Kivy: ScreenManager - 访问子属性

Question

我正在构建一个应用程序，我需要它重复倒计时到零，直到达到时间限制。这一切都很好，但我目前的问题是，当它结束时，我希望其中一个标签显示“已完成”并尝试使用 ids 方法，但我总是收到一条 KeyError: 'count_down1' 消息，因为应用程序崩溃了就在调用 finish_callback() 函数的最后。

我是 kivy 的新手，但我最好的猜测是 self.ids[] 指的是在根小部件（即 WindowManager）中定义的 id，但 id: 'count_down1' 在一个WindowManager 的子窗口部件（即 SecondWindow）。然而，即使这是正确的，我也无法弄清楚如何纠正这个问题，也没有成功地从其他类似问题中提取正确答案。

py文件

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.animation import Animation
from kivy.properties import NumericProperty
from random import randint


class MainWindow(Screen):
    pass

class SecondWindow(Screen):
    pass


class WindowManager(ScreenManager):
    a = NumericProperty(0)
    b = NumericProperty(0)
    run_t = 5
    min = 3
    max = 7

    def reset(self):
        self.a = 0
        self.b = 0

    def start(self, *args):
        self.a = randint(self.min, self.max)
        self.anim = Animation(a = 0, duration = self.a)
        if self.run_t - self.b <= self.max:
            self.a = self.run_t - self.b
            print("a=", self.a, "b=", self.b)
            self.anim = Animation(a = 0, duration = self.a)
        else:
            print(self.run_t - self.b)
            self.anim.bind(on_complete = self.start)
    
        self.anim.start(self)

    def count_up(self):
        self.anim = Animation(b = self.run_t, duration = self.run_t)
        self.anim.bind(on_complete = self.finish_callback)
        self.anim.start(self)

    def finish_callback(self, animation, param):
        print('in finish_callback')
        end_1 = self.ids['count_down1']
        end_1.text = 'Finished'
        #^^this is where the error occurs^^


 kv = Builder.load_file("updown.kv")

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

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

kv 文件

WindowManager:
    MainWindow:
    SecondWindow:

<MainWindow>:
    name: "home"

    FloatLayout:        
        Button:
            pos_hint: {"x":0.4, "y":0.05}
            text: "Go!"
            on_release:
                root.manager.reset()
                root.manager.start()
                root.manager.count_up()
                root.manager.current = 'low'

<SecondWindow>:
    name: 'low'

    FloatLayout:        
        Label:            
            id: count_down1
            text: str(round(root.manager.a, 1))
            pos_hint: {"x": 0.4, "y": 0.55}
        Label:           
            id: count_up1
            text: str(round(root.manager.b, 1))
            pos_hint: {"x": 0.4, "y": 0.3}
        Button:
            background_color: 0.5,0.1,1,1
            text: 'Cancel'
            pos_hint: {"x":0.4, "y":0.05}
            on_release:
                root.manager.current = "medium"

<TextInput>
    size_hint: 0.24,0.1
    font_size: 35

<Button>
    font_size: 20
    color:1,0.2,0.5,1
    size_hint: 0.2, 0.1
    background_color: 0.5,0.8,0.2,1

<Label>
    font_size: 20
    color:1,0.2,0.5,1
    size_hint: 0.2, 0.1
    background_color: 0.5,0.2,0.9,1

出于可读性目的，我已尝试删除所有不必要的代码。总之，我认为我的问题是如何访问和更改子窗口小部件的属性？任何帮助将不胜感激！

Answer 1

问题 - KeyError

receive a KeyError: 'count_down1' message as the app crashes right at the end upon calling the finish_callback() function.

根本原因

id: count_down1 未在 ScreenManager 中定义。它在 SecondWindow() 中定义，但 ScreenManager 无权访问它。

Kv language » Referencing Widgets

id 的范围限于其声明的规则，因此在您的应用中 count_down1 无法在 <SecondWindow> 规则之外访问。

解决方案

将id: second_window添加到实例化对象，SecondWindow:以便您可以引用在SecondWindow
将self.ids[count_down1]替换为self.ids.second_window.ids.count_down1

片段 - kv 文件

WindowManager:
    MainWindow:
    SecondWindow:
        id: second_window

片段 - py 文件

def finish_callback(self, animation, param):
    print('in finish_callback')
    self.ids.second_window.ids.count_down1.text = 'Finished'

Kivy: ScreenManager - 访问子属性

Kivy: ScreenManager - Accessing child properties

python

kivy

kivy-language