Kivy 'NoneType' 对象没有属性 'ids'

问题描述

我在我的 Kivy 应用程序中收到以下错误，但我不知道为什么以及如何解决它:

I am receiving the following error in my Kivy application but I am not sure why and how to fix it:

File "main.py", line 16, in __init__
self.seq_text_box = self.parent.ids.seq_text_box
AttributeError: 'NoneType' object has no attribute 'ids'

基本上，我要做的只是访问 MenuBar 类的方法中的文本框.我是新手，所以很可能我误解了一些东西.

Basically, all I'm trying to do is access the text box within the methods of the MenuBar class. I'm new to this so it's likely I'm misunderstanding something.

.py 文件

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.textinput import TextInput


class SequenceTextBox(TextInput):

    pass
    #...


class MenuBar(BoxLayout):

    def __init__(self, **kwargs):
        super(MenuBar, self).__init__(**kwargs)
        self.seq_text_box = self.parent.ids.seq_text_box

    def go(self):

        print(self.seq_text_box.text)


class MinuRoot(BoxLayout):
    pass


class MinuApp(App):
    pass


if __name__ == '__main__':
    MinuApp().run()

.kv 文件

MinuRoot:

<MinuRoot>:
    orientation: "vertical"
    MenuBar
    SequenceTextBox
        id: seq_text_box

<MenuBar>:
    height: "40dp"
    size_hint_y: None
    Button:
        text: "Go!"
        on_press: root.go()

<SequenceTextBox>:
    focus: True

感谢您的帮助:)

推荐答案

您可以将 seq_text_box 存储为 MenuBar 的 .html#kivy.properties.ObjectProperty" rel="nofollow">ObjectProperty 并在 kv 文件中设置:

You can store seq_text_box as an ObjectProperty of MenuBar and set it in the kv file:

class MenuBar(BoxLayout):
    seq_text_box = ObjectProperty()
    def go(self):
        print(self.seq_text_box.text)

在kv文件中:

<MinuRoot>:
    orientation: "vertical"
    MenuBar:
        seq_text_box: seq_text_box
    SequenceTextBox:
        id: seq_text_box

您收到错误的原因是因为在构造函数中，ids 尚未根据 kv 文件中指定的规则填充.

The reason you receive the error is because in the constructor the ids haven't been populated from the rules specified in the kv file.

如果您确实想使用普通属性，可以安排 Clock 事件:

If you do want to use a plain attribute, you can schedule a Clock event:

class MenuBar(BoxLayout):
    def __init__(self, **kwargs):
        super(MenuBar, self).__init__(**kwargs)
        Clock.schedule_once(self.init_seq_text_box, 0)

    def init_seq_text_box(self, *args):
        self.seq_text_box = self.parent.ids.seq_text_box

这将为下一帧安排对 init_eq_text_box 的调用，届时将填充 ids.

This will schedule a call to init_eq_text_box for the next frame, when ids will be populated.

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