有关kivy.ui.widget.WidgetException的问题

Question

我是python和kivymd的新手，我正在尝试开发一个数据输入程序。但是，当我为一个选择创建下拉菜单时，出现了一个错误，在我选择一个项目后，我无法更新文本字段的值。以下是python代码：

from kivymd.app import MDApp
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.properties import ObjectProperty
from kivy.lang import Builder
from kivy.clock import Clock
from kivy.properties import ObjectProperty
from kivymd.uix.menu import MDDropdownMenu
class AMRMenu(Screen):
def GIbutton(self):
sm.current = 'GI'
class GIWindow(Screen):
weather = ObjectProperty(None)
menu_weather_items = [{"text":"Sunny"},{"text":"Cloudy"},{"text":"Raining"}]
menu_FeedResponse_items=[{"text":"High"},{"text":"Medium"},{"text":"Low"}]
def __init__(self, **kwargs):
super().__init__(**kwargs)
self.menu = MDDropdownMenu(
items=self.menu_weather_items, 
width_mult=4,
caller = self.weather,
callback=self.set_item)
def set_item(self, instance):
def set_item(interval):
self.weather.text = instance.text
self.menu.dismiss()
Clock.schedule_once(set_item, 0.5) 
class WindowManager(ScreenManager):
pass
sm = WindowManager()    
class MainApp(MDApp):   
def __init__(self, **kwargs):
super().__init__(**kwargs)
kv = Builder.load_file("FR.kv")
def build(self):        
screens = [AMRMenu(name = "menu"), GIWindow(name = "GI")]
for screen in screens:
sm.add_widget(screen)
sm.current = "menu"
return sm
if __name__ == "__main__":
MainApp().run()

这是kv.文件：

<AMRMenu>:
name:"menu"
BoxLayout:
orientation: "vertical"
MDToolbar:
title: "Main Menu"
MDList:
OneLineListItem:
text: "General Information"
on_press: root.GIbutton()
OneLineListItem:
text: "Water Temperature"
OneLineListItem
text: "Feeding Amount"
OneLineListItem: 
text: "Residue and Feeding response"
OneLineListItem: 
text: "Dead fish"
OneLineListItem:
text: "Sell/Use"
<GIWindow>
name: "GI"
weather: weather
ScrollView:
id: screen
MDBoxLayout:
orientation: 'vertical'
adaptive_height: True
MDTextField:
id: weather
pos_hint: {'center_x': .5, 'center_y': .5}
hint_text: "Weather"
icon_right: "arrow-down-drop-circle-outline"
input_filter: lambda text, from_undo: text[:5 - len(self.text)]
on_focus: root.menu.open()

这是错误消息：

File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/kivy/core/window/__init__.py", line 1297, in add_widget
(widget, widget.parent)
kivy.uix.widget.WidgetException: Cannot add <kivymd.uix.menu.MDDropdownMenu object at 0x7fd2fa31a6e0> to window, it already has a parent <kivy.core.window.window_sdl2.WindowSDL object at 0x7fd2f65826e0>

我不知道为什么会发生这种事。如果有人弄清楚了，那会有很大帮助。感谢您阅读此问题

Answer 1

问题是您的kv行：

on_focus: root.menu.open()

每次focus更改时都打开菜单。因此，即使focus变为false，它也会尝试打开菜单。一个简单的解决方案是当focus is为True时只打开菜单`：

on_focus: if self.focus: root.menu.open()