将小部件结果添加到“AttributeError：'HomeScreen'对象没有属性'_trigger_layout'”

Question

为什么此代码会生成以下错误？

AttributeError: 'HomeScreen' object has no attribute '_trigger_layout'

class HomeScreen(BoxLayout): 

    def __init__(self): 

     print "homescreen" 

     topbar = BoxLayout(spacing = -2, size = (64, 64), size_hint = (1, None)) 

     back_button = Button(size = (32, 64), size_hint = (None, 1), text = '>', font_size = 15 + 0.015 * self.height, background_color = (0.239, 0.815, 0.552, 1)) 
     home_button = Button(text = "HOME", font_size = 10 + 0.015 * self.width, background_color = (0.239, 0.815, 0.552, 1)) 
     more_button = Button(size = (32, 64), size_hint = (None, 1), text = '...', font_size = 15 + 0.015 * self.height, background_color = (0.239, 0.815, 0.552, 1)) 

     topbar.add_widget(back_button) 
     topbar.add_widget(home_button) 
     topbar.add_widget(more_button) 

     self.add_widget(topbar) 

Answer 1

因为已覆盖init方法，这是必要的。在下面的代码中，我也覆盖了init方法，但我也在覆盖之前调用init方法。

class HomeScreen(BoxLayout): 
    def __init__(self, **kwargs): 
     super(HomeScreen, self).__init__(**kwargs) 
     ... 

---

from kivy.app import App 
from kivy.uix.slider import Slider 
from kivy.uix.treeview import TreeView, TreeViewNode 
from kivy.uix.button import Button 
from kivy.uix.slider import Slider 
from kivy.uix.label import Label 
from kivy.uix.boxlayout import BoxLayout 
from kivy.lang import Builder 

class HomeScreen(BoxLayout): 
    def __init__(self, **kwargs): 
     super(HomeScreen, self).__init__(**kwargs) 


     print("homescreen") 

     topbar = BoxLayout(spacing = 0, size = (64, 64), size_hint = (1, None)) 

     back_button = Button(size = (32, 64), size_hint = (None, 1), text = '>', font_size = 15 + 0.015 * self.height, background_color = (0.239, 0.815, 0.552, 1)) 
     home_button = Button(text = "HOME", font_size = 10 + 0.015 * self.width, background_color = (0.239, 0.815, 0.552, 1)) 
     more_button = Button(size = (32, 64), size_hint = (None, 1), text = '...', font_size = 15 + 0.015 * self.height, background_color = (0.239, 0.815, 0.552, 1)) 

     topbar.add_widget(back_button) 
     topbar.add_widget(home_button) 
     topbar.add_widget(more_button) 
     self.add_widget(topbar) 


class TestApp(App): 
    def build(self): 
     return HomeScreen() 

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