如何在Kivy/KivyMD中调用自定义函数，点击按钮时报NameError怎么解决？

开发者阿泽

2026-10-11

问题根因

KV语言的执行作用域无法直接访问Python全局空间定义的函数，仅能调用当前控件方法、所属页面（root）方法、或者App实例的方法
你写的全局verified_Login函数内部引用的root变量没有明确指向，就算函数能被调用也会触发二次报错
代码中额外创建的sm ScreenManager实例没有实际使用，运行时生效的是KV字符串里定义的ScreenManager

修复后完整代码

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

txtuser = 'Root'

screen_helper = """
ScreenManager:
    LoginScreen:
    ProfileScreen:


<LoginScreen>:
    name: 'login'
    MDRectangleFlatButton:
        text: 'Profile'
        pos_hint: {'center_x':0.5,'center_y':0.5}
        on_press: app.verified_Login()
<ProfileScreen>:
    name: 'profile'
    MDLabel:
        text: 'Test'
        halign: 'center'

    MDRectangleFlatButton:
        text: 'Back'
        pos_hint: {'center_x':0.5,'center_y':0.2}
        on_press: root.manager.current = 'login'

"""

class LoginScreen(Screen):
    pass

class ProfileScreen(Screen):
    pass

class DemoApp(MDApp):
    def verified_Login(self):
        if txtuser == 'Root':
            # self.root就是KV里定义的ScreenManager实例
            self.root.current = 'profile'
        else:
            print("oi")

    def build(self):
        screen = Builder.load_string(screen_helper)
        return screen

DemoApp().run()