Kivy 外部规则继承 2

问题描述

作为后续问题:

• Kivy 外部规则继承
• 使用 add_widget() 继承 Kivy 规则李>

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

在上面的示例中，'on_release: self.imp.NoInspiration(':)')' 有效，因为 FancyButton 具有 'imp: root'.

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

但是 'font_name: self.imp.font_kanji' 不起作用并给出错误:

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

AttributeError: 'NoneType' 对象没有属性 'font_kanji'

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

我的猜测是这样做的原因是 on_release 发生在所有小部件都直接加载和 font_name 之后，所以没有'imp:root'.

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'.

我也试过了:

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

，但无济于事.

如何让 font_name 引用 font_kanji?我应该使用全局吗?如果是，您将如何在 Python 中设置可以在 .kv 中访问的全局?

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?

(如果我将 global 放在 font_Kanji 前面并删除 .kv 文件中的 'self.imp' 我会收到错误:NameError: name 'font_kanji' is not defined")

(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")

推荐答案

你的猜测是正确的:当你的按钮被创建时，它的 imp 属性是 None.解决这个问题的方法是观察 imp 属性并在其处理程序中设置 font_name 的值:

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

这样字体是在 imp 属性用适当的 Important 实例初始化之后设置的.这种方法的缺点是Instance.font_kanji的变化不会触发FancyButton.font_name的变化.

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.

如果你想绑定两个属性，那么你必须从 Instance.font_kanji 端调用 bind 函数(因为我们想对其更改做出反应)以动态创建 FancyButton 实例:

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)

kv语言定义的接口可以直接绑定:

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()
''')

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