KivyMD点击MDTopAppBar菜单报错：name 'navigation_draw' is not defined

问题原因 #

报错NameError: name 'navigation_draw' is not defined是因为在kv字符串中，lambda函数无法直接访问MobileApp类里的navigation_draw方法。在Kivy的kv语言中，需要通过app关键字来引用当前应用实例的方法。

修正方案 #

将kv字符串中left_action_items里的lambda x: navigation_draw()改为lambda x: app.navigation_draw()即可解决问题。

修正后的完整代码 #

from kivymd.app import MDApp
from kivy.lang import Builder
from kivy.core.window import Window
Window.size=(700,700)
screen_helper ="""
Screen:
     BoxLayout:
          orientation:'vertical'
          MDTopAppBar:
               title:'My First App'
               left_action_items:[['menu',lambda x: app.navigation_draw()]]
          MDLabel:
               text:'hello App'
               halign:'center'
"""
class MobileApp(MDApp):
    def build(self):
        screen = Builder.load_string(screen_helper)
        return screen

    def navigation_draw(self):
        print("Navigation")

MobileApp().run()

内容的提问来源于stack exchange，提问作者data science