如何在kivy中动态创建屏幕内的布局？

Question

我写了这个python代码，以在屏幕内以线形方式创建BoxLayout。

from kivy.uix.screenmanager import ScreenManager, Screen 
from kivy.app import App 
from kivy.uix.boxlayout import BoxLayout 
from kivy.uix.button import Button 

class ListScreen(Screen): 
    def __init__(self,**kwargs): 
     super(ListScreen, self).__init__(**kwargs)   
     layout = BoxLayout(orientation ='vertical') 
     top_buttons=BoxLayout() 
     layout.add_widget(top_buttons) 
     top_buttons.add_widget(Button(text='Save')) 

class ExampleApp(App): 
    def build(self):  
     root=ScreenManager() 
     root.add_widget(ListScreen(name='list')) 
     return root 


ExampleApp().run() 

它没有任何编译错误，但输出只是一个空白的屏幕运行。

Answer 1

的问题是，你还没有加入layout到ListScreen实例：

from kivy.uix.screenmanager import ScreenManager, Screen 
from kivy.app import App 
from kivy.uix.boxlayout import BoxLayout 
from kivy.uix.button import Button 

class ListScreen(Screen): 
    def __init__(self,**kwargs): 
     super(ListScreen, self).__init__(**kwargs)   
     layout = BoxLayout(orientation ='vertical') 
     self.add_widget(layout)       #<<<<<<<<<<<<<<<<< 
     top_buttons=BoxLayout() 
     layout.add_widget(top_buttons) 
     layout.add_widget(Button(text='Save')) 

class ExampleApp(App): 
    def build(self):  
     root=ListScreen() 
     root.add_widget(ListScreen(name='list')) 
     return root 


ExampleApp().run()