在kivy上添加新按钮和屏幕时出错

Question

My python file is

from kivy.app import App
from kivy.lang import Builder 
from kivy.uix.screenmanager import ScreenManager, Screen, FadeTransition
from kivy.uix.widget import Widget
from kivy.graphics import Line


class MainScreen(Screen):
    pass
class TaskScreen(Screen):
    pass
class DefrostScreen(Screen):
    pass
class ScreenManagement(ScreenManager):
    pass
presentation = Builder.load_file("main3.kv")

class MainApp(App):
    def build(self):
        return presentation

if __name__ == "__main__":
    MainApp().run()

my kv file is

#: import FadeTransition kivy.uix.screenmanager.FadeTransition

ScreenManagement:
    transition: FadeTransition()
    MainScreen:
    TaskScreen:
    DefrostScreen:

<MainScreen>:
    name:"main"
    Button:
        on_release: app.root.current = "Tasks"
        text: "Tasks"
        font_size: 25
        size_hint:0.3,0.2
        pos_hint:{"left":1,"top":1}
    Button:
        on_release: app.root.current = "Defrost"
        text: "defrost"
        font_size: 25
        size_hint:0.3,0.2
        pos_hint:{"left":1,"top":0.8}

<TaskScreen>:
    name: "Tasks"
    FloatLayout:
        Button:
            color: 0,1,0,1
            font_size: 25
            size_hint: 0.3,0.2
            text: "back home"
            on_release: app.root.current = "main"
            pos_hint: {"right":1, "top":1}
<DefrostScreen>:
    name: "Defrost"
        Button:
            color: 0,1,0,1
            font_size: 25
            size_hint: 0.3,0.2
            text: "back home"
            on_release: app.root.current = "main"
            pos_hint: {"right":1, "top":1}

and the error when I run my python file is

Traceback (most recent call last):
   File "main3.py", line 16, in <module>
     presentation = Builder.load_file("main3.kv")
   File "C:\python34\lib\site-packages\kivy\lang.py", line 1842, in load_file
     return self.load_string(data, **kwargs)
   File "C:\python34\lib\site-packages\kivy\lang.py", line 1889, in load_string
     parser = Parser(content=string, filename=fn)
   File "C:\python34\lib\site-packages\kivy\lang.py", line 1264, in __init__
     self.parse(content)
   File "C:\python34\lib\site-packages\kivy\lang.py", line 1366, in parse
     objects, remaining_lines = self.parse_level(0, lines)
   File "C:\python34\lib\site-packages\kivy\lang.py", line 1529, in parse_level
     if current_property[:3] == 'on_':
 TypeError: 'NoneType' object is not subscriptable
Press any key to continue . . .

It worked when I used sentdex's tutorial but I wanted to adapt it so i could use it and now it comes up with this error

send help please

Answer 1

你有错误的缩进 - name: "Defrost"和Button:应该有相同的缩进。