这是一件有趣的事情：您不需要在 lang 本身中指定 kv lang 中使用的所有类 - 您也可以稍后在代码中使用 Factory.register 方法添加它们。这是一个例子：
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label
from kivy.lang import Builder
from kivy.factory import Factory
from functools import partial
Builder.load_string('''
<MyWidget>:
Foo
Bar
''')
class MyWidget(BoxLayout):
pass
class MyApp(App):
def build(self):
Factory.register('Foo', cls=partial(Label, text='foo'))
Factory.register('Bar', cls=partial(Label, text='bar'))
return MyWidget()
if __name__ == '__main__':
MyApp().run()
让我们用它来创建一个模板基础小部件，我们稍后会填充各种内容。我们使用一个占位符，稍后用另一个小部件替换：
<BaseWidget>:
orientation: 'vertical'
Label:
size_hint: None, 0.1
text: 'title'
Placeholder
在 Python 代码中，我们在此基本模板类的 __init__ 方法中注册了一个占位符类。
class BaseWidget(BoxLayout):
def __init__(self, **args):
# unregister if already registered...
Factory.unregister('Placeholder')
Factory.register('Placeholder', cls=self.placeholder)
super(BaseWidget, self).__init__(**args)
现在让我们定义一个内容类。
<TwoButtonWidget>:
Button:
text: 'button 1'
Button:
text: 'button 2'
最后创建一个自定义类，使用我们的基类作为模板，并将其占位符替换为内容类。这个类没有自己的 kivy 规则（这些规则被移到内容类中），所以当我们从基本模板继承时，不会插入额外的小部件。
# content class
class TwoButtonWidget(BoxLayout):
pass
# Base class subclass
class CustomizedWidget(BaseWidget):
placeholder = TwoButtonWidget # set contetnt class
一个完整的例子：
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.lang import Builder
from kivy.factory import Factory
Builder.load_string('''
<BaseWidget>:
orientation: 'vertical'
widget_title: widget_title
placeholder: placeholder
Label:
size_hint: None, 0.1
id: widget_title
Placeholder
id: placeholder
<TwoButtonWidget>:
button1: button1
Button:
text: 'button 1'
id: button1
Button:
text: 'button 2'
<ThreeButtonWidget>:
orientation: 'vertical'
Button:
text: 'button a'
Button:
text: 'button b'
Button:
text: 'button c'
''')
class BaseWidget(BoxLayout):
def __init__(self, **args):
# unregister if already registered...
Factory.unregister('Placeholder')
Factory.register('Placeholder', cls=self.placeholder)
super(BaseWidget, self).__init__(**args)
class TwoButtonWidget(BoxLayout):
pass
class ThreeButtonWidget(BoxLayout):
pass
class CustomizedWidget1(BaseWidget):
placeholder = TwoButtonWidget
class CustomizedWidget2(BaseWidget):
placeholder = ThreeButtonWidget
class MyApp(App):
def build(self):
layout = BoxLayout()
c1 = CustomizedWidget1()
# we can access base widget...
c1.widget_title.text = 'First'
# we can access placeholder
c1.placeholder.button1.text = 'This was 1 before'
c2 = CustomizedWidget2()
c2.widget_title.text = 'Second'
layout.add_widget(c1)
layout.add_widget(c2)
return layout
if __name__ == '__main__':
MyApp().run()
您可以轻松扩展它，例如，拥有多个占位符。
将此应用于您的案例：
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label
from kivy.lang import Builder
from kivy.factory import Factory
from functools import partial
Builder.load_string('''
<SimpleBar>:
canvas.before:
Color:
rgba: 0, 0.5, 0.5, 1
Rectangle:
pos: self.pos
size: self.size
BoxLayout:
Placeholder
Label:
text: "hi"
<NewBarContent>:
Label:
text: "2"
''')
class SimpleBar(BoxLayout):
def __init__(self, **args):
# unregister if already registered...
Factory.unregister('Placeholder')
Factory.register('Placeholder', cls=self.placeholder)
super(SimpleBar, self).__init__(**args)
class NewBarContent(BoxLayout):
pass
class NewBar(SimpleBar):
placeholder = NewBarContent
class MyApp(App):
def build(self):
return NewBar()
if __name__ == '__main__':
MyApp().run()