Kivy多窗口切换应用出现AttributeError: release问题求助

开发一个包含三个按钮的Kivy应用，实现窗口切换功能，涵盖调查、超链接、清单三类界面。运行时出现AttributeError: release错误，无法定位问题，以下是代码及报错信息。

Python代码（Test Integration.py） #

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen

class FirstWindow(Screen):
    pass

class SecondWindow(Screen):
    pass

class ThirdWindow(Screen):
    pass

class WindowManager(ScreenManager):
    pass

kv = Builder.load_file("Test Integration.kv")

class MyMainApp(App):
    def build(self):
        return kv

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

KV文件（Test Integration.kv） #

WindowManager:
    FirstWindow:
    SecondWindow:
    ThirdWindow:

<FirstWindow>:
    name: "Main Menu"

    BoxLayout:
        orientation: "vertical"
        size: root.width, root.height
    
        Label:
            text: "Safety Checklist"
            font_size: 24
            on_release: app.root.current = "Checklist"
            root.manager.transition = "left"


    name: "Test Button."

    Button:
        text: "Please complete our survey!"
        on_release:
            import webbrowser
            webbrowser.open('https://forms.gle/k6cfYEU1snzpykxY9')


    name: "Checklist"

    BoxLayout:
        orientation: "vertical"
        size: root.width, root.height
    
        Label:
            text: "Checklist: Do you acquired all the necessary safety equipment?"
            font_size: 24
    
        GridLayout:
            cols:2
    
            Label:
                text: "Do you have your safety gloves with you?"
                font_size:16
            CheckBox:
                on_active: root.checkbox_click(self, self.active, "Do you have your safety gloves with you?")
            Label:
                text: "Do you have your safety boots with you?"
                font_size:16
            CheckBox:
                on_active: root.checkbox_click(self, self.active, "Do you have your safety boots with you?")
            Label:
                text: "Do you have your safety goggles with you?"
                font_size:16
            CheckBox:
                on_active: root.checkbox_click(self, self.active, "Do you have your safety goggles with you?")
            Label:
                text: "Do you have your helmet with you?"
                font_size:16
            CheckBox:
                on_active: root.checkbox_click(self, self.active, "Do you have your helmet with you?")
    
        Label:
            id: output_label
            text: "You are recommended to acquire or purchase the missing safety equipment."
    
    Button:
        text: "Return to main menu."
        on_release:
            app.root.current = "Main Menu"
            root.manager.transition = "right"

报错信息 #

Traceback (most recent call last):
File "C:\Users\nicho\PycharmProjects\Temasek Polytechnic MP (Software App)\venv\lib\site-packages\kivy\lang\builder.py", line 729, in _apply_rule
raise AttributeError(key)
AttributeError: release

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "C:\Users\nicho\PycharmProjects\Temasek Polytechnic MP (Software App)\Test Integration.py", line 17, in <module>
kv = Builder.load_file("Test Integration.kv")
File "C:\Users\nicho\PycharmProjects\Temasek Polytechnic MP (Software App)\venv\lib\site-packages\kivy\lang\builder.py", line 305, in load_file
return self.load_string(data, **kwargs)
File "C:\Users\nicho\PycharmProjects\Temasek Polytechnic MP (Software App)\venv\lib\site-packages\kivy\lang\builder.py", line 407, in load_string
self._apply_rule(
File "C:\Users\nicho\PycharmProjects\Temasek Polytechnic MP (Software App)\venv\lib\site-packages\kivy\lang\builder.py", line 660, in _apply_rule
child.apply_class_lang_rules(
File "C:\Users\nicho\PycharmProjects\Temasek Polytechnic MP (Software App)\venv\lib\site-packages\kivy\uix\widget.py", line 470, in apply_class_lang_rules
Builder.apply(
File "C:\Users\nicho\PycharmProjects\Temasek Polytechnic MP (Software App)\venv\lib\site-packages\kivy\lang\builder.py", line 540, in apply
self._apply_rule(
File "C:\Users\nicho\PycharmProjects\Temasek Polytechnic MP (Software App)\venv\lib\site-packages\kivy\lang\builder.py", line 736, in _apply_rule
raise BuilderException(
kivy.lang.builder.BuilderException: Parser: File "C:\Users\nicho\PycharmProjects\Temasek Polytechnic MP (Software App)\Test Integration.kv", line 17:
...
15:            font_size: 24
16:            on_release:

>> 17:                app.root.current = "Checklist"
>> 18:                root.manager.transition = "left"
>> 19:
>> ...
>> AttributeError: release
>> File "C:\Users\nicho\PycharmProjects\Temasek Polytechnic MP (Software App)\venv\lib\site-packages\kivy\lang\builder.py", line 729, in _apply_rule
>> raise AttributeError(key)

Process finished with exit code 1

问题修复方案 #

1. 解决AttributeError: release核心问题 #

KV文件中给Label控件绑定了on_release事件，但Label不支持该事件，只有Button、ToggleButton等可交互控件才有on_release。将触发界面切换的Label替换为Button：

# 原代码
Label:
    text: "Safety Checklist"
    font_size: 24
    on_release: app.root.current = "Checklist"
    root.manager.transition = "left"

# 修改后
Button:
    text: "进入安全清单"
    font_size: 24
    on_release:
        app.root.current = "Checklist"
        root.manager.transition.direction = "left"

2. 修正KV文件结构错误 #

原KV文件把三个Screen的内容全部塞进<FirstWindow>，还重复定义name属性，导致ScreenManager无法识别独立窗口。需要分别定义每个Screen：

WindowManager:
    FirstWindow:
    SecondWindow:
    ThirdWindow:

<FirstWindow>:
    name: "Main Menu"
    BoxLayout:
        orientation: "vertical"
        size: root.width, root.height
        # 主菜单按钮
        Button:
            text: "进入安全清单"
            font_size: 24
            on_release:
                app.root.current = "Checklist"
                root.manager.transition.direction = "left"
        Button:
            text: "填写我们的调查！"
            font_size: 20
            on_release:
                import webbrowser
                webbrowser.open('https://forms.gle/k6cfYEU1snzpykxY9')

<SecondWindow>:
    name: "Test Button"
    # 此处可添加第二个窗口的UI内容

<ThirdWindow>:
    name: "Checklist"
    BoxLayout:
        orientation: "vertical"
        size: root.width, root.height
        # 清单内容...

3. 修复屏幕过渡设置错误 #

原代码root.manager.transition = "left"写法错误，需设置过渡方向属性：

root.manager.transition.direction = "left"

4. 添加缺失的复选框处理方法 #

KV文件中调用了root.checkbox_click，但ThirdWindow类未定义该方法，需在Python代码中补充：

class ThirdWindow(Screen):
    def checkbox_click(self, checkbox, value, item):
        if value:
            self.ids.output_label.text = f"已确认拥有：{item}"
        else:
            self.ids.output_label.text = f"未确认拥有：{item}"

内容的提问来源于stack exchange，提问作者Nicholas