having 'imp: root'.

I also tried:

font_kanji = StringProperty(os.path.join('fonts', 'TakaoPMincho.ttf'))

, but to no avail.

Question

How do I get font_name refer to font_kanji? Should I use global? If yes, how would you set a global in Python which can be accessed in the .kv?

(If I put global in front of font_Kanji and remove 'self.imp' in the .kv file I get the error: " NameError: name 'font_kanji' is not defined")

Answer 1

Your guess is right: when your button is created its imp property is None . One to go around this would be to observe imp property and set the value of font_name in its handler:

class FancyButton(Button):
    imp = ObjectProperty(None)

    def on_imp(self, obj, imp):
        if imp:
            self.font_name = imp.font_kanji

This way the font is set after imp property is initialzied with proper Important instance. The dissadvantage of this method is that changes of Instance.font_kanji won't trigger changes of FancyButton.font_name .

If you want to have both properties binded, then you have to call bind funtion from Instance.font_kanji side (since we want to react to its changes) for dynamically created FancyButton instances:

class Important(StackLayout):
    font_kanji = os.path.join('fonts', 'TakaoPMincho.ttf')

    def NoInspiration(self, smile):
        print("Received: {}".format(smile))

    def AddFancy(self):
        temp = FancyButton(text='f', imp = self)
        self.bind(font_kanji=temp.setter('font_name'))
        self.ids.boxy.add_widget(temp)

Interface defined in the kv language can do the binding directly:

<Important>:
    id: imp

    BoxLayout:
        id: boxy
        orientation: 'vertical'

        FancyButton:
            text: "smiley"
            font_name: root.font_kanji
            imp: root

        Button:
            text: "add fancy"
            on_release: imp.AddFancy()
''')