kivyMd 多屏

Question

我想使用 KivyMD 和 ScreenManager 创建一个登录和注销页面。但是它不断出错。 在 KivyMD 的文档中，仅显示了如何使用应用程序类创建它。但是，我的目标是使用屏幕管理器来管理两个屏幕登录和注销，功能是当我按下登录时，它应该进入注销页面并在第二个屏幕上显示电子邮件和密码。当我按下注销时，它应该返回登录屏幕。但它是抛出运行时

typeerro

error:
 
Traceback (most recent call last):
   File "f:\PycharmProjects\kivyProject1\login_form.py", line 101, in <module>
     MOgggg().run()
   File "C:\Users\User\anaconda3\lib\site-packages\kivy\app.py", line 955, in run
     self._run_prepare()
   File "C:\Users\User\anaconda3\lib\site-packages\kivy\app.py", line 925, in _run_prepare
     root = self.build()
   File "f:\PycharmProjects\kivyProject1\login_form.py", line 90, in build
     kk=Builder.load_string(KV)
   File "C:\Users\User\anaconda3\lib\site-packages\kivy\lang\builder.py", line 372, in load_string
     parser = Parser(content=string, filename=fn)
   File "C:\Users\User\anaconda3\lib\site-packages\kivy\lang\parser.py", line 483, in __init__
     self.parse(content)
   File "C:\Users\User\anaconda3\lib\site-packages\kivy\lang\parser.py", line 593, in parse
     objects, remaining_lines = self.parse_level(0, lines)
   File "C:\Users\User\anaconda3\lib\site-packages\kivy\lang\parser.py", line 696, in parse_level
     _objects, _lines = self.parse_level(
   File "C:\Users\User\anaconda3\lib\site-packages\kivy\lang\parser.py", line 696, in parse_level
     _objects, _lines = self.parse_level(
   File "C:\Users\User\anaconda3\lib\site-packages\kivy\lang\parser.py", line 756, in parse_level
     if current_property[:3] == 'on_':
   TypeError: 'NoneType' object is not subscriptable

from kivy.lang import Builder
from kivymd.app import MDApp
# from kivymd.uix.screen import Screen
from kivy.uix.screenmanager import Screen,ScreenManager
from kivymd.uix.button import MDRaisedButton
from kivymd.uix.textfield import MDTextField
from kivymd.uix.label import MDLabel
from kivy.config import Config

#set window size
Config.set('graphics', 'width', '800')
Config.set('graphics', 'height', '400')


KV="""
ScreenManager:
    LoginScreen:
    LogoutScreen:


<LoginScreen>:
    name: "login"
    MDBoxLayout:
        orientation:"vertical"
        padding: 180
        spacing: 10
        
        MDTextField:
            id: user_name
            hint_text:"Enter Username or Email"
            helper_text: "username must be unique"
            helper_text_mode:"on_focus"
            icon_left:"account"
            pos_hint:{"center_x":0.5,"center_y":0.5}
            size_hint:(None,None)
            width:300
        
        MDTextField:
            id: password
            hint_text:"Password [8-20 words]"
            helper_text: "Password must contain number, spacial char"
            helper_text_mode:"on_focus"
            icon_left:"lock-off"
            pos_hint:{"center_x":0.5,"center_y":0.5}
            size_hint:(None,None)
            width:300
            
        MDRaisedButton:
            text:"Login"
            pos_hint:{"center_x":0.5,"center_y":0.5}
            on_release:
                app.submit()
                app.root.current="logout"
                root.manager.transition.direction = "left"
                
<LogoutScreen>:
    name:"logout"
    BoxLayout:
        orientation: 'vertical'
        MDLabel:
                id: display_label
                text: ''
                theme_text_color: "Secondary"
                halign: 'center'
                font_style: "H6"
                size_hint_y: None
                height: self.texture_size[1]
        
        MDRaisedButton:
            text: "LogOut"
            pos_hint:{"center_x":0.5,"center_y":0.5}
            on_release:
                app.root.current="login"
                root.manager.transition.direction = "right"

"""
class LogoutScreen(Screen):
    pass

class LoginScreen(Screen):
    pass

class ScreenManager(ScreenManager):
    pass

class MOgggg(MDApp):
    
    
    def build(self):
        kk=Builder.load_string(KV)
        return kk

    def submit(self):
        email=self.root.ids.user_name.text
        paasswod=self.root.ids.password.text
        
        self.root.ids.display_label.text=f"Hi {email} , You'r successfully Login!\n and this is your passwrd: {paasswod}"
        
        print(email,paasswod)

MOgggg().run()

Answer 1

您收到的错误是由于

kv

字符串的格式错误造成的。在

LogoutScreen

的规则中，

MDLabel:

之后的缩进太多。

kv

语言对缩进非常敏感。只需更改：

    MDLabel:
            id: display_label
            text: ''
            theme_text_color: "Secondary"
            halign: 'center'
            font_style: "H6"
            size_hint_y: None
            height: self.texture_size[1]

至：

    MDLabel:
        id: display_label
        text: ''
        theme_text_color: "Secondary"
        halign: 'center'
        font_style: "H6"
        size_hint_y: None
        height: self.texture_size[1]