将变量从 .py 文件传递到 .kv 文件

Question

我是 Kivy 的新手，正在工作中学习。我对如何使用各种小部件和嵌套布局有基本的了解。代码如下（另存为GUI.py）：-

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

class TestScreen(Screen):
    pass

class VariableScreen(Screen):
    pass

class SummaryScreen(Screen):
    pass

class ProgressScreen(Screen):
    pass

class CompletedResultsScreen(Screen):
    pass

class SavedResultsScreen(Screen):
    pass

class ScreenManagement(ScreenManager):
    pass

GUI_code = Builder.load_file("GUI.kv")

class GUIWindow(App):        #App class is inherited
    sampletext = StringProperty("Five times Five")

    def build(self):
        return GUI_code

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

GUI.kv 文件包含以下内容：

#: import FadeTransition kivy.uix.screenmanager.FadeTransition

ScreenManagement:
    transition: FadeTransition()
    TestScreen:
    VariableScreen:
    SummaryScreen:
    ProgressScreen:
    CompletedResultsScreen:
    SavedResultsScreen:

<TestScreen>:
    name: "Test_Screen"
    FloatLayout:
        Label:
            text: "Test"
            size_hint: 0.1,0.1
            pos_hint: {"right":0.5,"top":1}
        Label:
            text: app.sampletext
            size_hint: 0.1,0.1
            pos_hint: {"right":0.1,"top":1}
        Button:
            on_release: app.root.current = "Saved_Results_Screen"
            text: "Saved Results"
            size_hint: 0.1,0.1
            pos_hint: {"left":1,"bottom":1}
            font_size: 15
        Button:
            on_release: app.root.current = "Variable_Screen"
            text: "Variable"
            size_hint: 0.1,0.1
            pos_hint: {"right":1,"bottom":1}
            font_size: 15

只发布了 .kv 文件的相关部分。一些字符串必须从 .py 文件传递到 .kv 文件。该问题已在下面 link:

中得到解决

Pass variable value from main.py to .kv file

根据那里的建议，我使用 StringProperty class 在 GUIWindow class 中放置了示例文本。（还尝试了一个简单的字符串 sampletext = "Five times Five"。给出了同样的错误）

当第二个标签下的文本属性设置为文本时，代码不会运行：app.sampletext（应用window白色space 打开。它没有响应。需要重新加载 python 内核才能关闭它）

显示如下错误信息

 18: pos_hint: {"right":0.5,"top":1}
 19: Label:
 >>   20: text: app.sampletext
 21: size_hint: 0.1,0.1
 22: pos_hint: {"right":0.1,"top":1}
 ...
 AttributeError: 'NoneType' object has no attribute 'bind'

当文本属性设置为文本时运行正确："Five times Five"

谁能解释一下出了什么问题？

Answer 1

我找不到任何描述原因的文档，但当您解析文件时，解析器似乎正在尝试访问 app.sampletext，这是您在 App [=18] 之前所做的=] 连定义都没有，更不用说创建了。

将 Builder.parse 行移动到您的 build(self): 函数中，它将正常工作。

将变量从 .py 文件传递​​到 .kv 文件

Pass variable from .py file to .kv file

python

kivy

将变量从 .py 文件传递到 .kv 文件