KivyMD - 下拉菜单：AttributeError: 'super' 对象在

如何解决KivyMD - 下拉菜单：AttributeError: 'super' 对象在

我被这个问题困扰了好几天。而且，现在，我对这种错误有了一点了解，它与尝试使用 kivy 字符串中的 id 访问元素（下拉菜单）的 python 文件有关。

但由于我是 OOP 的新手，我无法弄清楚到底需要做什么。

代码如下：

*代码中元素的排列稍后会有所改变。所以不用担心。

我需要的只是让下拉菜单在这种代码中工作（即，屏幕管理器中有多个屏幕，每个屏幕由一个单独的类表示。）

    from kivymd.app import MDApp
    from kivy.lang.builder import Builder
    from kivy.uix.screenmanager import ScreenManager,Screen
    from kivymd.uix.menu import MDDropdownMenu
    from kivymd.uix.datatables import MDDataTable
    from kivy.metrics import dp
    from kivymd.uix.button import MDFloatingActionButton
    
    
    class MenuScreen(Screen):
        pass
    
    
    class ProScreen(Screen):
        def __init__(self,**kwargs):
            super().__init__(**kwargs)
            
            menu_items = [{"text": f"{i}"} for i in ["XML","Bootstrap","Mysql","None"]]
            self.menu = MDDropdownMenu(
                                       caller=self.ids.drop_item,items=menu_items,width_mult=4,callback=self.set_item)   
            
            self.menu.bind(on_release=self.set_item)
                
        def set_item(self,instance_menu_item):
            self.ids.drop_item.text = instance_menu_item.text
            self.menu.dismiss()
            
        def display_selection(self):
            select1 = self.ids.drop_item.text                
            #lx = self.root.ids.lx.text
            #res = ["the dropdown menu selection is:",]
            print (select1)
        
        def on_pre_enter(self,*args):
            self.app.title = "Slab"
            
        def show_data(self,*args):
            ly = self.ids.ly.text                 
            #lx = self.root.ids.lx.text
            res = ["hi we are bts",float(ly)]
            print (res)
            res2 = float(ly)+1
            self.ids.res11.text = str(res)
            print (res2)
    
    class UploadScreen(Screen):
        pass
    
    
    class DemoApp18(MDApp):
    
        def __init__(self,**kwargs):
            super().__init__(**kwargs)
            self.theme_cls.primary_palette = "Blue"
            #self.scr22 = Builder.load_string(temp_kv.KV)
            self.screen_manager = Builder.load_string(screen_helper)
            
            self.screen_manager = ScreenManager()
            self.screen_manager.add_widget(MenuScreen(name='menupage'))
            self.screen_manager.add_widget(ProScreen(name='pro'))
            self.screen_manager.add_widget(UploadScreen(name='upload'))
            
        def build(self):
            return self.screen_manager
            
    
    DemoApp18().run()
    
    

而 Kivy 字符串被称为“screen_helper”，在下面分享：

"""
ScreenManager:
    MenuScreen:
    ProScreen:
    UploadScreen:
<MenuScreen>:
    name: 'menupage'
    MDRectangleFlatButton:
        text: 'Pro'
        pos_hint: {'center_x':0.5,'center_y':0.6}
        on_press: root.manager.current = 'pro'
    MDRectangleFlatButton:
        text: 'Upload'
        pos_hint: {'center_x':0.5,'center_y':0.5}
        on_press: root.manager.current = 'upload'
    
<ProScreen>:
    name: 'pro'
    MDLabel:
        text: 'Pro'
        halign: 'center'
        
    MDTextField:
        id: ly
        hint_text: "Enter longer span of slab"
        helper_text: "(should be in m)"
        helper_text_mode: "on_focus"
        icon_right: "android"
        icon_right_color: app.theme_cls.primary_color
        size_hint_x:None
        width:250
        halign: "center"
        valign: "top"
        
    MDRectangleFlatButton:
        text: 'Pro'
        pos_hint: {'center_x':0.2,'center_y':0.1}
        on_press: 
            #root.manager.current = 'menupage'
            #app.screen_manager.pro.show_data()
            root.show_data()
            
    MDLabel:
        #text: "Enter details:"
        theme_font_styles: "H1"
        id: res11
        #halign: "center"
        
    MDDropDownItem:
        id: drop_item
        pos_hint: {'center_x': .5,'center_y': .5}
        text: 'Select OPtion'
        on_release: app.menu.open()
        
    MDRaisedButton:
        id: btn1
        text: "Display"
        md_bg_color: app.theme_cls.primary_color
        pos_hint: {"center_x": .5,"center_y": .75}
        on_release: 
            root.display_selection()
        
    MDRectangleFlatButton:
        text: 'Back'
        pos_hint: {'center_x':0.5,'center_y':0.1}
        on_press: root.manager.current = 'menupage'

<UploadScreen>:
    name: 'upload'
    MDLabel:
        text: 'Upload'
        halign: 'center'
    MDRectangleFlatButton:
        text: 'Back'
        pos_hint: {'center_x':0.5,'center_y':0.1}
        on_press: root.manager.current = 'menupage'
        
"""

DropDownMenu 是我正在创建的内容的重要组成部分。我什至不能用其他元素替换它。 请建议我任何方法来完成这项工作

哦！并且错误消息如下所示：

Traceback (most recent call last):

  File "kivy\properties.pyx",line 860,in kivy.properties.ObservableDict.__getattr__

KeyError: 'drop_item'


During handling of the above exception,another exception occurred:

Traceback (most recent call last):

  File "C:\Users\kmd_inpython2.py",line 212,in <module>
    DemoApp18().run()

  File "C:\Users\kmd_inpython2.py",line 196,in __init__
    self.screen_manager = Builder.load_string(screen_helper)

  File "C:\Users\builder.py",line 405,in load_string
    rule_children=rule_children)

  File "C:\Users\builder.py",line 654,in _apply_rule
    child = cls(__no_builder=True)

  File "C:\Users\kmd_inpython2.py",line 115,in __init__
    caller=self.ids.drop_item,File "kivy\properties.pyx",line 863,in kivy.properties.ObservableDict.__getattr__

AttributeError: 'super' object has no attribute '__getattr__'