Python Kivy AttributeError: 'NoneType' 對象沒有屬性 'bind'

Question

我正在嘗試用 Kivy 編寫一個計算器 GUI。

這是代碼：

實驗.py

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.properties import ListProperty, NumericProperty, BooleanProperty, StringProperty
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.lang import Builder 

import calculator_calc




Builder.load_file("calculatorgui.kv")



class CalculatorScreen1(Screen):
    pass

class CalculatorScreen2(Screen):
    pass



class CalculatorModeIndicator(BoxLayout):
    pass

class CalculatorMonitor1(BoxLayout):
    pass

class CalculatorButtons(BoxLayout):
    pass





screen_manager = ScreenManager()

screen_manager.add_widget(CalculatorScreen1(name = "screen1"))
screen_manager.add_widget(CalculatorScreen2(name = "screen2"))



class Calculator(App):
    expression_tokens = ListProperty([])
    expression_value = StringProperty("")
    angle_mode = StringProperty("degrees")
    angle_mode_text = StringProperty("D")
    button_mode = NumericProperty(1)
    button_mode_text = StringProperty("1ST")
    store_mode = BooleanProperty(False)


    def build(self):
        return screen_manager


    def switch_screen(self, screen):
        screen_manager.current = screen

    def set_button_mode(self, button_mode):
        self.button_mode = button_mode

        if button_mode == 1:
            self.button_mode_text = "1ST"
        elif button_mode == 2:
            self.button_mode_text = "2ND"
        elif button_mode == 3:
            self.button_mode_text = "3RD"  

    def set_angle_mode(self, angle_mode):
        calculator_calc.evaluate(f"angle_mode {angle_mode}") 

        self.angle_mode = angle_mode

        if angle_mode == "degrees":
            self.angle_mode_text = "D"
        elif angle_mode == "radians":
            self.angle_mode_text = "R"
        elif angle_mode == "gradians":
            self.angle_mode_text = "G"  

    def add_token(self, token):
        self.expression_tokens.append(token)

    def calculate(self, expression):
        result = calculator_calc.evaluate(expression)
        self.expression_value = str(result)
        calculator_calc.evaluate(f"ANS = {result}")


Calculator().run()

計算器gui.kv

#:kivy 1.11.1


<CalculatorScreen1>:
    BoxLayout:
        orientation: "vertical"

        CalculatorModeIndicator:

        CalculatorMonitor1:

        CalculatorButtons:


<CalculatorScreen2>:
    BoxLayout:
        orientation: "vertical"

        Label:
            text: "This is Screen 2"

        Button:
            text: "Screen2"
            on_press: app.switch_screen("screen1")


<CalculatorModeIndicator>:
    Label:
        size_hint_x: None
        width: "30dp"
        text: app.button_mode_text

    Label:
        size_hint_x: None
        width: "30dp"
        text: app.angle_mode_text


<CalculatorMonitor1>:    
    orientation: "vertical"

    Label:
        size_hint_y: None
        height: "30dp"
        text_size: self.size
        halign: "left"
        valign: "top"
        text: '"".join(app.expression_tokens)'

    Label:
        size_hint_y: None
        height: "30dp"
        text_size: self.size
        halign: "right"
        valign: "bottom"
        text: 'app.expression_value'


<CalculatorButtons>:    
    orientation: "vertical"

    BoxLayout: 
        Button:
            text: "1ST"
            on_press: app.set_button_mode(1)

        Button:
            text: "2ND"
            on_press: app.set_button_mode(2)

        Button:
            text: "3RD"
            on_press: app.set_button_mode(3)

    BoxLayout:
        Button:
            text: "DEGREES"
            on_press: 
                app.set_angle_mode("degrees")
        Button:
            text: "RADIANS"
            on_press: 
                app.set_angle_mode("radians")
        Button:
            text: "GRADIANS"
            on_press:
                app.set_angle_mode("gradians")

    BoxLayout:
        Button:
            text: "A"
            on_press: app.add_token(self.text) if not app.store_mode else app.store("A")
        Button:
            text: "B"
            on_press: app.add_token(self.text) if not app.store_mode else app.store("B")
        Button:
            text: "C"
            on_press: app.add_token(self.text) if not app.store_mode else app.store("C")
        Button:
            text: "D"
            on_press: app.add_token(self.text) if not app.store_mode else app.store("D")
        Button:
            text: "E"
            on_press: app.add_token(self.text) if not app.store_mode else app.store("E")

    # BoxLayout:
    #     Button:
    #         text: "sin" if app.button_mode == 1 else "asin" if app.button_mode == 2 else "sinh"
    #         on_press: app.add_token(f"{self.text}(")
    #     Button:
    #         text: "cos" if app.button_mode == 1 else "acos" if app.button_mode == 2 else "cosh"
    #         on_press: app.add_token(f"{self.text}(")
    #     Button:
    #         text: "tan" if app.button_mode == 1 else "atan" if app.button_mode == 2 else "tanh"
    #         on_press: app.add_token(f"{self.text}(")
    #     Button:
    #         text: "log"
    #         on_press: app.add_token(self.text + "(")
    #     Button:
    #         text: "ln"
    #         on_press: app.add_token(self.text + "(")

    BoxLayout:
        Button:
            text: "("
            on_press: app.add_token(self.text)
        Button:
            text: ")"
            on_press: app.add_token(self.text)
        Button:
            text: "STO"
            on_press: app.store_mode = True
        Button:
            text: "swt"
            on_press: app.switch_screen("screen2")
        Button:
            text: ","
            on_press: app.add_token(self.text)

    BoxLayout:
        Button:
            text: "7"
            on_press: app.add_token(self.text)
        Button:
            text: "8"
            on_press: app.add_token(self.text)
        Button:
            text: "9"
            on_press: app.add_token(self.text)
        Button:
            text: "DEL"
            on_press: app.expression_tokens = app.expression_tokens[:-1]
        Button:
            text: "AC"
            on_press: 
                app.expression_tokens = []

    BoxLayout:
        Button:
            text: "4"
            on_press: app.add_token(self.text)
        Button:
            text: "5"
            on_press: app.add_token(self.text)
        Button:
            text: "6"
            on_press: app.add_token(self.text)
        Button:
            text: "*"
            on_press: app.add_token(self.text)
        Button:
            text: "/"
            on_press: app.add_token(self.text)

    BoxLayout:
        Button:
            text: "1"
            on_press: app.add_token(self.text)
        Button:
            text: "2"
            on_press: app.add_token(self.text)
        Button:
            text: "3"
            on_press: app.add_token(self.text)
        Button:
            text: "+"
            on_press: app.add_token(self.text)
        Button:
            text: "-"
            on_press: app.add_token(self.text)

    BoxLayout:
        Button:
            text: "0"
            on_press: app.add_token(self.text)
        Button:
            text: "000"
            on_press: app.add_token(self.text)
        Button:
            text: "."
            on_press: app.add_token(self.text)
        Button:
            text: "ANS"
            on_press: app.add_token(self.text)
        Button:
            text: "="
            on_press: app.calculate("".join(app.expression_tokens))

當我嘗試運行腳本時，我的控制台返回此錯誤消息：

(venv) C:\Users\Wendelin\Documents\Programming\calculation>c:/Users/Wendelin/Documents/Programming/calculation/venv/Scripts/python.exe c:/Users/Wendelin/Documents/Programming/calculation/Calculator/experiment.py
[INFO   ] [Logger      ] Record log in C:\Users\Wendelin\.kivy\logs\kivy_19-12-19_29.txt
[INFO   ] [deps        ] Successfully imported "kivy_deps.gstreamer" 0.1.17
[INFO   ] [deps        ] Successfully imported "kivy_deps.glew" 0.1.12
[INFO   ] [deps        ] Successfully imported "kivy_deps.sdl2" 0.1.22
[INFO   ] [Kivy        ] v1.11.1
[INFO   ] [Kivy        ] Installed at "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\__init__.py"
[INFO   ] [Python      ] v3.7.5 (tags/v3.7.5:5c02a39a0b, Oct 15 2019, 00:11:34) [MSC v.1916 64 bit (AMD64)]
[INFO   ] [Python      ] Interpreter at "c:\Users\Wendelin\Documents\Programming\calculation\venv\Scripts\python.exe"
[INFO   ] [Factory     ] 184 symbols loaded
[INFO   ] [Image       ] Providers: img_tex, img_dds, img_sdl2, img_pil, img_gif (img_ffpyplayer ignored)
[INFO   ] [Window      ] Provider: sdl2
[INFO   ] [GL          ] Using the "OpenGL" graphics system
[INFO   ] [GL          ] GLEW initialization succeeded
[INFO   ] [GL          ] Backend used <glew>
[INFO   ] [GL          ] OpenGL version <b'4.4.0 - Build 20.19.15.4463'>
[INFO   ] [GL          ] OpenGL vendor <b'Intel'>
[INFO   ] [GL          ] OpenGL renderer <b'Intel(R) Iris(TM) Graphics 540'>
[INFO   ] [GL          ] OpenGL parsed version: 4, 4
[INFO   ] [GL          ] Shading version <b'4.40 - Build 20.19.15.4463'>
[INFO   ] [GL          ] Texture max size <16384>
[INFO   ] [GL          ] Texture max units <32>
[INFO   ] [Window      ] auto add sdl2 input provider
[INFO   ] [Window      ] virtual keyboard not allowed, single mode, not docked
[INFO   ] [Text        ] Provider: sdl2
 Traceback (most recent call last):
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\builder.py", line 249, in create_handler
     return eval(value, idmap), bound_list
   File "c:\Users\Wendelin\Documents\Programming\calculation\Calculator\calculatorgui.kv", line 38, in <module>
     text: app.angle_mode_text
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\parser.py", line 75, in __getattribute__
     object.__getattribute__(self, '_ensure_app')()
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\parser.py", line 70, in _ensure_app    
     app.bind(on_stop=lambda instance:
 AttributeError: 'NoneType' object has no attribute 'bind'

 During handling of the above exception, another exception occurred:

 Traceback (most recent call last):
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\builder.py", line 692, in _apply_rule  
     rctx['ids'])
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\builder.py", line 254, in create_handler
     cause=tb)
 kivy.lang.builder.BuilderException: Parser: File "c:\Users\Wendelin\Documents\Programming\calculation\Calculator\calculatorgui.kv", 
line 38:
 ...
      36:        size_hint_x: None
      37:        width: "30dp"
 >>   38:        text: app.angle_mode_text
      39:
      40:
 ...
 AttributeError: 'NoneType' object has no attribute 'bind'
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\builder.py", line 249, in create_handler
     return eval(value, idmap), bound_list
   File "c:\Users\Wendelin\Documents\Programming\calculation\Calculator\calculatorgui.kv", line 38, in <module>
     text: app.angle_mode_text
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\parser.py", line 75, in __getattribute__
     object.__getattribute__(self, '_ensure_app')()
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\parser.py", line 70, in _ensure_app    
     app.bind(on_stop=lambda instance:


 During handling of the above exception, another exception occurred:

 Traceback (most recent call last):
   File "c:/Users/Wendelin/Documents/Programming/calculation/Calculator/experiment.py", line 39, in <module>
     screen_manager.add_widget(CalculatorScreen1(name = "screen1"))
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\uix\relativelayout.py", line 265, in __init__
     super(RelativeLayout, self).__init__(**kw)
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\uix\floatlayout.py", line 65, in __init__
     super(FloatLayout, self).__init__(**kwargs)
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\uix\layout.py", line 76, in __init__        
     super(Layout, self).__init__(**kwargs)
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\uix\widget.py", line 361, in __init__       
     rule_children=rule_children)
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\uix\widget.py", line 469, in apply_class_lang_rules
     rule_children=rule_children)
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\builder.py", line 538, in apply        
     rule_children=rule_children)
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\builder.py", line 659, in _apply_rule
     child, crule, rootrule, rule_children=rule_children)
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\builder.py", line 657, in _apply_rule  
     root=rctx['ids']['root'], rule_children=rule_children)
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\uix\widget.py", line 469, in apply_class_lang_rules
     rule_children=rule_children)
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\builder.py", line 538, in apply        
     rule_children=rule_children)
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\builder.py", line 707, in _apply_rule  
     e), cause=tb)
 kivy.lang.builder.BuilderException: Parser: File "c:\Users\Wendelin\Documents\Programming\calculation\Calculator\calculatorgui.kv", 
line 38:
 ...
      36:        size_hint_x: None
      37:        width: "30dp"
 >>   38:        text: app.angle_mode_text
      39:
      40:
 ...
 BuilderException: Parser: File "c:\Users\Wendelin\Documents\Programming\calculation\Calculator\calculatorgui.kv", line 38:
 ...
      36:        size_hint_x: None
      37:        width: "30dp"
 >>   38:        text: app.angle_mode_text
      39:
      40:
 ...
 AttributeError: 'NoneType' object has no attribute 'bind'
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\builder.py", line 249, in create_handler
     return eval(value, idmap), bound_list
   File "c:\Users\Wendelin\Documents\Programming\calculation\Calculator\calculatorgui.kv", line 38, in <module>
     text: app.angle_mode_text
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\parser.py", line 75, in __getattribute__
     object.__getattribute__(self, '_ensure_app')()
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\parser.py", line 70, in _ensure_app    
     app.bind(on_stop=lambda instance:

   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\builder.py", line 692, in _apply_rule  
     rctx['ids'])
   File "c:\Users\Wendelin\Documents\Programming\calculation\venv\lib\site-packages\kivy\lang\builder.py", line 254, in create_handler
     cause=tb)

所以看起來我以某種方式無法正確訪問應用程序實例。 但是，我查看了 Kivy 文檔，並按照規定使用了應用程序標識符。

我應該做些什么？ 任何幫助將不勝感激。

Answer 1

問題是在加載kv文件時未定義App中的Properties 。 您可以通過將Builder.load_file()移動到App來糾正該問題，以便已定義Properties ：

screen_manager = ScreenManager()


class Calculator(App):
    expression_tokens = ListProperty([])
    expression_value = StringProperty("")
    angle_mode = StringProperty("degrees")
    angle_mode_text = StringProperty("D")
    button_mode = NumericProperty(1)
    button_mode_text = StringProperty("1ST")
    store_mode = BooleanProperty(False)


    def build(self):
        Builder.load_file("calculatorgui.kv")
        screen_manager.add_widget(CalculatorScreen1(name = "screen1"))
        screen_manager.add_widget(CalculatorScreen2(name = "screen2"))
        return screen_manager