用于绘制数据的Kivy自定义小部件，无法获取当前小部件尺寸

from kivy.uix.widget import Widget

class MyWidget(Widget):
    def on_size(self, *args):
        print("当前小部件尺寸：", self.size)

from kivy.uix.widget import Widget

class MyWidget(Widget):
    def __init__(self, **kwargs):
        super(MyWidget, self).__init__(**kwargs)
        self.bind(size=self.on_size)

    def on_size(self, *args):
        print("当前小部件尺寸：", self.size)

from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button

class MyWidget(BoxLayout):
    def __init__(self, **kwargs):
        super(MyWidget, self).__init__(**kwargs)
        self.orientation = 'vertical'
        self.add_widget(Button(text='按钮', size_hint=(1, 1), on_release=self.on_button_release))

    def on_button_release(self, button):
        print("按钮尺寸：", button.size)