Kivy Builder.load_file() 没有按预期工作答案

【问题标题】：Kivy Builder.load_file() not working as expectedKivy Builder.load_file() 没有按预期工作
【发布时间】：2019-12-31 16:17:17
【问题描述】：

我正在尝试运行一个小型 kivy 应用程序。当我使用 Builder.load_string() 时，我的应用程序运行正常，当我使用 Builder.load_file() 时，我得到的只是一个空白屏幕。这是我的代码

main.py - 使用 Builder.load_string()

from kivy.lang import Builder
from kivymd.app import MDApp
from kivymd.uix.chip import MDChip
from kivy.uix.screenmanager import ScreenManager, Screen


Builder.load_string("""
<MenuScreen>:
    BoxLayout:
        Button:
            text: 'Goto settings'
            on_press:
                root.manager.transition.direction = 'left'
                root.manager.current = 'settings'
        Button:
            text: 'Quit'

<SettingsScreen>:
    BoxLayout:
        Button:
            text: 'My settings button'
        Button:
            text: 'Back to menu'
            on_press:
                root.manager.transition.direction = 'right'
                root.manager.current = 'menu'
""")


class MenuScreen(Screen):
    pass


class SettingsScreen(Screen):
    pass


sm = ScreenManager()
sm.add_widget(MenuScreen(name='menu'))
sm.add_widget(SettingsScreen(name='settings'))


class MyWidget(MDChip):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)


class MainApp(MDApp):
    def __init__(self, **kwargs):
        self.title = "My Material Application"
        super().__init__(**kwargs)

    def build(self):
        return sm


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

这是与 Builder.load_file() 相同的代码

main.py

from kivy.lang import Builder
from kivymd.app import MDApp
from kivymd.uix.chip import MDChip
from kivy.uix.screenmanager import ScreenManager, Screen


class MenuScreen(Screen):
    pass


class SettingsScreen(Screen):
    pass


sm = ScreenManager()
sm.add_widget(MenuScreen(name='menu'))
sm.add_widget(SettingsScreen(name='settings'))


class MyWidget(MDChip):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)


class MainApp(MDApp):
    def __init__(self, **kwargs):
        self.title = "My Material Application"
        super().__init__(**kwargs)

    def build(self):
        self.root = Builder.load_file('main.kv')
        return sm


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

main.kv

<MenuScreen>:
    BoxLayout:
        Button:
            text: 'Goto settings'
            on_press:
                root.manager.transition.direction = 'left'
                root.manager.current = 'settings'
        Button:
            text: 'Quit'

<SettingsScreen>:
    BoxLayout:
        Button:
            text: 'My settings button'
        Button:
            text: 'Back to menu'
            on_press:
                root.manager.transition.direction = 'right'
                root.manager.current = 'menu'

我运行代码时得到的只是一个空白屏幕。

我做错了什么？

【问题讨论】：

标签： python-3.x kivy kivy-language

【解决方案1】：

显然你必须在 def build(self) 中包含以下代码

sm = ScreenManager()
sm.add_widget(MenuScreen(name='menu'))
sm.add_widget(SettingsScreen(name='settings'))

所以最终的 main.py 文件将是

from kivy.lang import Builder
from kivymd.app import MDApp
from kivymd.uix.chip import MDChip
from kivy.uix.screenmanager import ScreenManager, Screen


class MenuScreen(Screen):
    pass


class SettingsScreen(Screen):
    pass


class MyWidget(MDChip):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)


class MainApp(MDApp):
    def __init__(self, **kwargs):
        self.title = "My Material Application"
        super().__init__(**kwargs)

    def build(self):
        self.root = Builder.load_file('main.kv')
        sm = ScreenManager()
        sm.add_widget(MenuScreen(name='menu'))
        sm.add_widget(SettingsScreen(name='settings'))
        return sm


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

【讨论】：