Kivy 无法在屏幕上放置按钮答案

【问题标题】：Kivy unable to place button on screenKivy 无法在屏幕上放置按钮
【发布时间】：2020-10-01 13:07:33
【问题描述】：

我似乎无法在屏幕上放置按钮。这是我的代码：

from kivymd.app import MDApp
from kivymd.uix.screen import Screen
from kivy.lang import Builder
from kivymd.uix.button import MDRectangleFlatButton
from helpers import  username_helper, password_helper

class Demoapp(MDApp):
    def build(self):
        self.theme_cls.primary_palette='Cyan'
        self.theme_cls.primary_hue = 'A700'

        button_sing = MDRectangleFlatButton(text='food', pos_hint={"center_x": 0.5,
                         "center_y":0.5}) 
     
        screen = Screen()
        username = Builder.load_string(username_helper)
        password = Builder.load_string(password_helper)
        screen.add_widget(username)
        screen.add_widget(password)
        screen.add_widget(button_sing)
        #screen.add_widget(button_singup)
        return screen

if __name__ == '__main__':
    Demoapp().run()

但是我收到了这个错误：

 line 12, in build
     button_sing = MDRectangleFlatButton(text='food', pos_hint={"center_x": 0.5, "center_y": 0.5})
   File "kivy\_event.pyx", line 195, in kivy._event.EventDispatcher.__cinit__
   File "kivy\properties.pyx", line 1316, in kivy.properties.ReferenceListProperty.link_deps
   File "kivy\properties.pyx", line 464, in kivy.properties.Property.fbind
 KeyError: ''

【问题讨论】：

我想在窗口中唱歌，当我尝试在屏幕上添加按钮时，它一直给我这个错误

标签： python canvas kivy line

【解决方案1】：

从命令行一一安装：

pip install --upgrade pip wheel setuptools
pip install docutils pygments pypiwin32 kivy.deps.sdl2 kivy.deps.glew
pip install kivy.deps.gstreamer
pip install kivy.deps.angle
pip install kivy

【讨论】：

【解决方案2】：

我多次尝试解决这个问题。问题只是如此简单，你需要切换这两行。

button_sing = MDRectangleFlatButton(text='food', pos_hint={"center_x": 0.5,
                             "center_y":0.5}) 
screen = Screen()

完成了

【讨论】：