Kivy：Pythonで追加されたウィジェット内で親を取得

Question

kvlangによって追加されていないがPythonでウィジェット内の親への参照を取得するにはどうすればよいですか？ 通常、self.parentを呼び出すだけですが、ウィジェットがPythonで親に追加された場合はNullが返されます。

例：

import kivy 
kivy.require('1.9.0') # replace with your current kivy version ! 

from kivy.app import App 
from kivy.lang import Builder 
from kivy.uix.screenmanager import ScreenManager,Screen 
from kivy.clock import Clock 

kvlang = ''' 
<ScreenManagement>: 
    ScreenOne: 

<ScreenOne>: 
    name: 'First' 


<ScreenTwo>: 
    name: 'Second' 

''' 


class ScreenManagement(ScreenManager): 
    def __init__(self,**kwargs): 
     super().__init__(**kwargs) 

     def setup(*args): 
      self.add_widget(ScreenTwo()) #add ScreenTwo later in python 

     Clock.schedule_once(setup) 

class ScreenOne(Screen): 
    def __init__(self,**kwargs): 
     super().__init__() 

     def setup(*args): 
      print("Parent of ScreenOne: {}".format(self.parent))  #this is working 
     Clock.schedule_once(setup) 

class ScreenTwo(Screen): 
    def __init__(self,**kwargs): 
     super().__init__() 

     def setup(*args): 
      print("Parent of ScreenTwo: {}".format(self.parent))  #this is not working, self.parent will return None 
     Clock.schedule_once(setup) 



class MyApp(App): 

    def build(self): 
     Builder.load_string(kvlang) 
     return ScreenManagement() 


if __name__ == '__main__': 
    MyApp().run() 

これが返されます：

Parent of ScreenOne: <__main__.ScreenManagement object at 0x7f98a3fddb40> 
Parent of ScreenTwo: None 

Answer 1

ウィジェットはadd_widgetで追加は、実際に彼らの親への有効な参照を持っています

from kivy.app import App 
from kivy.uix.screenmanager import ScreenManager, Screen 

from kivy.lang import Builder 
Builder.load_string(''' 
<ScreenTwo> 
    Label: 
     text: 'Hello, world'  
''') 

class ScreenManagement(ScreenManager): 
    def __init__(self,**kwargs): 
     super(ScreenManagement, self).__init__(**kwargs) 
     screen = ScreenTwo() 

     print(screen.parent) 
     self.add_widget(screen) 
     print(screen.parent) 


class ScreenTwo(Screen): 
    def on_touch_down(self, *args): 
     print(self.parent) 


class MyApp(App): 
    def build(self): 
     return ScreenManagement() 


if __name__ == '__main__': 
    MyApp().run() 

それはちょうどでは使用できませんその__init__メソッド。