將小部件結果添加到「AttributeError：'HomeScreen'對象沒有屬性'_trigger_layout'」

Question

爲什麼此代碼會生成以下錯誤？

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

因爲已覆蓋init方法，這是必要的。在下面的代碼中，我也覆蓋了init方法，但我也在覆蓋之前調用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()