ReferenceError：弱引用对象不再存在 Kivy DropDown

Question

运行这个 DropDown 示例可以正常工作。但是，经过一些使用/时间后，我收到错误 ReferenceError:weakly-referenced object no longer exist

这可能与 on_release:dropdown.open(self) 中的问题有关

关于为什么 on_parent: self.dismiss() 也不适用于我设置这些小部件的方式的奖励点。如果没有这个，我会在应用程序首次运行时出现子菜单项，并且启用此功能后，子菜单项会闪烁（出现并迅速消失）。

#!/usr/bin/kivy
import kivy
from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import Screen
from kivy.properties import ObjectProperty
from kivy.uix.dropdown import DropDown
from kivy.core.window import Window

Window.size = (400, 240)

sm = """

ScreenManager:
    id:manager
    canvas.before:
        Color:
            rgba: 0.5, 0.5, 0.5, 0.5
        Rectangle:
            pos: 0,0
            size: 800, 480
    Notes:
        id:Notes
        name: 'Notes'
        manager: manager

<Notes>:
    name: "Notes"
    orientation: "vertical"

    FloatLayout:
        size_hint: None, None

        canvas.before:
            Color:
                rgba: 1, 1, 0, 1    

        Button:

            id: mainbutton
            text: "Menu name"
            font_size: 20
            size_hint: None, None
            size: 150, 50
            pos: 20,400
            on_release:dropdown.open(self)

        CustomDropDown:
            id: dropdown
            #on_parent: self.dismiss()
            on_select: mainbutton.text = '{}'.format(args[1])

            Button:
                id: button1
                text: 'First Item'
                size_hint_y: None
                height: 40
                font_size: 18
                on_release: dropdown.select('First Item')

            Button:
                id: button2
                text: 'Second Item'
                size_hint_y: None
                height: 40
                font_size: 18
                on_release: dropdown.select('Second Item')

            Button:
                id: button3
                text: 'Third Item'
                size_hint_y: None
                height: 40
                font_size: 18
                on_release: dropdown.select('Third Item')

"""


class Notes(Screen):
    pass

class CustomDropDown(DropDown):
    pass

#dropdown = CustomDropDown()


class TestApp(App):

    def build(self):

        return Builder.load_string(sm)

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

Answer 1

来自：$Yourkivydir/kivy-examples/demo/showcase/data/screens

ShowcaseScreen:
    fullscreen: True
    name: 'DropDown'

    # trick to not lost the Dropdown instance
    # Dropdown itself is not really made to be used in kv.
    __safe_id: [dropdown.__self__]

    Button:
        id: btn
        text: '-'
        on_release: dropdown.open(self)
        size_hint_y: None
        height: '48dp'

    Widget:
        on_parent: dropdown.dismiss()

    DropDown:

        id: dropdown
        on_select: btn.text = 'Selected value: {}'.format(args[1])

        Button:
            text: 'Value A'
            size_hint_y: None
            height: '48dp'
            on_release: dropdown.select('A')

        Button:
            text: 'Value B'
            size_hint_y: None
            height: '48dp'
            on_release: dropdown.select('B')

        Button:
            text: 'Value C'
            size_hint_y: None
            height: '48dp'
            on_release: dropdown.select('C')

Answer 2

在子小部件中，CustomDropDown

使用 on_parent：self.dismiss()

当您点击主按钮时，菜单名称有时会报错，ReferenceError:weakly-referenced object no longer exist。如果没有ReferenceError，下拉列表闪烁（出现并快速消失）。原因是 DropDown 被关闭了。

没有 on_parent：self.dismiss()

它将在应用启动时显示 CustomDropDown 列表。单击主按钮菜单名称时，启动时出现的下拉列表消失了，但它显示的下拉列表的长度增加了两倍，即子菜单项重复了两次。

注意

下拉列表类似于弹出。它们是特殊的小部件。不要尝试将其作为孩子添加到任何其他小部件。如果这样做，它们将像普通小部件一样被处理，并且不会被隐藏在后台。

请参考以下示例，说明如何创建下拉列表。

示例

main.py

​​>

from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.dropdown import DropDown
from kivy.core.window import Window


Window.size = (800, 480)


class CustomDropDown(DropDown):
    pass


class Notes(Screen):
    pass


class MyScreenManager(ScreenManager):
    pass


class TestApp(App):
    title = "Kivy Drop-Down List Demo"

    def build(self):
        return MyScreenManager()


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

test.kv

#:kivy 1.10.0
#:import Factory kivy.factory.Factory

<CustomDropDown>:
    on_select: app.root.ids.Notes.ids.mainbutton.text = '{}'.format(args[1])

    Button:
        id: button1
        text: 'First Item'
        size_hint_y: None
        height: 40
        font_size: 18
        on_release: root.select(self.text)

    Button:
        id: button2
        text: 'Second Item'
        size_hint_y: None
        height: 40
        font_size: 18
        on_release: root.select(self.text)

    Button:
        id: button3
        text: 'Third Item'
        size_hint_y: None
        height: 40
        font_size: 18
        on_release: root.select(self.text)

<MyScreenManager>:
    canvas.before:
        Color:
            rgba: 0.5, 0.5, 0.5, 0.5
        Rectangle:
            pos: 0,0
            size: 800, 480
    Notes:
        id:Notes
        name: 'Notes'

<Notes>:
    orientation: "vertical"

    FloatLayout:
        size_hint: None, None

        canvas.before:
            Color:
                rgba: 1, 1, 0, 1

        Button:
            id: mainbutton
            text: "Menu name"
            font_size: 20
            size_hint: None, None
            size: 150, 50
            pos: 20,400
            on_release: Factory.CustomDropDown().open(self)

输出