python - 了解 kivy 中的绑定(bind)

Question

我想了解有关绑定(bind)方法的更多信息

我不明白为什么该代码不起作用，(我将我的问题简化为这个，以帮助我理解原因)，非常感谢您的时间

from kivy.app import App
from kivy.uix.gridlayout import GridLayout


class Game(GridLayout):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.a = 0

        self.bind(a=self.f)

    def f(self, *args):
        print("ok")


class TestApp(App):
    def build(self):
        self.game = Game()
        return self.game


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

Traceback (most recent call last):
    File "test2.py", line 23, in <module>
        TestApp().run()
    File "C:\Users\Legion\AppData\Local\Programs\Python\Python37-32\lib\site-packages\kivy\app.py", line 829, in run
        root = self.build()
    File "test2.py", line 18, in build
        self.game = Game()
    File "test2.py", line 10, in __init__
        self.bind(a=self.f)
    File "kivy\_event.pyx", line 427, in kivy._event.EventDispatcher.bind
KeyError: 'a'

Answer 1

如果docs已审核:

bind(**kwargs)
Bind an event type or a property to a callback

_{(已添加强调)}

如上所述，它由与类的属性不同的属性表示。

因此，使用您的代码作为基础并添加每秒更改值的功能:

from kivy.app import App
from kivy.uix.gridlayout import GridLayout
from kivy.properties import NumericProperty
from kivy.clock import Clock

class Game(GridLayout):
    a = NumericProperty(0)

    def __init__(self, **kwargs):
        super().__init__(**kwargs)

        self.bind(a=self.f)

    def f(self, *args):
        print("ok")


class TestApp(App):
    def build(self):
        Clock.schedule_interval(self.foo, 1)
        self.game = Game()
        return self.game

    def foo(self, dt):
        self.game.a += 1


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

<小时/>

为什么是 Properties使用过吗？

因为该类型的属性存储关联的回调(例如示例中的可调用 f)，然后当其值更改时调用与其绑定(bind)的所有回调。