访问“高度"小部件实例的属性 [英] Accessing "height" property of an instance of a widget

问题描述

创建小部件后，我需要访问其高度.但是，每当我尝试访问my_widget.height时，它都会返回默认高度100而不是实际高度.

I need to access the height of a widget after it is created. However, whenever I tried to access my_widget.height, it returns the default height of 100 rather than the actual height.

可以在my_widget类的on_touch_down定义内检索self.height.

Retrieving self.height inside the on_touch_down definition of the my_widget class works though.

我的问题确实在以下代码中得到了最好的描述.

My problem is really best described in the following code.

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout


class Layout(BoxLayout):

    # the following yields the correct height of Layout,
    # which is the same as the height of the Window
    def on_touch_down(self, touch): 
        print("inside Layout via on_touch_down:", self.height)



class MyApp(App):
    def build(self):

        l = Layout()

        # However, accessing the height here yields the
        # the default height 100
        print("inside MyApp:", l.height)

        return l




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

我花了数小时阅读API文档的不同部分以及Kivy网站上的指南，但找不到我想念的东西.

I spent hours reading different parts of the API doc and the guides on the Kivy website, but couldn't quite find what I missed.

推荐答案

在build()方法中，尚未构建应用程序，因此小部件具有其默认值，因此您必须稍后获取该信息.有以下选项:

In the build() method the application has not yet been built so the widget has its default value, so you must obtain that information a moment later, for this there are the following options:

• 使用 App.on_start() :

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout


class Layout(BoxLayout):
    pass


class MyApp(App):
    def build(self):
        l = Layout()
        return l

    def on_start(self):
        print(self.root.height)


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

• 使用 Clock.schedule_once() :

from kivy.app import App
from kivy.clock import Clock
from kivy.uix.boxlayout import BoxLayout


class Layout(BoxLayout):
    pass


class MyApp(App):
    def build(self):
        l = Layout()
        Clock.schedule_once(self.after_build)
        return l

    def after_build(self, dt):
        print(self.root.height)


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

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